COMPOSITE OPTICAL FILTER

RELATED CASES

This application claims the benefit of U.S. Provisional Application No. 61/589,153, filed January 20, 2012, and PCT/CA2012/000910 filed September 28, 2012, both incorporated herein by reference in their entirety.

TECHNICAL FIELD

[0001] The present disclosure relates generally to a composite optical filter. The composite optical filter may comprise two or more layers of a switching material.

BACKGROUND [0002] Optical filter have wide uses in controlling light. Optical filters may be used in glazings to control the flow of light and/or heat through the glazing, for examples in windows in buildings or vehicles (e.g. car, aircraft, watercraft or the like). Opthalmic devices (e.g. glasses, goggles, visors and other eyewear) may also employ optical filters to control or restrict the quantity and/or wavelength of light reaching the eye. The glazing may be a laminated glazing (e.g. 'safety' glass), or may be a single pane window, an insulated glazing unit (IGU) or part of an IGU, windshield, visor, wall, divider or the like.

[0003] Photochromies, electrochromics, thermochromics, hybrid photochromic/electrochromics liquid crystal, nanocrystal, and suspended particle displays have all been used in various optical filter applications, and selection of a particular technology may depend on the desired use. For example, 'privacy' glass that may be switched between transparent and opaque states may use a liquid crystal or suspended particle material, while eyeglasses that darken automatically in the sun and fade to a faintly colored, or uncoloured state when away from sunlight may employ a combination of photochromic and thermochromic technologies. US 20070019273 describes an automotive application (window) employing partially photochromic window glass - this material is described as darkening in sunlight, and clearing in dim light or darkness. Some other examples of photochromic glass include PHOTOGRAY EXTRA™ and PHOTOBROWN EXTRA™, available from Corning Glass Works.

-l- [0004] Some organic materials may be transitionable between different coloration states, and provide a range of colors. US 2011/0003070 describes viologen compounds that may be red, purple, blue, green or the like. While highly colored materials may be desirable for some applications, a neutral color, or a material that is dark without an overtly colored state may be useful for some applications.

SUMMARY

[0005] The present disclosure relates generally to a composite optica] filter. The composite optical filter may comprise two or more layers of a switching material. The layers of switching material may be transitionable between states of higher and lower light transmissibility.

[0006] In accordance with one aspect, there is provided a composite optical filter comprising a first layer of a first switching material; and a second layer of a second switching material; the first and second layers of switching material disposed between a first and a second substrate. In accordance with another aspect, the composite optical filter may further comprise a light source. The light source may be a layer within the composite optical filter, or may be alone one or more edges.

[0007] In accordance with another aspect, the composite optical filter may further comprise one or more than one transparent layers disposed between the first and second layers of switching material. In accordance with another aspect, the one or more transparent layers may comprise a light source. In accordance with another aspect, the transparent layer may comprise a first and a second plastic layer with an adhesive layer disposed therebetween. In accordance with another aspect, the transparent layer may comprise a conductive layer on each side, the first and second switching materials each in contact with a conductive layer. In accordance with another aspect, the conductive layer may be discontinuous, providing a first and a second electrode, each of the first and second electrodes in contact with the same side of the layer of switching material.

[0008] In accordance with another aspect, there is provided a method of making a composite optical filter, comprising the steps of: providing a first layer of switching material comprising a first chromophore having a first absorption profile; providing a second layer of switching material comprising a second chromophore having a second absorption profile complementary to the first absorption profile; and disposing the first and second layers between a first and a second substrate. In another aspect, the method may further comprise a step of disposing one or more transparent layers between the first and second layers of switching material. [0009] In accordance with another aspect, there is provided a method of determining a combination of first and second chromophores to provide a neutral-color composite optical filter, comprising the steps of: obtaining a first chromophore and determining an absorbance profile and an absorbance maxima; selecting a second chromophore and determining an absorbance profile and absorbance maxima; wherein the difference in the absorbance maxima is from about 60nm to about 130 nm.

[0010] In accordance with another aspect, the first and second layers of switching material may each be independently transitionable from a light to a dark state with exposure to a first wavelength of light, and transitionable from a dark state to a light state with exposure to a second wavelength of light. In another aspect, the first and second layers of switching material may each be independently transitionable from a light to a dark state with exposure to a first wavelength of light, and transitionable from a dark state to a light state with application of a voltage. In another aspect, the first wavelength of light may be between about 350 and about 450 nm. In another aspect, the second wavelength of light is between 450 and 650 nm. In another aspect, the voltage may be from about 1.5 V to about 3V. [0011] In accordance with another aspect, a first layer of switching material may be disposed between a second layer of switching material and an external light source. In another aspect, a second layer of switching material may be disposed between the first layer of switching material and an external light source.

[0012] In accordance with another aspect, the first switching material and the second material may comprise the same, or different chromophores. In another aspect, the first and second chromophores are independently selected from a group consisting of Formula IA/B and Formula IIA/B. In another aspect, the first switching material comprises a first chromophore according to Formula IA/B. In another aspect, the second switching material comprises a second chromophore according to Formula IIA/B. In another aspect, the first chromophore may have an absorption maxima of from about 635 nm to about 670 nm in a dark state. In another aspect, the second chromophore may have an absorption maxima of from about 500 to about 590 nm in a dark state. In another aspect, each of the first and second chromophores have an absorption maxima in the visible range, and are separated by about 60 nm to about 130 nm in a dark state.

[0013] In another aspect, the first chromophore may be selected from a group consisting of SOOl, SI 09 and SI 58. In another aspect, the second chromophore may be selected from a group consisting of S164, S163, S162, S161, S151, S144, S155, S152, S140 and S137. In another aspect, the first chromophore may be SI 09 or SI 58, and the second chromophore may be S161, S162, S163 or S164.

[0014] In another aspect, a ratio of the PSS of the first chromophore and the second chromophore may be from about 1:1 to about 1 :2, to about 1 :3 or to about 1 :4. In another aspect, the composite optical filter may have a haze of about 5% or less. In another aspect, the first layer, the second layer or the first and second layers taken together may have an a*, a b* or an a* and a b* value from about -10 to about +10, or from about 0 to about +10. In another aspect, the first and second layers may have a substantially similar thickness. In another aspect, the first and second layers may have a thickness of from about 1.2 to about 1.5 mil.

[0015] In accordance with another aspect, there is provided a composite optical filter comprising: a first optical filter, a second optical filter and a transparent layer therebetween; the first and second optical filters each comprising: a first and second substantially transparent substrate; a first and second electrode disposed on the surface of at least one of the substrates; a switching material disposed between the first and second substrates and in contact with the first and second electrodes, the switching material comprising one or more compound having electrochromic and photochromic properties.

[0016] In accordance with another aspect, there is provided a composite optical filter comprising: a first optical filter and a second optical filter, the first and second optical filters each comprising; a first and a second transparent conductive layer; and a switching material disposed between and in electrical contact with the first and second transparent conductive layers, the switching material comprising one or more compound having electrochromic and photochromic properties. [0017] In accordance with another aspect, there is provided a composite optical filter comprising a at least two optical filters, each optical filter comprising a first, and optionally a second, substantially transparent substrate, a first and second electrode disposed on the surface of at least one of the substrates; a switching material disposed upon the first substantially transparent substrate and in electrical contact with first and second electrodes; and an electrical connector for electrically connecting the first and second electrodes of each of the first and second optical filter to a source of electric voltage. Each of the first and second optical filters may each be independently transitionable from a light state to a dark state on exposure to UV light and from a dark state to a light state with application of an electric voltage.

[0018] Each optical filter may further comprise an electrical connector for electrically connecting the first and second electrodes of each of the first and second optical filters to a source of voltage. The first and second optical filters may each be independently transitionable from a light state to a dark state on exposure to UV light and from a dark state to a light state with application of voltage.

[0019] In accordance with another aspect, there is provided a composite optical filter comprising: a first transparent conductive layer, a second transparent conductive layer and a first switching material disposed between the first transparent conductive layer and a first side of the second transparent conductive layer; a third transparent conductive layer, and a second switching material disposed between the third transparent conductive layer and a second side of the second transparent conductive layer; and an electrical connector for electrically connecting the first transparent conductive layer, second transparent conductive layer and third transparent conductive layer to a source of electric voltage; the first and second switching materials each independently transitionable from a light state to a dark state on exposure to UV light and from a dark state to a light state with application of the electric voltage.

[0020] In some aspects, the first and second switching materials may be placed in contact with each other, or may be separated by a transparent conductive or non-conductive layer. The electrodes of each of the first and second optical filters may be co-planar electrodes. Where the first and second switching materials are placed in contact, the first and second switching materials may comprise one or more components that are immiscible, or substantially immiscible. The composite optical filter may comprise a third or subsequent optical filters. The colour of optical filters of the composite optical filter may be selected to achieve a desired colour balance; the desired color balance may be a neutral color.

[0021] This summary does not necessarily describe the entire scope of all aspects. Other aspects, features and advantages will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and other features will become more apparent from the following description in which reference is made to the appended drawings wherein: [0023] Figure 1 shows a composite optical filter according to one embodiment.

[0024] Figure 2 shows a composite optical filter according to another embodiment.

[0025] Figure 3 shows a composite optical filter according to another embodiment.

[0026] Figure 4 shows a composite optical filter according to another embodiment.

[0027] Figure 5 shows a composite optical filter according to another embodiment. [0028] Figure 6 shows a schematic diagram of a control circuit for a composite optical filter, according to another embodiment

[0029] Figure 7 shows a transmission spectra of a composite optical filter over the visible light range in faded, partially faded and fully faded configurations, according to some embodiments. Solid line - both first and second switching material in faded state; dashed line - first switching material in a dark state, second switching material in a faded state; dotted line - first switching material in a faded state, second switching material in a dark state; alternating dot/dash line - both first and second switching materials in a dark state.

DETAILED DESCRIPTION

[0030] The disclosure provides, in part, a composite optical filter comprising a first layer of a first switching material and a second layer of a second switching material, the first and second layers disposed between a first and a second substrate. In some embodiments, the first and second switching materials may be part of optical filter components of a composite optical filter, with a common control circuit for application of a voltage for controlling the transition of the first and/or second switching material between a dark and faded state. The common control circuit may comprise a first and a second voltage regulator, to provide a different voltage to each of the first and second layers. In some embodiments, the composite optical filter may comprise a light source.

[0031] By combining two or more layers of switching material, or two or more optical filters (each independently transitionable from a dark state to a faded state upon exposure to an electric voltage or visible light, and from a faded state to a dark state up on exposure to UV light), a composite optical filter transitionable between a fully faded state (e.g. from about 60 to about 90% LT _A ) to a dark state that is opaque or substantially opaque (e.g. LT _A of about 0 to about 25% LTA) is provided. The first and second optical filter may each be faded or darkened to provide a greater range of LTA and/or a greater range of light transmission characteristics. In some embodiments, the composite optical filter may comprise a third or subsequent optical filters. In some embodiments, the colour of optical filters of the composite optical filter may be selected to achieve a desired colour balance. In some embodiments, a composite optical filter with first and second switching materials at a lower concentration of chromophore may provide a dark state that is darker (less light transmittance) than would be achieved by either switching material alone, using less chromophore overall, while maintaining a high light transmittance in a faded state. Thus, pairing first and second switching materials in a composite optical filter may provide for an optical filter with a greater dynamic range (greater contrast ratio) than would be achieved by a single optical filter. Additionally, reducing the total amount of chromophore may provide a cost advantage for a manufacturer. [0032] Composite optical filters according to various embodiments of the invention may have low power requirements for switching between dark and faded states. The composite optical filter may be useful for a variety of applications such as opthalmic devices (e.g. visors, masks, goggles, lenses, eyeglasses (prescription or not) or the like), architectural windows, vehicle windows and glazings, and vehicle sunroofs of various types including pop-up, spoiler, inbuilt, folding sunroofs, panoramic roof systems or removable roof panels. The composite optical filters may demonstrate relatively rapid switching between dark and light states, which may be advantageous in applications where frequent or rapid changes in lighting conditions occur, for example automotive applications or opthalmic applications. The composite optical filters may be stable and exhibit minimal change in light transmittance in response to temperature, which may be advantageous in applications where frequent or rapid changes in temperature conditions occur, for example automotive, architectural or opthalmic applications. The composite optical filters may exhibit photostability and durability suitable for use in various applications, including those referenced herein, and may be cycled between light and dark states many times.

[0033] A user may control the light transmissibility of a composite optical filter by controlling the voltage applied to the composite optical filter, the light it is exposed to, or both. Voltage may be applied continuously, or intermittently to switch the composite optical filter, or an optical filter of the composite optical filter from a dark to a faded state, or to maintain the composite optical filter or an optical filter of the composite optical filter in a faded state.

[0034] In some embodiments, each of the layers of switching material may be disposed on, or between, and in contact with, one or more conductive layers. The conductive layer(s) may be disposed on a substrate. The substrate may be glass or plastic.

[0035] By combining two or more layers of switching material that are each independently transitionable between a dark and a faded state, a composite optical filter transitionable from a substantially transparent state to a darker, or dark (e.g. where all, or substantially all of the visible light transmission is blocked. The composite optical filter may be opaque, and appear dark grey or black, state is provided. Each of the first and second switching materials, may be independently faded or darkened to provide a range of light transmissibility. In some embodiments, the composite optical filter may comprise a third or subsequent layer of switching material. [0036] Composite optical filters according to various embodiments of the invention may have low power requirements for cycling between dark and faded states. Such low power requirements may make the filters useful for a variety of applications such as opthalmic devices (e.g. visors, masks, goggles, lenses, eyeglasses (prescription or not) or the like), architectural windows, vehicle windows and glazings, and vehicle sunroofs of various types including pop-up, spoiler, inbuilt, folding sunroofs, panoramic roof systems or removable roof panels. Applications such as in-dash information panels or the like may be particularly suitable, as the composite optical filter can be rendered substantially opaque when it is desirable to have the information panel dark (masking the display), and can be switched to a light transmissible state when it is desirable to view the information displayed in the information panel. In some embodiments, the composite optical filter may exhibit minimal change in light transmissibility in response to temperature, which may be advantageous in applications where frequent or rapid changes in temperature conditions occur, for example automotive applications or opthalmic applications. In some embodiments, the composite optical filter may exhibit photostability and durability suitable for the intended use, and may be cycled between light and dark states many times. [0037] Referring to Figure 1, a composite optical filter according to an embodiment is shown generally at 10. A layer of a first switching material 12, and a layer of a second switching material 14, may be disposed between a first 16 and a second 18 substrate. Figure 2 shows an optical filter according to another embodiment 20. First 12 and second 14 layers of switching material are disposed between first 16 and second 18 substrates. A transparent layer 22 may be disposed between the layers of the first and second switching materials.

[0038] Referring to Figure 3, a composite optical filter according to another embodiment is shown generally at 25. An optical filter OF1 comprising first switching material 12 disposed between substrates 26, 28 and conductive layers 30, 32, and an optical filter OF2 comprising second switching material 14 disposed between substrates 34, 36 and conductive layers 38, 40 are disposed on opposing sides of transparent layer 22. Conductive layers (electrodes) 30, 32, and 38, 40 may be connected to first and second voltage sources, or first and second voltage regulators, via electrical connectors.

[0039] Referring to Figure 4, a composite optical filter according to another embodiment is shown generally at 50. An optical filter OF3 comprising first switching material 12 disposed between substrate 18 and transparent layer 22; conductive layer 42 is disposed between substrate 18 and first switching material 12. On the other side of transparent layer 22, optical filter, OF4 is disposed, comprising second switching material 14 disposed between substrate 16 and transparent layer 22, and conductive layer 44 disposed between substrate 16 and second switching material 14. Layer 22 may be an electrically insulating layer, separating OF 3 and OF4. [0040] In some embodiments, conductive layers 42, 44 may each be a discontinuous layer, each discontinuous conductive layer 42, 44 comprising first and second electrodes. The first and second electrodes of each discontinuous layer may be connected to first and second voltage sources, or first and second voltage regulators, via electrical connectors. PCT Publication WO2012/079160 describes methods of making such electrodes ("coplanar electrodes"), for example, by etching of a conductive layer applied to a substrate.

[0041] Referring to Figure 5, a composite optical filter according to another embodiment is shown generally at 60. A transparent layer 62 comprising transparent substrate 68 with conductive layers 64, 66 disposed on opposing sides of the substrate 68 forms a middle section of the composite optical filter 60. Transparent substrate 68 may be an electrically insulating material, the electrically insulating material may be plastic or glass. A layer of first switching material 12 is disposed between conductive layer 64 and conductive layer 30 of substrate 26; a layer of second switching material 14 is disposed between conductive layer 66 and conductive layer 40 of substrate 36. As an example, the illustrated configuration may provide for an optical filter OF5 comprising first switching material 12, conductive layers 30 and 64, substrate 26 and substrate 68; and a second optical filter OF6 comprising second switching material 14, conductive layers 40 and 66, substrate 36 and intervening substrate 68. Substrate 68 is shared between OF5 and OF6.

[0042] In some embodiments, a transparent layer may comprise a light source (coplanar with the composite optical filter), an adhesive layer, be electrically insulating, may comprise one or more layers of plastic or glass and/or may be rigid or flexible. US6447134 describes a planar light emitting device that may comprise a transparent layer. In other embodiments, the transparent layer may comprise a highly transparent organic light-emitting diode (TrOLED) (Cho 2011, Optics Express 1992):! 1 13-1121). The transparent layer may comprise a layer that is at least partially reflective, and may direct light from the transparent layer towards the inboard or outboard layer of switching material. Other examples of transparent, light emitting layers are described in US 8110984, US 7915815.

[0043] In some embodiments, a light source may be along one or more edges or sides of the composite optical filter. A light source along the one or more sides or edges may provide UV, VIS, or UV and VIS light (e.g. from separate UV light emitting diodes (LEDs) and VIS LEDs) across the switching material, and through the layers of the optical filter and display. The transparent layer may be configured to aid transmission light from the light source along one or more sides or edges across and/or through the layers of switching material, to darken or fade the switching material. A control circuit may control the LEDs so that when UV light is on, VIS is off, and vice versa. The control circuit may further comprise a switch, and may be connected to a power source, such as a battery, or an electrical system of a building or vehicle to provide power to the LEDs.

[0044] A light source may provide light in the 380-780 nm range (e.g. full spectrum light), or any wavelength or range therebetween. In some embodiments, the light source may provide light in the 380 nm -420 nm range or may provide light in the 450 nm to 550 nm or 550 nm -690 nm range to fade a switching material.

[0045] In some embodiments, the relative position of the first and second layers, or other components of the composite optical filter, may be described with reference to the light source. A layer that is closer to a light source may be referred to as 'outboard' relative to another (for an embodiment where the composite optical filter is installed dividing an interior from an exterior space, such as a window in a building or vehicle, and Outboard' may refer to a layer that is 'outside' of another, relative to exterior light which may illuminate the composite optical filter.

[0046] Conductive layers and electrodes of optical filters are connected to a voltage source, directly or via a voltage regulator. In some embodiments, the light source may be connected to a voltage source; the voltage source of the light source may be the same, or coupled to, a voltage source for the conductive layers and electrodes of the optical filters. The electrical circuits for controlling the application of voltage to the optical filter may be coupled, or may be independent. Where the electrical circuits for the optical filters may be coupled, they may share a common ground - in such an embodiment, the transparent layer in the middle of the composite optical filter may be a transparent conductive layer. Where first and second switching materials have different voltage requirements to effect the electrochromic change, the electrical circuits may be independent, or share a common voltage source with separate voltage regulators and switches. In some embodiments, a power source for a light source is separate from the voltage source for the optical filters. [0047] Conductive layer [0048] A transparent conductive layer (electrode) may comprise, for example, metals, metal alloys, metal oxides, conjugated organic polymers, conductive carbon-rich materials and fine wire meshes. Exemplary conductive materials include layers of indium tin oxide (ITO), doped tin oxide, doped zinc oxide, doped cadmium oxide, fluorine tin oxide, antimony tin oxide, cubic strontium germanium oxide, polyaniline, graphene, fullerenes, carbon nanotubes, PEDOT (poly(3,4- ethylenedioxythiophene)), PEDOT:PSS (poly(3,4- ethylenedioxythiophene) poly(styrenesulfonate)), and polypyrrole, as well as thin, substantially transparent metallic layers such as gold, silver, aluminum, and nickel alloy. Methods of applying the electrically conductive material to a substrate to form suitable conductive layers and electrodes are known, for example chemical deposition, sputter coating or the like. The conductive layer may be of thickness that provides adequate conductance for operation of the electrodes, and which does not appreciably interfere with the transmission of light. The thickness of the conductive layer may be from about 1 nanometer to about 90 microns, or any amount or range therebetween. In some embodiments, a conductive material may be dissolved in a suitable solvent and cast in a layer (a transparent conductive layer), and used in a composite optical filter without being applied to a substrate. Such a layer may be of any suitable thickness, from about 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 mm or any amount or range therebetween.

[0049] In some embodiments, the conductive transparent layer(s) may have a sheet resistance of from about 100 Ohms/square to about 10,000,000 Ohms/square; or any amount or range therebetween. In some embodiments, first and second switching materials may be in contact

[0050] Substrate

[0051] A substrate may be rigid or flexible - an optical filter comprising one or more flexible substrate(s) may be in the form of a film that may be applied to a rigid material, such as a pane of a window, or a lens. A substrate may comprise glass, plastics or thermoplastic polymers. Examples of glass include float glass, tempered glass, laminated glass, tinted glass, mirrored glass, reinforced glass, monolithic glass, multilayered glass, safety glass, bullet- resistant glass or "one-way" bullet-resistance glass. Examples of thermoplastic polymers include polyesters (PE), polycarbonates, polyamides, polyurethanes, polyacrylonitriles, polyacrylacids, (e.g. poly(methacrylic acid), including polyethylene terephthalate (PET), polyolefms (PO) or copolymers or heteropolymers of any one or more of the above, or copolymers or blends of any one or more of the above with poly(siloxane)s, poly(phosphazenes)s, or latex. Examples of polyesters include homopolymers or copolymers of aliphatic, semi-aromatic or aromatic monomeric units, for example polycondensed 4- hydroxybenzoic acid and 6-hydroxynapthalene-2-carboxylic acid (VECTRAN™) , polyethylene napthalate (PEN), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyhydroxyalkanoate (PHA), polyethylene adipate (PEA), polycaprolactone (PCL) polylactic acid (PLA), polyglycolic acid (PGA) or the like. Examples of polycarbonates include bisphenol A, polycarbonate or the like. Examples of thermoplastic polymers include polyethene (PE), polypropylene (PP) and the like. The substrate may have UV, IR or VIS light blocking characteristics. Other examples of substrate materials include ceramic spinel or aluminum oxynitride.

[0052] The substrate may be of uniform or varying thickness, and of any suitable dimension. For example, the substrate may have a thickness from about 0.01 mm to about 10 mm, or any amount or range therebetween, for example 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 mm, or from about 0.012 mm to about 10 mm, or from about 0.5 mm to 10 mm, or from about 1 mm to 5 mm, or from about 0.024 mm to about 0.6 mm, or from about 0.051 mm (2 mil) to about 0.178 mm (7 mil). In some embodiments, the thickness and/or material of a first substrate differs from the thickness and/or material of a second substrate. In some embodiments, a substrate with a conductive layer may be ITO-coated glass, or ITO-coated PET.

[0053] Switching material

[0054] A switching material is transitionable from a light state to a dark state on exposure to light of a first wavelength, or range of wavelengths, and from a dark state to a light state with application of a voltage, or on exposure to visible light of a second wavelength or range of wavelengths. A first range of wavelengths (including light of a first wavelength) includes light of from about 350 nm to about 420 nm, or any amount or range therebetween. A second range of wavelengths (including light of a second wavelength) includes light of about 450 nm to about 690 nm, or any amount or range therebetween. A switching material may further comprise one or more compounds having both photochromic and electrochromic properties (a hybrid P/E compound, or chromophore). Such a switching material may be alternately described as an auto-darkening material. The switching material may be optically clear. In some embodiments, the switching material may be a liquid, a solid, a semi-solid, a sol-gel or a gel. The liquid, sol-gel or gel may be of a range of viscosity. The thickness of the layer of switching material may affect the LT _A of the composite optical filter. For example, when comparing a thinner and a thicker layer of the same switching material, the thicker layer may provide a darker state (lower light transmission) Thickness may be uniform or non-uniform. Within a composite optical filter, first, second and/or subsequent layers of switching material may be of the same or different thicknesses. Thickness of a switching material may be from about 0.5 mil to about 10 mil, or any amount or range therebetween, for example, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10 mil, or any amount or range therebetween.

[0055] In some embodiments, the chromophore of a switching material is an organic species having ring-open and ring-closed isoforms (A and B isoforms), and is reversibly interconvertible between isoforms with application of light and/or voltage, respectively.

[0056] In some embodiments, the switching material may comprise one or more additional components. Additional components include one or more of a solvent, a supporting electrolyte, a polymer, a charge compensator, a charge carrier, a UV stabilizing agent, a UV blocking agent, a tinting agent, or the like. Some components may be able to fill more than one role in the switching material, for example, certain compounds may self-polymerize and fulfill the role of both dye and polymer (see for example, compounds of WO2004/015024 and PCT/CA2012/000910); some polymers may also have UV blocking capabilities; or the like. Some polymers may be a rheology modifier, a cross-linkable polymer, or both a rheology modifier and a cross-linkable polymer, or both. Conversely, in some embodiments, a given component may be made up of several individual compounds, e.g., the polymer component may be a copolymer comprising different monomeric units. [0057] Chromophores according to various embodiments may be selected from Formula IA/B and Formula II A/B. In some embodiments, Conversion between isomers may be light- induced, or may occur under some oxidative conditions such as electrochemical conditions as a result of application of a voltage, or a combination thereof. One or more chromophores may comprise from about 1% to about 25% (by weight) of the switching material, or any amount or range therebetween, for example, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20 or 24 wt%, or any amount or range therebetween.

(IIA) (IIB) wherein

X may independently be N, O or S;

Z may independently be N, O or S;

[0058] Each Ri may be independently selected from the group consisting of H, halo;

[0059] Each R ₂ may be independently selected from the group consisting of H, halo, a polymer backbone, alkyl or aryl; or, when both R ₂ together form -CH=CH- and form part of a polymer backbone;

[0060] Each R4 may be independently selected from the group consisting of

Each R.5 may be independently selected from the group consisting of H, halo, alkyl or alkoxy and;

[0061] Each of R6 _a , ^b, R6c, R7a, R-7b and R-7c may be independently selected from a group comprising one or more of H, halo, alkyl, alkoxy, carbonyl, siloxy, thioalkyl or aryl. The R.6a and R _7a position may alternately be referred to as the "5 position"; the and R ₇ b position may alternately be referred to as the "4 position"; the R^ and R _7c position may alternately be referred to as the "3 position" of the ring;

[0062] Each of R _9a , R _% , R _C , R9d and R _9e may be independently selected from the group consisting of H, halo, alkyl, alkoxy, thioalkyl, carbonyl, siloxy or aryl. [0063] In another aspect, R _6a and R6b, or R< _¾ and R _6c are each -CH=CH- and joined to form an unsaturated ring,

[0064] In another aspect, R _7a and R _7b, or R ₇ b and R _7c are each -CH=CH- and joined to form an unsaturated ring.

[0065] In another aspect, R _9a and or R _% and R _9C; or R _9c and R _9d , or R a and R _9e are each -CH=CH- and joined to form an unsaturated ring.

[0066] In another aspect, R _9c may be an alkyl, alkoxy or siloxy group, selected from a group comprising an alkyl group comprising from one to 20 carbons. In another aspect, one or more of Rio _a , Riob, Rio _o Rio _d ^m y t> ^e an alkoxy or siloxy group, comprising from one to ten oxygen atoms and from one to 20 carbons. In another aspect, an Ri _0b and an Rio _c are each O, and joined with a -CH ₂ - to form a 5 membered ring.

[0067] As used herein, "halogen" refers to F, CI, Br or I. The term "halo" is generic, and refers to any halogen moiety, for example fluoro- chloro-, bromo- or iodo-, or the like.

[0068] As used herein, "metal" as used herein refers to a transition metal, or an alkali metal such as Li, Na, K, or the like; or a metalloid such as B or Si, or the like.

[0069] As used herein, "alkyl" refers to any linear or branched, non-aromatic monocyclic or polycyclic, substituted or unsubstituted alkyl group of 1 to 50 carbons, for example 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, or 45, or any amount therebetween. Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, iso- butyl, sec-butyl, tert-butyl, 1-pentyl, iso-pentyl, neo-pentyl, hexyl, cyclopropane, cyclobutane, cyclopentane, cyclohexane or the like. The alkyl group may have one or more saturated or unsaturated bonds. The alkyl group may contain only carbon and hydrogen atoms, or may further incorporate one or more heteroatoms such as Si, N, O or S as part of the alkyl group (a heteroalkyl group). Examples of cyclic heteroalkyl groups include aziridine, oxirane, thiirane, oxaziridine, dioxirane, azetidine, oxetane, thietane, diazetidine, dioxetane, dithietane, azirine, oxirene, thiirene, azete, oxete, thiete, dioxete, dithiete, pyrrolidine, oxolane, thiolane, borolane, silolane, dithiolane, dioxolane, oxazolidine, piperidine, oxane, thiane, piperazine, morpholine or the like. An alkyl group with a Si heteroatom may be described as a 'silyl' or 'silane' group.

[0070] As used herein, "alkoxy" refers to any -O-R group, where R (and R' for an ether, below) may independently be H, alkyl, siloxy or aryl. Examples of alkoxy and siloxy groups include those with from 1 to 50 carbon or silicon atoms in a linear or branched chain, for example methoxy or ethoxy, or longer alkyl groups. Alkoxy groups include ethers (-R-O-R'- ), alcohol (-OH) or alkoxide (-R-O-metal) or the like. An alkyl group comprising an alkoxy substituent group may be referred to as an 'alkylalkoxy' group. An alkyl group comprising an Si heteroatom, and an alkoxy, or a siloxy group may be referred to as an alkylsiloxy, or silylsiloxy group.

[0071] As used herein, "carbonyl" includes aldehyde (R-COH), ketone (RCOR'), ester (RCOOR'), acyl (RR'C=0), carboxyl, thioester (COSR'), primary amide (CONH ₂ ), secondary amide (CONHR'), tertiary amide (CONR'R") or the like.

[0072] As used herein, "siloxane" refers to an (R) ₂ -Si-0-, where R may independently be H, alkyl, aryl, thioether or alkoxy. A siloxane may be branched or linear, substituted or unsubstituted, or comprise alternating Si and O atoms.

[0073] As used herein, "thioether" refers to an -S-R group where R may independently be H, alkyl, aryl, alkoxy or the like.

[0074] R', R", R'" may be alkyl chains that contain between 1 and 50 non-hydrogen atoms such as C, N, O, S, Si, B or P that may be branched or unbranched, that may be acyclic or cyclic, and that may contain any permutation of heteroatomic substituents such as N, O, S, Si, B or halogen. [0075] As used herein, "aryl" refers to a group or substituent derived from an aromatic ring compound where one or more hydrogen atoms are removed from the ring. An aryl group may alternately be referred to as an aromatic group. An aryl group may comprise a single atom species in the ring (e.g. all ring atoms may be carbon, such as in a phenyl ring - a 'carbocycle') or may comprise one or more heteroatoms in the ring - a "heteroaryl". An aryl group may be polycyclic. The carbocyclic, heterocyclic or polycyclic aryl group may comprise one or more substitutent groups (a substituted aryl) or be unsubstituted (an unsubstituted aryl). A carbocyclic aryl group may be substituted or unsubstituted phenyl or the like. A carbocyclic aryl group may be polycyclic.

[0076] A heterocyclic aryl group may be substituted or unsubstituted pyrrole, furan, thiophene, imidazole, pyrazole, oxazole, isoxazole, thiazole, isothiazole, triazole, furazan, oxadiazole, thiadiazole, dithiazole, tetrazole, pyridine, pyran, thiopyran, diazine, oxazine, thiazine, dioxine, dithiine, triazine, tetrazine, or the like. A polycyclic aryl group may be substituted or unsubstituted indole, isoindole, quinolone, isoquinoline, benzofuran, benzothiophene, acridine, dibenzothiophene, carbazole, dibenzofuran or the like.

[0077] As used herein, alkyl, heteroalkyl, alkoxy, alkylalkoxy or aryl groups may further comprise 1, 2, 3, 4, 5 or more substituent groups. Substituent groups may be independently selected from the groups comprising:

(i) hydrogen or halogen;

(ii) alkyl or alkoxy;

(iii) a derivative of group (ii) above in which one or more of the carbon atoms have been replaced with a heteroatom such as nitrogen, oxygen, sulfur, boron, silicon or phosphorous;

(iv) a derivative of groups (ii), (iii), or (ii) and (iii) above in which one or more of the hydrogen atoms have been replaced with a heteroatom such as nitrogen, oxygen, sulfur, fluorine, chlorine or bromine;

(v) a monocyclic or bicyclic cycloalkyl group containing from one to fifteen carbon atoms, or the like;

(vi) a derivative of group (v) above in which one or more of the carbon atoms have been replaced with a heteroatom such as nitrogen, oxygen, sulfur, boron, silicon or phosphorous; (vi) a derivative of groups (v), (vi), or (v) and (vi) above in which one or more of the hydrogen atoms have been replaced with a heteroatom such as nitrogen, oxygen, sulfur, fluorine, chlorine or bromine;

(vii) an aryl group;

(viii) a derivative of group (vii) above in which one or more of the hydrogen atoms have been replaced with a heteroatom such as nitrogen, oxygen, sulfur, fluorine, chlorine or bromine;

(ix) a carbonyl group;

(x) a nitrogen-based group such as cyano (-CN), primary amine (NH ₂ ), secondary amine (NHR'), tertiary amine (NR'R"), secondary amide (NHCOR'), tertiary amide

(NR'COR"), secondary carbamate (NHCOOR'), tertiary carbamate(NR'COOR"), urea or N- substituted urea (NR'CONR"R"'), secondary sulfonamide (NHS0 ₂ R'), tertiary sulfonamide (NR'S0 ₂ R"), wherein groups R', R", R" \ are defined supra;

(xi) an oxygen-based group e.g alcohol -OH, ether (OR'), primary carbamate (OCONH ₂ ) secondary carbamate (OCONHR'), tertiary carbamate (OCONR'R"), wherein groups R', R", etc., are defined supra.

(xii) a sulfur-based group such as -SH, thioether (SR'), sulfoxide (SOR ¹ ), sulfone (S0 ₂ R'), primary sulfonamide (S0 ₂ NH ₂ ), secondary sulfonamide (S0 ₂ NHR'), tertiary sulfonamide (S0 ₂ NR'R"), wherein groups R', R", R'" are defined supra.

[0078] In some aspects of the invention, R6 _a , R6b, R _6c , R-7a, R7b, R7c Rsa, Rsb, Rsc, R ₈ d, Rse, R _9a , R%, R9c, R d, R e, Rioa, Riob, iOc Riod may independently comprise an electron- withdrawing group (EWG), electron-donating group (EDG) or bulky group. It should be understood that the term "electron-accepting group" can be used synonymously herein with "electron acceptor" and "electron-withdrawing group". In particular, an "electron- withdrawing group" ("EWG") or an "electron-accepting group" or an "electron-acceptor" refers to a functional group that draws electrons to itself more than a hydrogen atom would if it occupied the same position in a molecule. Examples of EWG include halo, electron-poor heteroaryl groups, electron-poor substituted aryl groups, -N0 ₂ , - ⁺ NR ₃ , -^Ntb, -SO3H, -CN, CF ₃ , aldehyde, ester, carboxylic acid, carbonyl, carbonyl chloride, amide or the like. It should further be understood that the term "electron-donating group" can be used synonymously herein with "electron donor". In particular, an "electron-donating group" or an "electron- donor" refers to a functional group that donates electrons to a neighboring atom more than a hydrogen atom would if it occupied the same position in a molecule. Examples of EDG include -OH, OR, NH ₂ , NHR, NR ₂ , electron-rich heteroaryl groups, electron-rich substituted aryl groups, -O ^" , amine, alcohol, ether, carbamate, or the like.

[0079] A substituent group may comprise a siloxy or silyl component - for example silane, siloxy, alkylsiloxy, silanesiloxy, alkoxysilane, Formula XI, Formula XII, or the like - the substituent group may comprise:

wherein n and m are independently any integer from 0 to 20, or any range therebetween, or 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20.

[0080] A "bulky" group may be an alkyl, aryl, alkoxy, silane, siloxy, alkylsiloxy, silanesiloxy, alkoxysilane, or a substituted alkyl, aryl, alkoxy, silane, siloxy, alkylsiloxy, silanesiloxy, alkoxysilane, the bulky substituent group comprising at least two atoms selected from the group comprising C, N, O, Si or S. In some embodiments, a bulky substituent group is a substituted or unsubstituted ethyl, propyl, butyl, tert-butyl or pentyl group, or a substituted or unsubstituted alkoxy group. In some embodiments, a bulky substituent group is a substituted or unsubstituted formula XI or formula XII. In some embodiments, a bulky substituent group is an alkyl-substituted thiophene, or an alkyl-substituted phenyl, or an alkyl substituted benzothiophene or an alkyl substituted benzofuran.

[0081] Inclusion of a bulky substituent group may increase the, photostationary state, solubility, photostability or durability of a compound. As an illustrative example, and without wishing to be bound by theory, some positions of an internal or external thiophenyl ring may polymerize when subjected to oxidation conditions by application of a voltage. Inclusion of a bulky group at R _6a or R _7a (5-position), or or R _7b (4-position) of a thiophenyl ring may improve the durability of the compound when subjected to multiple cycles of electrooxidation. In some embodiments, a small (e.g. 1 or 2 carbon containing moieties such as methyl or ethyl) group in both 4 and 5 positions, or a larger bulky group (e.g. 3, 4, 5 or 6 carbon-containing moieties such as propyl, butyl (primary, secondary or tertiary), pentyl or hexyl in the 5 position may provide improved durability of the compound.

[0082] Compounds according to various embodiments of the invention may include one or more of the following:

[0083] Each Ri _; R ₂ may be independently selected from a group comprising H or F. [0084] Each R4 may each be independently selected from a group comprising one or more

( MS = tetramethyl silane)

[0085] Each R ₅ may be independently selected from a group comprising: H, methyl, ethyl, propyl, butyl, tert-butyl, thiophenyl, substituted thiophenyl, benzyl, substituted benzyl, -CH=CH-, -CH=CH-, -OCH3 _, C0 ₂ H.

[0086] Substituent groups of a substituted thiophene or substituted benzyl group may include -CN, methyl, ethyl, propyl, butyl, tert-butyl;

[0087] ¾ _a and R^, or !½, and R6 _C , or R _7a and R ₇ b, or R ₇ b and R _7c may each be a) - CH=CH- and fused to form a ring; or b) -CH ₂ -CH ₂ - and fused to form a ring; or c) -0-CH ₂ - and fused to form a ring;

[0088] One or more than one of:R6 _a , (5b, ₆ c; and/or R _7a , R ₇ b, R _7c ; and/or R9 _a , R% _> %, R9d, 9 _e ; and/or R] _0a , Riob, Rioc, Riod may each independently be selected from a group comprising one or more of: H, CI, Br, F, -CF3, -CN, -N0 ₂ , methyl, ethyl, propyl, iso-propyl, butyl, sec-butyl, iso-butyl, tert-butyl, saturated or unsaturated alkyl that is linear or branched with 5-12 carbons, -Si(Rn) ₃ , thiophene, substituted thiophene, benzyl, substituted benzyl, - CH2-CH2-, -CH=CH-, -CH=CH ₂ , -OCH ₃ , -COH, -OH, -C0 ₂ H, -COCH3, -C0 ₂ Y, - C(CH ₃ ) ₂ OH, -Si(CH ₃ ) ₃ , -CH ₂ CH ₂ OCH ₃ , -CH ₂ CH ₂ OH, -N(CH ₃ ) ₂ , -C0 ₂ CH ₃ , -OCH ₂ OCH ₃ , - S0 ₂ CH ₃ , -OCH ₂ C(CH ₃ ) ₃ , -OCH ₂ CH(CH ₃ ) ₂ , -OC(CH ₃ ) ₃ , -OCH=CH ₂ , -0(CH ₂ ) ₄ CN, - 0(CH ₂ ) ₄ OH, -0(CH ₂ ) ₃ OH, -C(CH ₃ ) ₂ OH, -OCH ₂ ) ₂ OCH ₃ ,

[0089] In some embodiments, each Ri i of -Si(Rn) ₃ may be independently selected from the group comprising R or -O-R, and wherein R is linear or branched, non-aromatic monocyclic or polycyclic, substituted or unsubstituted alkyl group of 1 to 20 carbons. In some embodiments, each R may be a heteroalkyl group comprising one or more of O, S, N or Si, or each R may be a saturated or unsaturated alkyl that is linear or branched with 1-12 carbons, or each R may be a substituted or unsubstituted methyl, ethyl, propyl, iso-propyl, butyl, sec -butyl, iso-butyl, tert-butyl, pentyl or hexyl. In some embodiments, for a compound according to Formula IA and IB, Ri and R ₂ are H or F, Z and X are each S,

Re _a , R6b, and Re _d may independently be -OCH ₃ , H, - C(CH ₃ ) ₃ or -Si(R _n ) ₃ ,

[0090] In some embodiments, for a compound according to Formula IIA and IIB, Ri and are H or F, Z is O, Ri _0a , Rio _b , Rioc and R _10d may independently be -OCH3, H, - C(CH ₃ ) ₃

[0091] In some embodiments, for a compound according to Formula IIA and IIB, where Ri and R ₂ are F and Z is O and all of R _10a , Riot> ₅ RiOc and iod are H, R _C is not an alkyl chain according to C ₄ H ₉ , C ₈ H ₁₇ or C ₁₂ H ₂₅ .

[0092] Examples of chromophores according to Formula IA/B and Formula IIA/B are shown below. Synthetic schema, photostationary state and sensitivity index for these and other chromophores according to Formula 1A/B and Formula IIA/B are described in commonly owned PCT Application PCT/CA2012/000910. The open-ring isoform (isoform A) is illustrated, and conditions to open and close the rings of the appropriate isoform are indicated herein (e.g. exposure to light, or application of voltage).

[0093] Solvent: A solvent component of a switching material may have one or more of the following characteristics: boiling point of about 150°C or greater, vapour pressure of about 0.001 mmHg or less at 20°C, Yellowness Index (YI) of about 6 or less; a flash point of about 80°C or greater, a melting point of about 40°C or less, is compatible with components of a switching material or coatable formulation, and does not interfere with darkening or fading of the switching material. The solvent component may be a mixture of one or more than one solvents. Examples of solvents include triglyme, tetraglyme, propylene carbonate, ethylene carbonate, ,2-butylene carbonate, delta- alerolactone, formamide, 3-methyl-2- oxazolidone, phthalide, tetramethylurea, dimethyl-2-methyl glutarate, diethyl succinate, triethylene glycol di-2 -ethyl butyrate, triethylene glycol bis(2-ethylhexanoate, butyrolactone, cyclopentanone, ethylene glycol phenyl ether; diethylene glycol monobutyl ether, 2(2- butoxyethoxy)ethyl acetate, diethyl adipate, dimethyl adipate, 2,2,4-trimethyl-l,3- pentanediol monoisobutyrate, propylene glycol diacetate, dibutyl itaconate, dimethylglutarate or the like. The one or more solvents may comprise from about 30% to about 90% (wt%) of the switching material, or any amount or range therebetween. In some embodiments, the solvent is optically clear, or substantially optically clear, and the one or more supporting electrolyte, rheology modifiers, gelling agents, polymers, co-solvents, accelerants, hardeners, epoxides and other components of a switching material or composition are soluble in the solvent

[0094] Supporting electrolyte: Supporting electrolytes may include alkali metal salts, tetralkylammonium salts or the like. Examples include tetrabutylammonium tetrafluoroborate, tetrabutylammonium hexafluorophosphate, tetrabutylammonium perchlorate, lithium bis(trifluoromethane sulfonimide), tetrabutylammonium bis((trifluoromethyl) suIfonyl)imide, triflate, lithium bis(oxatlato)borate, lithium perchlorate or the like. The one or more electrolytes may be present in an amount from about 0.1% to about 10% (by weight) or any amount or range therebetween, for example 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, or 9%, or any amount or range therebetween.

[0095] Polymer: The switching material may comprise one or more polymers. The one or more polymers may be a rheology modifier, a crosslinkable polymer, or both a rheology modifier and a crosslinkable polymer. A rheology modifier may increase the viscosity of the switching material to facilitate coating of the switching material on a substrate, , or into a mold or die. Examples of one or more polymers include polyvinyl alcohol (PVOH), polyvinyl acetate (PVA), polyvinylbutyral (PVB), poly(methyl methacrylate) (PMMA), nitrile rubber (NBR), polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), poly(dimethylsiloxane) (PDMS), poly(ethyl methacrylate) (PEMA), NBR, hydroxypropyl cellulose, PEG-DMA (poly(ethylene glycol) dimethacrylate), PHEMA (poly(2-hydroxyethyl methacrylate), Plexiglas™ G-UVT acrylic, polychloroprene, polybutadiene, PDMS-g-PEG (PEG-modified PDMS), PEO (polyethylene oxide), PEG-MEMA (PEG-methylether methacrylate), silicones, PDMS, PPGMA (poly(propylene glycol), EGDMA (ethylene glycol dimethacrylate), PVDC (polyvinylidene chloride), PVC (polychlorovinyl), PVDC-PVC, cyclo olefin copolymer (APEL™), carboxymethyl cellulose (CMC), SOLEF™ 21520, SOLEF™ 21508, zein, polyisobytulene-600, poly(ethylene-co-methacrylic acid (EMAA, SURLYN™ 60), polyethylene-co-(ethylacrylate), ethylacrylate, poly(vinylidene chloride-co- vinyl chloride), polyisoprene, polybutene, poly(sodium 4-styrene sulfonate), HEMA (hydroxyethyl)methacrylate or combinations thereof, or copolymers thereof. Cross-linkable polymers comprise one or more pendant -OH groups, and may be a homopolymer or copolymer. Examples of cross-linkable polymers include PVOH, PVA, PVB and PEO. One or more polymers may be present in an amount of about 0.5 wt% to about 20 wt%, or any amount or range therebetween, for example 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 wt%. Examples of PVB preparations that may be used in compositions or formulations according to various embodiments of the invention include one or more of B60H (Kuraray; MW of about 50-60K), B90 (Butvar, MW of about 70-100 K) and B72 (Butvar, MW of about 170-250 K). [0096] One or more sol-gels may also be included in a switching material; a sol-gel may be a rheology modifier. Examples of sol-gels include silicon-oxygen based sol-gels, aluminum- oxide based sol-gels or combinations thereof. The one or more polymers or sol-gels may be present in an amount from about 0.1% to about 10% (by weight)or any amount or range therebetween, for example 1 , 2, 3, 4, 5, 6, 7, 8, or 9%, or any amount or range therebetween. [0097] The switching material may comprise components (hardeners, accelerants, crosslinkers or the like) to facilitate cross-linking of the switching material before, during or after coating on a substrate layer or surface. .

[0098] Cross-linker: A cross-linker (cross-linking agent) may comprise two or more reactive groups; reactive groups may independently be, for example, aldehyde, epoxide, isocyanate, silane or the like. Examples of crosslinking agents include aldehyde, isocyanate, melamines, phenolic resins or the like. A hardener may be used with some crosslinking agents comprising an epoxide reactive group. Examples of aldehyde crosslinkers include terephthalaldehyde and the like, Examples of epoxides include DER736, DER732 (both from Dow Chemical), bisphenol A diglycidyl ether (BADGE), 1 ,4-butanediol diglycidyl ether, 1 ,4- cyclohexanedimethanol diglycidyl ether, 1,2,5,6-diepoxycyclooctane, resorcinol diglycidyl ether, tris(4-hydroxyphenyl)methane triglycidyl ether or diglycidyl 1 ,2- cyclohexanedicarboxylate and the like. Examples of isocyanate crosslinking agents include aromatic and aliphatic diisocyanates; examples of aliphatic diisocyanates include hexamethylene diisocyanate (e.g. DESMODUR™ N100, N3300A, N3600), isophorone diisocyanate, methylene dicyclohexyl diisocyanate, xylylene diisocyanate, cyclohexane diisocyanate, tetramethyl xylylene diisocyanate, isopropenyl dimethylbenzyl isocyanate, trimethylhexamethylene diisocyanate, norbornane diisocyanate or the like. Examples of aromatic diisocyanates include diphenylmethane diisocyante, toluene diisocyanate, p- phenylene diisocyanate, naphthalene diisocyanate or the like. The cross linker may be present in a switching material in an amount of about 0.01% to about 10%, or any amount or range therebetween, for example 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9 wt%, or any amount or range therebetween.

[0099] Hardeners: A hardener (curing agent") may be an anhydride, for example MHHPA (methylhexahydrophthalic anhydride) THPA (tetrahydropthalic anhydride), MTHPA (methyltetrahydropthalic anhydride), HHPA (hexhydropthalic anhydride), 4- methylhexahydrophthalic anhydride or the like. A hardener may be present in a switching material in an amount of about 0.5% to about 10%, or any amount or range therebetween, for example 1, 2, 3, 4, 5, 6, 7, 8, or 9 wt%.

[00100] Accelerant: examples of accelerant ("catalyst") used with materials comprising an epoxy reactive group may include A C-2, AMC-3, ATC-3 (AMP AC Fine Chemicals), Zinc 2-ethyl hexanoate (99%, or 80% in mineral spirits), AC8 (Available from Broadview), CXC1612 or CXC1613 (King Industries), l ,4-diazabicyclo[2.2.2]octane (DABCO), HC\, p- toluenesulfonic acid, potassium -butoxide, Tyzor ZEC (Dorf-Ketal), Tyzor AA75 (Dorf- Ketal), Titanium tetraisopropoxide, Copper (II) chloride. Where the crosslinker is an aldehyde, the accelerant may be an acid, such as a Lewis acid. Examples of accelerants that may be used with materials comprising an isocyanate reactive group may include dibutyltin dilaurate, dibutyltin diacetate, dibutyltin oxide, transition metal (e.g. Mn, Sn, V, Bi, Zn, Co,

Zr, Al, Cr, Ti, Cu) complexes of acetylacetonate, octanoate, chelate (e.g. metal chelates from King Industries) or the like The accelerant may be present in a switching materialin an amount of about 0.001% to about 1%, or any amount or range therebetween, for example, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9 wt%.

[00101] Co-solvent: a co-solvent may be used to dilute a switching material for coating on a substrate. A co-solvent is compatible with other components of the formulation - for example, other components are soluble in, and unreactive with, the co-solvent. The co- solvent may be, for example, toluene, tetrahydrofuran, methyl ethyl ketone, or ethyl acetate. A co-solvent may dilute a switching material from about 5% to about 50%, or any amount or range therebetween. After coating, the co-solvent may be removed (e.g. by evaporation) before applying a second substrate, or another layer of switching material, or before incorporating the optical filter comprising the switching material into a composite optical filter.

[00102] Preparation of optical filters

[00103] Composite optical filters according to various embodiments of the invention may be manufactured by any suitable process, for example, wet-coating the switching material onto one or more transparent conductive layers, allowing for a roll-to-roll manufacturing process, and avoiding sputter-coating or vapour deposition , or other more complex and/or more expensive processes. In some embodiments, the switching material may be formulated for application as a liquid, gel or sol-gel, and thickened, set or cross-linked after application, forming a layer on the transparent substrate, layer or conducting material.

[00104] Optical filters of the composite optical filters according to various embodiments of the invention may be prepared by any suitable processing method - WO2010/142019 describes several of these, including roll-to-roll processing. Generally, a first substrate or layer is provided - in some embodiments this substrate may comprise a conductive layer comprising one or more electrodes; in some embodiments the layer may be a transparent conductive layer. The switching material is coated or deposited on a first side of the substrate or layer. A second layer may be laminated on the switching material - the second layer may be a non-conductive layer, a transparent conductive layer, or a substrate comprising a transparent conductive material (e.g. ITO coated PET). In another embodiment, a switching material applied to a first substrate is placed in contact with a switching material applied to a second substrate, to provide a composite optical filter. [00105] In one embodiment, the switching material has a high viscosity at room temperature and is made into a lower-viscosity liquid by heating to allow it to be applied or coated onto the substrates. In one embodiment, the switching material is heated (to facilitate flow) and pressed between the substrates. According to another embodiment of the invention, the switching material is first cast as a liquid and then further treated to increase the viscosity of the material to form a gel. For example, the switching material can be dried wherein the solvent or co-solvent is evaporated from the switching material. In other embodiments, the switching material is cured to increase the viscosity to form a gel. Curing the switching material may be accomplished with temperature, UV light, or an initiator (catalyst). Other methods of curing such as exposure to electron beams may be possible with different formulations. Cross-linking may be initiated by chemical-, thermal-, or photo-type initiators. The crosslinked switching material may adhere to both first and second substrates or layers to form an integral structure.

[00106] A composite optical filter may further comprise additional components such as tinted glass (e.g. grey, brown, bronze, reflective or other glass), static cutoff filters (coloured filters for selective transmission of visible light). In some embodiments, the composite optical filter may comprise one or more UV blocking components (a "UV blocker") to block some or a substantial amount of the UV light that the device of the invention is exposed to in order to counteract UV light-induced degradation of the switching material. The UV blocker may be incorporated in the substrate or applied as a layer on a substrate, or applied as a layer of a device according to various embodiments of the invention. The layer may be a deposited organic or inorganic material or combination thereof, or may be a film. A UV blocker may be deposited by any suitable method, for example chemical vapor deposition, physical vapor deposition, (e.g. sputtering, electron beam evaporation, and ion plating), plasma spray techniques, sol-gel processes or the like. In some embodiments, an adhesive employed to affix one or more optical filters in a composite optical filter, or to a surface may be, or comprise, a UV blocker (e.g. 8172PCL adhesive from 3M). Examples of UV blockers include W0 ₂ , W0 ₃ , ZnO, CdO or a combination thereof; thin film materials (e.g. a dichroic filter) with thickness and index of refraction chosen so as to reflect or absorb UV light; a UV absorbing polymer or a polymer comprising a light-absorbing or UV stabilizing component (which may also comprise a portion of a layer of switching material). Examples of such polymers include polyethylenes, polypropylenes, polybutylenes, epoxies, acrylics, urethanes, vinyls including polyvinyl chloride, polyvinyl butyral), polyvinyl alcohol), acetates, polystyrenes, polyimides, polyamides, fluorocarbon polymers, polyesters, polycarbonates, poly(methyl methacrylate), poly(ethyl methacrylate), polyvinyl acetate), or co-polymers or polymer blends thereof. In some embodiments, the substrate may comprise a UV blocking additive (e.g. PET XST6578 from DuPont Teijin). Such a substrate may be a UV blocking layer. In some embodiments, the substrate may have applied to one or both sides of it a UV, selective UV, IR, selective IR or selective VIS light blocking layer; the blocking layer may be in the form of a coating or film. A selective UV, VIS or IR blocking layer selectively blocks (absorbs or reflects) a portion of UV, VIS or IR light, respectively. Examples of UV blocking films that may be applied include (EnergyFilm™ (described in WO2002/018132) and EnerLogic™ (described in WO2009/087575). Examples of UV blocking layers include optically clear pressure sensitive adhesives with UV blocking components (e.g. 8172PCL from 3M). In one embodiment, the UV blocker blocks most of the light with a wavelength less than about 350 nm, or less than about 365 nm, or less than about 375 nm, or less than about 380 nm, or less than about 385 nm, or less than about 400 nm. In some embodiments, the composite optical filter comprises a switching material that is transitionable to a dark state when exposed to light with a wavelength that is greater than about 350 nm, or greater than about 365 nm, or greater than about 375 nm, or greater than about 385 nm, or greater than about 385 nm, or greater than about 400 nm. [00107] Once the individual optical filters, or the composite optical filter are assembled, they can be cut to size, and an electrical connection can be made to the electrodes (conductive layers). A perimeter seal may be applied. An electrical connection can be made by applying a bus bar onto the substrate in contact with the transparent conductive coating. Electrical leads can then be attached to the bus bars. [00108] The electrical connectors or electrical circuits of two or more optical filters may be coupled via a control system. Two or more optical filters may affixed in a composite optical filter by one or more common layers, or by an adhesive layer between two separate optical filters, or by a shared frame holding two or more optical filters adjacent to one another. In some embodiments, an composite optical filter may comprise a gap between the optical filters, such a gap may facilitate insertion or removal of an additional components such as another layer, or a light source, or may provide an insulating air gap. [00109] Electrical connectors and control circuits

[001 10] In some embodiments, a composite optical filter may comprise one or more electrical connectors, for coupling of the switching material to a voltage source. An electrical connector may comprise a bus bar. A bus bar may be applied at one edge of the optical filter and be in electrical connection with an electrode of the optical filter. Bus bars may be formed of any suitable conducting material (e.g. Cu, Au, Ag or Al foil, conductive fabric or the like) and affixed to a conductive layer of an electrode using a conducting adhesive material, for example Cu tape, polymeric glue or epoxy comprising silver (e.g. DuPont Conductor paste #4817N), a polymeric glue comprising metal (e.g. Ag, Zn, Fe, Mg, Cu, Al or the like) particles, or the like or may be printed onto a substrate (e.g. using silver epoxy or silver ink material). US 2011/0100709 describes various conducting adhesive mixtures. To affix a bus bar, a conductive adhesive may be applied to the conductive layer at a suitable location and the conductive material placed on top of the adhesive and pressed to eliminate uncontacted areas, gaps or bubbles. The adhesive may be allowed to set or cure as appropriate. [00111] Figure 6 shows a schematic diagram of a control circuit according to some embodiments. Electrodes of a first optical filter 70 are connected to a voltage regulator 76 and switch 78 via electrical connectors 72, 74. Electrodes of a second optical filter 80 are connected to voltage regulator 86 and switch 88 via electrical connectors 82, 84. Voltage regulators 76, 86 are connected to common voltage (power) source 79 via electrical connectors 89. Voltage regulators 76, 86 may be configured to provide the same, or different voltage to optical filters 70, 80. Switches 78, 88 may be operated independently, or in concert, to control the application of voltage to the optical filters 70, 80, respectively. In some embodiments, a microcontroller may be used to control the switches.

[00112] The control circuit can be used to switch the electrical voltage on or off, based on input from an automated or semi-automated device (e.g. an irradiance meter, thermometer), a building environmental control system, a user or some other input. The control circuit may modulate the applied voltage according to a predetermined level. A voltage source for operating the composite optical filter may include an AC line voltage in a house or other building, a DC power source (e.g. a battery of a vehicle, or in a separate battery or power pack), an energy harvesting power source, or the like. Examples of energy harvesting power sources include photovoltaic devices (e.g. solar cells, solar panels, or arrays thereof, photoelectric cells or arrays and the like); vibrational-energy harvesting technologies such as piezoelectric devices; mechanical energy converters such as acoustic converters; thermal energy-harvesting devices such as pyroelectric or thermoelectric devices; or the like. The one or more switches may be, for example, a transistor, a relay or an electromechanical switch. In some embodiments, the control circuit may further comprise an AC-DC and/or a DC-DC converter for converting the voltage from the voltage source to an appropriate voltage for the switching material of the composite optical filter. The control circuit may comprise a DC- DC regulator for regulation of the voltage. The control circuit may further comprise a timer and/or other circuitry elements for applying electric voltage to the optical filter for a fixed period of time following the receipt of input.

[001 13] A switch may be activated manually or automatically in response to predetermined conditions, or with a timer. For example, control electronics may process information such as time of day, ambient light levels detected using a light sensor, user input, stored user preferences, occupancy levels detected using a motion sensor, or the like, or a combination thereof, the control electronics configured to activate switches for applying voltage to the electrodes in response to the processed information in accordance with predetermined rules or conditions, or a timer. In one embodiment, the power control electronics comprises a user-activated switch that passes the DC voltage from the power source substantially directly to the composite optical filter. A user-activated switch may be a 'normally-open', or 'normally-closed' switch, for example a push-button switch. A switch may be configured to remain closed for a predetermined amount of time following actuation, thereby facilitating application of voltage to the optical filter for sufficient time to effect a state transition.

[00114] The voltage to be applied for transitioning one or more of the optical filters in an composite optical filter may be dependent on factors such as the switching material composition and/or the resistivity of the electrodes. The voltage may be fixed or it may be controllable by the control system. Voltage applied to an optical filter, or composite optical filter may be from about 0.1 V to about 20 V, or any amount or range therebetween, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19 V. In some embodiments, the amount of voltage applied is from about 0.1V to about 5V, or from about

IV to about 10 V, or from about 1.0 V to about 2.2 V, or from about 0.5V to about 3V, or from about 1.2V to about 2.5 V, or from about 1.8 V to about 2.1 V, or any amount or range therebetween. In some embodiments, the voltage applied is less than about 12 V, or less than about 6 V, or less than about 3 V or less than about 2.5 V, or about 2 V.

[00115] The polarity of the voltage applied to an optical filter assembly may be switched or alternated over a plurality of cycles to transition the assembly from a dark state to a faded state. Such polarity switching may decrease the fading time. A voltage of a first polarity may be applied across the optical filter for a first interval; followed by applying a voltage of a second, opposite polarity across optical filter for a second interval. The cycle of first and second intervals may be repeated until the optical filter is transitioned to a faded state. The first and second polarity may be of equivalent but opposite magnitude. The first and second intervals may be of equivalent magnitudes. The first and second intervals may be from about 0.5 seconds to about 60 seconds, or any amount therebetween.

[00116] In some embodiments, a switching material comprising a compound according to Formula II may be faded with application of a voltage of about 2.2V. In some embodiments, a switching material comprising a compound according to Formula I maybe faded with application of a voltage of about 2.0 V.

[00117] Preparation of optical filters

[00118] Some methods of preparing optical filters and switching material are described inWO2010/142019, and in US 61/621,736. A switching material may be coated at a suitable thickness onto a conductive coating of a substrate (e.g. ITO-coated PET) using a slot die, knife coater, roll-to-roll coating method, extrusion or the like. A second layer may be attached on the switching material - the second layer may be a transparent conductive layer, or a substrate comprising a transparent conductive material (e.g. ITO coated PET). Application of this layer may be preceded by, or followed by, a step of crosslinking or curing of the switching material. Multilayer films may be formed by co-extrusion of layers of switching material, polymers (e.g. a transparent layer according to some embodiments) or the like. The layers may be co-extruded onto opposing side of a substrate simultaneously or sequentially, or on top of one another sequentially. The first extruded layer may be cured, partially cured or uncured before application of a second layer. The substrate may be a moving web, such as in roll-to-roll manufacturing processes. Such methods may be compatible with high-volume manufacturing processes, providing an optical filter, or composite optical filter in larger sheets or rolls. 00054

[00119] The step of curing may comprise heating the composition to a temperature suitable for crosslinking (e.g. about 50 to about 90°C, or any amount or range therebetween. The step of disposing may be preceded by a step of filtration of the composition. Examples of substrates include glass or polymer films such as PET, and may further comprise a conductive coating, such as ITO; the substrate may be a moving web. The first and/or second substrates may be independently opaque or transparent, or substantially transparent.

[00120] The switching material may have a high viscosity at room temperature and may be made into a lower-viscosity liquid by heating to allow it to be applied or coated onto the substrate. In one embodiment, the switching material is heated to about 100° C and pressed between the substrates. Alternately, the switching material may be cast as a liquid and then further treated to increase the viscosity of the material to form a gel - the switching material may be dried (evaporation of a co-solvent), or a switching material comprising a crosslinkable resin may be cured to increase the viscosity to form a gel. Curing the switching material may be accomplished with temperature or UV light; other methods may be suitable with different formulations. Polymerization and/or cross-linking can be initiated by chemical- , thermal-, or photo-type initiators. The switching material may then adhere to the substrate or layers on the first or second substrates to form an integral structure. In some embodiments, components of the switching material or composition may be combined in particular order, or in particular subcombinations ('parts'), with the parts combined at a later point. Preparation of first, second and/or third parts may be advantageous to solubilize one or more components of a composition, prevent side reactions, or to prevent initiation of crosslinking ('curing') before the formulation is complete or ready for casting or coating. For example, a switching material for coating on a substrate may be prepared according to the steps of: providing a first part comprising a crosslinkable polymer, a hybrid P/E compound, an ionic material and a first portion of a solvent; providing a second part comprising an optional hardener, a crosslinking agent and a second portion of the solvent; providing an accelerant and an optional co-solvent; combining the first part and the second part; and combining the third part with the combined first and second parts. Disposition of the switching material may be performed in an environment of reduced oxygen (e.g. less than 100 ppm) and/or reduced humidity (e.g. less than 100 ppm relative humidity).

[00121] A suitable thickness may be selected such that the composition is of the desired thickness once the co-solvent is evaporated (if the switching material comprises a co- solvent), or the final layer is of the desired thickness following cooling and/or crosslinking of the coated switching material. For example, to obtain a final thickness of about 50 microns, a switching material with co-solvent may be applied to the substrate in a layer of about 100 to about 120 microns. [00122] Once the filter has been made, it can be cut to size, sealed around the perimeter if necessary, and an electrical connection can be made to the electrodes (conductive layers). The electrical connection can be made by printing bus bars onto the substrates in contact with the transparent conductive coating. In some embodiments, busbars may be printed on the substrate before disposition of the switching material, or before lamination of the substrate to the switching material. Electrical leads (electrical connectors, connectors) can then be attached to the bus bars.

[00123] Performance of optical filters may be assessed by measurement of light transmission, haze, switching speed, photostability, cycling and voltage requirements of the optical filters or components thereof. WO2010/142019 describes methods, equipment and techniques that may be used to assess the performance of optical filters. Optical filters may be useful in systems where it is desirable to dynamically control and filter light. The optical filters may be used as-is or may be laminated onto another substrate such as glass or polycarbonate. Selection of a particular set of characteristics (e.g. light transmission in the faded and dark states) may be dependent on the use of the optical filter. For example, it may be desirable for an automotive sunroof application to have an optical filter with about 5% to about 30% light transmission in the fully faded state, and opaque, or substantially opaque, in the fully dark state. The light transmission and colour of the sunroof in partially faded states (one of the two optical filters fully faded, and one dark) or one or both of the optical filters in a partially faded states, may be further selected based on user preference. [00124] In some embodiments, a composite optical filter may be disposed upon a pane of glass, or other transparent material suitable for use as a window, for a building or vehicle, or incorporation into an insulated glazing unit (IGU), or a storm window or secondary glazing. A composite optical filter may be laminated, to provide a switchable laminated glass.

[00125] The switching material may be optically clear, or may have a haze of less than about 5%, less than about 4%, less than about 3%, less than about 2% or less than about 1%. In some embodiments, the switching material has a haze of 0 to about 5% or any amount or range therebetween; or less than about 5%, about 4%, about 3% about 2% or about 1%. In some embodiments the haze is from about 0.5% to about 1%, or about 2% or about 3%. Haze may be measured, for example, using an XL-21 1 Hazemeter from B YK-Gardner, according to manufacturer's instructions.

[00126] Glass Lamination An assembly of a composite optical filter (optionally with bus bars and electrical leads attached is placed between two layers of adhesive resin (PVB or EVA sheet), and this in turn placed between two layers of glass (e.g. 3 mm float glass) The assembly may be passed through a press roll or pressed between plates at an elevated temperature (about 90°C to about 140°C - pressure and temperature may be increased and decreased over several steps), or may be placed in a bag (rubber), with an initial bonding at a temperature of about 70°C-110°C, while applying a vacuum to remove air between the layers. A second bonding step is then performed at a temperature of about 120°C-150°C, with pressure (e.g. about 0.95 to about 1.5 MPa in an autoclave). The overall thickness of the laminated glass is dependent, in part on the thickness of the various layers, generally an overall thickness of about 6.3 to about 6.6 mm is preferred.

[00127] Other layers that may be incorporated into a composite optical filter may include:

[00128] IR-blocking: One or more layers may comprise an IR-blocking component. A solar control film may be included in the multi-layer composition or laminated glass. Examples of such films include US 2004/0032658 and US 4368945. Alternately IR blocking materials may be incorporated into a layer of glass, or an adhesive layer. An IR blocking layer may reflect or absorb IR light. Reflection of IR may reduce the solar heat gain of the interior space, whereas absorption of IR may increase the temperature of the laminated glass, which may be advantageous in increasing the switching speed of the variable transmittance optical filter. [00129] UV-blocking: One or more layers may comprise a UV blocking component. Adhesive layers such as PVB may have additives that block UV (e.g. US 6627318); some transparent layers (e.g. layers 66 or 68), or some substrates (e.g. layers 54 or 56) may be made of a material that has been treated with a UV blocking material (e.g. UV-blocking PET), or have a UV blocking layer applied thereto. It may be cost effective to incorporate into the variable transmittance optical filter a substrate that blocks UV - this may be advantageous in protecting the switching material from some incident UV light. Surprisingly, the optical filter will still switch even when a UV blocking substrate that blocks a substantial portion of incident UV light of 380 nm or greater, and all UV light below about 375 nm.

[00130] Sound insulation: Sound insulation may be provided by an acoustic layer. Acoustic PVB may be known by trade names such as SAFLEX™ or VANCEVA™. US 5190826 describes composition comprising two or more layers of resins of differing polyvinyl acetals; the acoustic layer may be in the range of 0.2 to 1.6 mm. US 6821629 describes an acoustic layer comprising an acrylic polymer layer and polyester film layer. Acoustic layers comprising PVC, modified PVC, polyurethane or the like may also be used.

[00131] Self-cleaning coating: a self-cleaning coating may be applied to an outboard surface of the laminated glass, for example surface 20. Several examples of such coatings, and methods of applying them are known - examples include hydrophilic coatings based on Ti0 ₂ (e.g. Pilkington ACTIV™) and hydrophobic coatings (e.g. AQUACLEAN™ or BIOCLEAN™)

[00132] Security coating: A security coating may be applied to the laminated glass to prevent release of glass particles from laminated glass failure (breakage). Examples of such materials include PVB/PET composites or hard-coated PET films (e.g. SPALLSHIELD™ (DuPont).

[00133] Anti-scratch: an abrasion-resistant coating may be applied to the laminated glass to prevent distortion or surface damage, and preserve optical clarity; anti-scratch coatings may be particularly beneficial for use with organic glass.

[00134] Coatings or treatments applied to the inboard or outboard surfaces of laminated glass are generally optically clear. Other examples of coatings or treatments may include anti-glare or anti-reflective coatings.

[00135] Dark and faded states: Switching materials according to various embodiments may be transitioned between dark and faded states with exposure to light, and/or application nof a voltate. Both the dark and the faded states, and intermediate states of composite optical filters or the layers of switching material they include may be described with reference to colour values L*a* and b* (CIELAB coordinate system; in accordance with Illuminant D65, with a 10 degree observer, based on on CIE tristimulus values), and/or with reference to the visible light transmission LT _A (luminous transmission, Illuminant A, 2 degree observer). LTA and L*a*b* values may be measured in accordance with, for example, the SAEJ1796 standard. The L*a*b color space provides a means for description of observed color. L* defines the luminosity where 0 is black and 100 is white, a* defines the level of green or red (where + a* values are red and - a* values are green), and b* defines the level of blue or yellow (where + b* values are yellow and - b* values are blue). For example, a transmitted light described as having an L* of about 40 to about 60, an a* of about -10 to about +10 and a b* of about -10 to about

+10 (describing an area about the centre of CIELAB coordinate system) may be perceived as 'neutral', or not substantially red/green or blue/yellow. ).

[00136] A spectrophotometer may provide information concerning a materials light transmittance or absorbance at a selected wavelength or over a range of wavelengths. Absorbance and transmission of light are related through the Beer-Lambert law. Transmission spectra may be converted to an absorption profile (spectra) according using equation (1):

[00138] Absorbance values may be converted to transmission in a similar manner.

[00139] Generally, intensity of color increases with the amount of chromophore in a switching material, and LTA in a dark state decreases. Where a darker optical filter is desired, this trend may be beneficial, however reduction of the amount of chromophore may be also desirable from a cost perspective. Combining layers of switching material with transmission spectra that are complementary, to provide a colored state that is neutral, and reducing overall the total amount of chromophore in the layers of switching material may be desirable, to provide a lower-cost optical filter with the desired optical properties.

[00140] For selection of a first chromophore and a second chromophore for inclusion in first and second switching materials (respectively) of a composite optical filter, the first and second chromophores may be selected to provide a combined LTA in a dark, faded, or dark and faded state that is within parameters suitable for the intended use. Where it is desired that the composite optical filter 'black out' in a dark state, the dark state LTA may be less than 1% or 2%. Where it is desired that the composite optical filter appear neutral (without discernible color) in a dark state, the a*, b* or a* and b* may be close to zero, or the L* value may be close to about 50. First and second chromophores may be selected to have absorbance peaks sufficiently separated in the visible spectrum, that, when combined, absorb about the same amount of light across the visible spectrum, and the resulting transmitted light appears substantially uncolored, or 'neutral'.

[00141] In some embodiments, a composite optical filter may have an LTA in a dark state of about 0.5% or less, to about 20%, or any amount or range therebetween, for example 0.5, 1 , 2, 3, 4, 5, 6, 7, 8„ 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18 or 19%, or any amount or range therebetween. In some embodiments, a composite optical filter may have an LT _A in a faded state of from about 40% to about 80%, or any amount or range therebetween, for example about 45, 50, 55, 60, 65, 70 or 75% or any amount or range therebetween.

[00142] In some embodiments, transmitted light of a first optical filter (comprising a first switching material) in a dark state may be adjusted toward neutral (reduce L*, adjust a* and/or b* values of the transmitted light) by combining the first filter with a second optical filter (comprising a second switching material) of a complementary spectrum (a composite optical filter). In some embodiments, both the first and the second optical filters are transitionable between a dark and a faded state. In some embodiments, compounds (chromophores) of the first and second optical filters provide a combined transmission spectra that is 'neutral'; for example a*, b* or a* and b* values from about -20 to about +20, or any value or range therebetween; or from about -10 to about +10, or any value or range therebetween. In other embodiments, the a*, b* or both a* and b* values are from about 0 to about 10, or any amount or range therebetween. In some embodiments, the L* value may be from about 20 to about 60, or any amount or range therebetween.

[00143] In some embodiments where the composite optical filter is of very low LT _A in a dark state (e.g. less than about 2%), the L*, a* and/or b* values may be farther from neutral. At these low light transmittance, the eye may not distinguish color - a more colored state at very low LTA may be perceived as 'neutral' . Where a greater degree of light transmittance is present (e.g. from about 2% to about 20%, differences in color may be more discernible by eye, and first and second switching materials with absorbance maxima with a greater separation, and spectral overlap between the absorbance maxima may be selected. In some embodiments, the absorbance maxima (lambda max) of the first and second switching materials (first and second chromophores) may be separated by at least about 40 nm to about 150 nm, or any amount or range therebetween, or about 50, 60, 70, 80, 90, 100, 110, 120, 130 or 140 nm, or any amount or range therebetween.

[00144] Photostationary state (PSS) refers an equilibrium state of a chromophore according to Formula IA/B or Formula IIA/B (or material comprising such a chromophore) where the rate of the ring closing (forward) reaction is equal to the rate of the ring-opening or fading (reverse) reaction, when irradiated with light in a given region of the spectrum. In other words, the ratio of ring-open isoform to ring-closed isoform is at an equilibrium. PSS may be expressed with reference to a light source, or with reference to a type of light - eg. QUV, Xenon-arc lamp, Q-SU , natural or filtered sunlight, UV, VIS, IR, NIR, full spectrum, or the like, or with reference to a particular wavelength or range of wavelengths, or in the presence or absence of a filter. Table 4 sets out some exemplary PSS and absorption maxima (lambda max) for such chromophores; other chromophores (and their PSS and absorption maxima) are described in commonly-owned PCT application PCT/CA2012/000910. Some ring-open and ring-closed isomers may undergo isomerization from one to the other in response to different wavelengths of light - if a wavelength of light is used where only one of the isomers absorbs, irradiation results in complete isomerization to the other form. 254 nm, 313 nm or 365 nm light are commonly used in studies of UV-absorbing isomers, but this may not be representative of the PSS under other light conditions that include the visible spectrum such as natural or simulated sunlight ("full spectrum" light) and/or with filters that block a portion of the UV component of the light. For example, in a ring-closed (dark) state, the magnitude of the maximum absorbance in the visible range may change with the light source - the wavelength at this peak in the visible range may be referred to as lambda max, or Xmax. When full spectrum light from a solar simulator is used as a light source, a balance is achieved between the ring closed (dark) state induced by the UV component, and ring-open (faded) state induced by the visible component of the light. Inclusion of a UV blocking layer in the light path may reduce the UV component of the light, and the ring-opening reaction induced by the visible light component becomes more prominent. Different compounds may demonstrate different responsiveness to the composition of incident light. Depending on the use of a compound, one with greater or less sensitivity to light composition may be useful. This equilibrium state may be represented by an absorbance value at a particular wavelength (lambda max), and may include reference to a light source. Where desired, the ratio of ring- open and ring-closed isoforms at a PSS may be quantified by Ή NMR spectroscopy.

[00145] A sensitivity index (SI) is a ratio of the PSS under 365 nm light to the PSS under full spectrum light (without UV blocking film). SI is an indicator of the sensitivity of the compound to the composition of the incident light (a change in the ratio of UV and visible components) - photochemical ring-opening is induced by a portion of the visible light spectrum. An SI of about 1 indicates that the rate of photoconversion to the ring-closed state is about equal with both light sources, whereas as the SI increases may is indicative of a greater sensitivity to the composition of the light source (UV component).

[00146] A chromophore, or switching material comprising a chromophore, may be photofaded by exposure to visible light that is absorbed by the molecule in its dark state. The portion of the visible light spectrum that may photofade a chromophore is dependent on its absorption maxima (lambda max). Generally, a chromophore according to Formula IA/B (in a ring-closed, or dark state) may be photofaded with light in a range of from about 550 to about 690 nm. Generally, a chromophore according to Formula IIA/B (in a ring-closed, or dark state) may be photofaded with light in a range of from about 450 to about 650 nm. More specifically, a chromophore may be photofaded with light having a wavelength of about 50 nm less than to about 50 nm greater than the absorbance maxima (+/- 50 nm from absorbance maxima), or any amount or range therebetween, for example +/- 40 nm, +/-30 nm, +/- 20 nm or +/- 10 nm from the absorbance maxima. Light from a light source may be filtered to reduce transmission of wavelengths outside of the photo fading range.

[00147] In some embodiments, the ratio of the PSS for a first chromophore: second chromophore may be from about 1 : 1 to about 1 :2, to about 1 :3 or to about 1 :4, or any amount or range therebetween. In some embodiments, a compound according to Formula IA/B may have a PSS that is greater (less light transmittance at lambda max) than a compound according to Formula IIA/B. Generally, a greater absorbance at PSS may allow for a lesser amount of chromophore in a switching material; in some embodiments, a compound with a higher PSS may be preferred over one with a lesser PSS.

[00148] In some embodiments, the ratio of the SI for a first chromophore: second chromophore may be from about 1 :1 to about 1 :0.9, to about 1 :0.8, to about 1 :0.7, to about

1 :0.6, to about 1 :0.5, to about 1 :0.4, to about 1:0.3, or to about 1 :0.2, or any amount or range therebetween. In some embodiments, a compound according to Formula IA/B may have a SI that is less than a compound according to Formula IIA/B. In some embodiments, a compound with a lesser SI may be preferred over one with a greater PSS.

[00149] The term "mil" as used herein, refers to the unit of length for 1/1000 of an inch (.001). One (1) mil is about 25 microns; such dimensions may be used to describe the thickness of an optical filter or components of an optical filter, according to some embodiments of the invention. One of skill in the art is able to interconvert a dimension in 'mil' to microns, and vice versa.

[00150] As used herein, the term "about" refers to a +/- 20% variation from the nominal value. It is to be understood that such a variation is always included in a given value provided herein, whether or not it is specifically referred to.

[00151] Embodiments are illustrated, in part, by the following non-limiting methods and examples:

[00152] General methods

[001 3] Synthesis of ring-closed or ring-open isomer of compounds: Where a preparation of a ring-closed isomer is desired (as an isolated compound, e.g. for NMR studies, or some syntheses), the compound may be dissolved in CH ₂ CI ₂ and placed in a quartz glass cell. The solution was irradiated at 365 run for 10 minutes, or until no further change in absorbance is observed. Solvent was evaporated off under reduced pressure and the product purified using HPLC to afford the respective ring-closed isomer. Where a preparation of a ring-open isomer is desired (as an isolated compound, e.g for NMR studies, or some syntheses), the compound may be dissolved in CH ₂ Cl2 and placed in a quartz glass cell as described. The solution may be irradiated with visible light comprising a wavelength of -500 to 700 nm for 10 minutes, or until no further change in absorbance is observed. Solvent may be evaporated off under reduced pressure and the product purified using HPLC to afford the respective ring-open isomer.

[00154] Electrochemical switching A 1 mM solution of compound in solvent (triglyme, acetonitrile or dichloroethane) with 1% wt electrolyte (TBAPF ₆ or TBAPF4) was prepared, placed in a capillary device (50 micron wide chamber of two panes of glass with ITO-coated interior walls, separated by a circumferential bead of sealant; one of the two panes comprising two fill ports), and exposed to 365 nm UV light source until a PSS is reached. A voltage is applied to the capillary device (from 0 to about 2, or from 0 to about 2.5 volts), and the solution inspected visually for colorimetric change to a faded state, indicating the chromophore exhibits electrochemical switching.

[00155] Photostationary State (PSS Absorption spectra over the visible range (380-780 nm) were obtained using an OceanOptics™ Spectrophotometer. A 2 x 10 ^"5 M solution of compound in solvent is prepared, and photofaded using visible light until absorption in the visible region of the spectrum stabilizes. The sample is then irradiated with simulated sunlight (QSU SS-150 Solar Simulator with xenon arc lamp) until the absorption spectrum stabilizes. To obtain PSS in the presence of a UV blocking film (if desired), a second sample is prepared and irradiated as described, with a UV blocking film inserted in the light path when irradiating.

[00156] Film modeling: To obtain the scaled data for the film models, dark and light state absorption spectra were obtained using an Ocean Optics spectrophotometer as described.

[00157] The array of absorbance data (cuvette) for each wavelength (380-780 nm) integer is multiplied by a scaling ratio (equation 2)

[00158] (2) Pathcuvette ^x Conc-cuvette Pathfu _m xConc.fg _m

= Scaling ratio

MW chromophore 1 chromophore I

[00159] to provide an array of modeled film absorbance profile (equation 3):

Abs380 Abs380

[00160] (3) cuvette x Scaling ratio = film

Abs780 Abs780

[00161] The resulting array of the modeled film absorbance profile has a lambda max of the same wavelength as the cuvette data.

[00162] In some embodiments, the film thickness (film path length, or Path _film ) may be from about 0.5 mil to about 3 mil, or about 0.5, 0.75, 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8 or 3. Chromophore MW may be determined from the structure of the compound; concentration of chromophore in the film may be of any suitable value.

[00163] To model a composite filter, a first film is modeled for a desired film concentration and thickness. A second film is modeled for a selected thickness, and the concentration of the chromophore in the second film is adjusted in the formula to provide a lambda max of a similar magnitude (absorbance peak height at lambda max) as the first film. The spectra of the first film and the second film may be added together to provide a composite spectra.

[00164] Individual film spectra were obtained from single films in both dark and faded states. For a dark state spectra, films were exposed to simulated sunlight (Agro-Brite™ High output T5, 24W/6400K fluorescent lamp, Hydrofarm Agricultural Products) until a stable dark state was attained; for faded state, films were photofaded using a low-pressure sodium lamp(yellow light) until a stable faded state was attained. Transmission spectra were obtained using an Ocean Optics™ spectrophotometer.

[00165] Dark and faded states of composite optical filters were also obtained for both orientation of the composite optical filter. A composite filter with first and second optical filters was assembled and darkened in a first orientation (first optical filter closest to the light source until a stable dark state was attained, and transmission spectra obtained. The composite filter was subsequently photofaded in the same orientation, and transmission spectra obtained for the faded state. The composite optical filter was then inverted, positioning the second optical filter closes to the light source, and the filter darkened and faded, and transmission spectra obtained as described.

[00166] Example 1: Preparation of a composite optical filter

[00167] Switching material formulation comprising 84.5 wt% triglyme, 0.5 wt% TBABF ₄ , 5 wt% PMMA (10 ⁶ MW) and 10 wt% chromophore - a first switching material comprising compound S161, and a second switching material comprising compound SI 09 was prepared and placed between ITO-coated glass plates.

[00168] Optical filters were placed adjacent to one another to provide a composite optical filter, and each connected to a power source. A 365 nm light source was used to darken both switching materials. The first switching material was faded with the application of about 2.2V, while the second switching material was faded with the application of about 2.0 V.

[00169] Figure 7 shows transmission spectra over the visible light range of the composite optical filter in faded, partially faded and fully faded configurations. Where both first and second switching material are electrofaded (solid line, 110), the composite optical filter demonstrated a light transmittance of about 47%. Where only the first switching material was in the dark state (dashed line - 112), the composite optical filter demonstrated a light transmittance of about 22%. Where only the second switching material was in the dark state (dotted line - 114), the composite optical filter demonstrated a light transmittance of about 3.6%. Where both the first and second switching materials were in the dark state (dot/dashed line - 116), the composite optical filter was substantially opaque, with about 0.04% light transmittance over the visible light spectra. Note that beyond about 550 nm, the dotted and alternating dot/dash lines are overlaid.

[00170] Table 1 sets out a matrix of the dark and faded state combinations according to various embodiments. The composite optical filter may be described as having an "intermediary state" when one of the two layers of switching material is in a dark state and the other is in a faded state (thus allowing selected light transmission as described generally in Table 1).

[00171 ] Table 1. Combinations of first and second switching materials (SM), according to some embodiments.

[00172] Example 2: Composite filter

[00173] Switching material formulated as per Table 2 were prepared in three parts for separate optical filters. All mixing and coating steps were performed in an oxygen-free glove- box. A first part was prepared by combining chromophore, polymer, supporting electrolyte and a first portion of the solvent, with stirring. A second part was prepared by combining cross-linker and a second portion of the solvent. First and second parts were combined and mixed for 15-24 hours (rotating oven at 80°C). A third part comprising THF (final volume to dilute the switching material 1 :1) and accelerant was prepared. Parts 1 and 2 were combined and allowed to cool to RT; part 3 was added, and mixed at RT for ~2 hr before coating.. To prepare a layer of switching material, an ITO-coated substrate (PET) was cut to a desired shape, and the prepared formulation hand-coated (knife drawn) onto the conductive side of a first sheet of ITO-coated PET, using a coating bar. THF was evaporated, and a second layer of ITO-coated PET applied with the conductive side in contact with the switching material to form an optical filter. The switching material was allowed to cure overnight. The separate optical filters were cut to shape and assembled into a composite optical filter with an adhesive. Transmission spectra for individual films of SI 09 and SI 61 separately and as part of a composite optical filter were obtained and converted to absorbance profiles as described. Table 2 sets out the composition and thickness of the individual films; Table 3 sets out the LT _A and L*a*b* values in dark and faded states of the individual films and composite optical filters.

[00174] Table 2 : Film compositions

Table 3: Composite optical filter data. contrast Dark Faded Dark Color & Faded Color &

Film Wt%

ratio LT _A LT _A L*a*b* L*a*b*

P99 15 6 79.7 39.8,-64.3,-16.5 91.1,-13.4,30.0

JS53-68 20 55.6 79.7 72.8,33.2,40.2 90.9,-11.3,28.9

P99 (toward

light) + JS53- - 3.6 63.1 30.9,-55.4,-1 1.2 82.8,-15.2,39.4

17.5 68 (below) JS53-68

(toward light)

~ 7.7 63.1 34.3,-13.2,7.3 82.8,-15.2,39.4 + P99

8.2 (below)

P99 + JS53- 68 model - 1.4 63.6 16.8,-28.2,-9.5 83.0,-15.3,40.4

45.4 prediction

Surprisingly, the composite optical filters provide a dark state with an LT _A substantially lower than that of either filter alone. The LTA in the dark states for some embodiments may vary, depending on the orientation of the first or second filters relative to the light source. For example, where the SI 09 switching material is outboard (closer to the light source), a greater contrast ratio may be achieved, compared to the configuration where the S161 switching material is outboard. This may be due, in part to inner filtering that occurs in actual films. Advantageously, such inner filtering may be exploited to provide a composite filter that can provide more than one dark state, providing a user with additional features. It should be noted that placing the P99 optical filter closer to the light (outboard) results in a lower dark state LT _A than when the JS53-68 optical filter is placed outboard. When filter positions are reversed, decreased darkening occurs in P99 and thus it does not reach a fully dark state resulting in an increase in the dark state LT _A .

Example 3: Modeling composite filters with S109 [00176] A film of a compound according to Formula IA/B (S 109) at 1.5 mil thickness and 3wt% chromophore was modeled, and film for selected compounds according to Formula IIA/B were individually modeled and the spectra combined. Photostationary state, lambda max and sensitivity index for some first and second chromophores are set out in Table 4. Table 5 sets out the chromophores for first and second film pairings, chromophore concentration and color in the dark state.

[00177] Table 4: Characteristics of selected chromophores. Absorbance at a PSS for selected compounds was measured at 2.0 x 10 ^"5 M in triglyme in the absence (full) or presence (+UV) of a UV blocking film with a UV cutoff wavelength of 370 nm (10% transmission at 370 nm), using simulated sunlight (QSUN solar simulator) as a light source, or a 365 nm light source. All of the compounds were able to be faded by application of a voltage. SI, Sensitivity Index.

[00178] Table 5: Film combinations, wt% chromophore in first and second layers and L*a*b* values of modeled composite filter when both first and second layers are in a dark state. The LT _A for the dark and faded states of the individual chromophores at the modeled wt% is provided, along with the LT _A in dark and faded states for the modeled composite filter. SI 09 modeled at 3 wt% has a dark state L*a*b* of 59.6,-52.4,-8.7, and a faded state L*a*b* of 89.4,-7.9,12.7. The dark and faded LT _A for a 3% S109 layer is the same for all pairings in Table 5.

Combined Spectra

Chromophore pairings

Wt%

(Dark LT _A Faded LT _A ) Dark Faded Dark State Faded State

LT _A LT _A L*a*b* L*a*b*

SI 09 (20.4/74.9) 3

11.6 67.7 39.2,-6.7,27.4 82.4,4.2,44.2 S079 (63.9/68.2) 57

S109 3

5.1 55.1 26.9,11.4,-13 81.1,36.7,-54.9

S083 (41.6/55.7) 41

S109 3

3.6 66.6 23.3,-15.1,10 83.6,-9.5,44.9

S137 (17.5/67) 16.5

S109 3

8.2 66 32.4,9.5,9.4 84.1,-13,39

SI 40 (55.9/66.5) 14.7

S109 3

4.4 54.9 24.8,0,0.7 77.9,-13.5,45.6

SI 44 (26.6/55.3) 7.3

S109 3

5.7 57.6 27.9,1.6,3.2 79.8,-8.7,26.5

SI 51 (34.1/58.0) 7.1

S109 3

4.7 39.1 23.6,2.6,92.6 62.4,24.5,150.8

SI 52 (31.1/39.4) 9

S109 3

4.8 64 25.9,3.3,-0.2 82.6,-7.5,35.9

SI 55 (31.1/64.4) 10

S109 3

6 49.1 28.5,4.1,3.9 75.2,-1 1.4,25.2

SI 61 (37.9/49.4) 10.4

S109 3

5.5 47.9 27.5,3.2,-0.1 74.6,-10.2,18.6

SI 62 (34.1/48.2) 7

S109 3

3.1 72.5 25.5,-2.3,-29.1 87.9,-10.8,23.4

S163 (19.4/73) 3.8

S109 3

3.6 73.4 27.2,1.2,-31.6 88.6,-12.9,23.3

SI 64 (23.7/73.9) 3.4 Example 4: Modeling composite filters with S158

[00179] A film of a compound according to Formula IA/B (SI 58) at 1.5 mil thickness and 3wt% chromophore was modeled, and film for selected compounds according to Formula I1A/B were individually modeled and the spectra combined. Table 6 sets out the chromophores for first and second film pairings, chromophore concentration and color in the dark state. Photostationary state, lambda max and sensitivity index for some first and second chromophores are set out in Table 4.

[00180] Table 6: Film combinations, wt% chromophore in first and second layers and L*a*b* values of modeled composite filter when both first and second layers are in a dark state. The LT _A for the dark and faded states of the individual chromophores at the modeled wt% is provided, along with the LTA in dark and faded states for the modeled composite filter. SI 58 modeled at 3 wt% has a dark state L*a*b* of 57.9,-57.6,-8.6, and a faded state L*a*b* of 87,-13,27.2. The dark and faded LT _A for a 3% SI 58 layer is the same for all pairings in Table 6.

S158 3

3.9 51.8 22.8,1.6,4.1 76.1,-10.6,36.7

S151 (30.7/55.3) 8.4

S158 3

3 32.9 18,4.3,84.9 57.4,28.5,147.8

S152 (27.4/ 35.1) 11

S158 3

3.3 58.9 20.8,3.2,0.2 79.5,-8.2,45.2

SI 5 (28.0/62.8) 11.7.

S158 3

4.3 43.1 23.6,4,4.7 71.1,-13.6,34.4

S161 (35.2/46.0) 12.2

S158 3

3.8 41.6 22.3,3.3,0.6 70.2,-12.8,27.8

SI 62 (30.8/44.4) 8.3

S158 3

2 68.1 20.7,-2.3,-29.4 85.4,-14.1,35.7

S163 (16.5/72.6) 4.5

S158 3

2.3 69 22.2,1.7,-32.2 86.2,-16.6,35.6

SI 64 (20.8/73.6) 4.1

[00181] As demonstrated in the above examples, an individual switching material with a single chromophore at the indicated wt% demonstrates a difference in light transmittance between dark and faded states, but the contrast ratios (faded state: dark state) may vary. To provide a balanced (substantially neutral) color, the quantity of the chromophore (according to Formula IIA/B) in the second switching material may be selected to provide an absorption peak at lambda max of about the same magnitude of that of the first switching material (SI 09 or SI 58 as per these examples). For some second switching materials, this quantity may be over 50 wt% in some examples. [00182] Other Embodiments

[00183] It is contemplated that any embodiment discussed in this specification can be implemented or combined with respect to any other embodiment, method, composition or aspect, and vice versa. Figures are not drawn to scale unless otherwise indicated.

[00184] The present invention has been described with regard to one or more embodiments. However, it will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Numeric ranges are inclusive of the numbers defining the range. In the specification, the word "comprising" is used as an open-ended term, substantially equivalent to the phrase "including, but not limited to," and the word "comprises" has a corresponding meaning. As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Citation of references herein shall not be construed as an admission that such references are prior art to the present invention, nor as any admission as to the contents or date of the references. All publications are incorporated herein by reference as if each individual publication was specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.