Highly transparent electrochromic coating material, method for producing the same and use of the material

The invention relates to a method for the preparation of a novel hybrid electrochromic coating material with superior performance in terms of transparency, electrochromic contrast, colouration efficiency, and adhesion, for a use in electrochromic devices for applications where a high transparency is required in the bleached state.

Background of the Invention

Since the discovery of inherently conductive polymers (ICP) , there is huge interest in their use for a variety of applications. Thin films of ICP gain electrical conductivity by oxidation (p-doping) or reduction (n-doping) usually accompanied by the insertion of anionic or cationic species to assure charge neu-

trality. The charge carriers formed are able to move along the π-conjugated carbon double bonds of the polymer backbone, which imparts to the polymeric material an intrinsic electronic conductivity (S. Sadki, P. Schottland, N. Brodie, G. Sabouraud, Chem. Spc. Rev. 2000, 29, 283) .

All ICP are potentially electrochromic, i.e., able to change their absorption characteristics depending on their redox state. One possible field of application for ICP are therefore electrochromic devices (ECD) , i.e. smart, switchable devices that are able to undergo electrochemically reversible colour changes and allow a deliberate power-triggered reduction of light transmittance whenever needed. ECDs usually consist of two complementary electrochromic materials, contacted by metallic or oxidic conductors with an electrolyte inbetween (D. R. Rosseinski, R. J. Mortimer, Adv. Mater. 2001, 13, 783). Since one of the electro- chromic materials is anodically colouring while the other changes its colour cathodically, they behave together as a redox pair, and, after application of a potential, high contrasts may be achieved. There have been many efforts in the past to utilise ECDs for eye protection and light transmittance control systems.

However, though some ECDs based upon inorganic oxides or organic dyes show good performance, there are still major disadvantages obstructive to a broader exploitation. In particular, a technology is lacking to produce cost-effective, battery-driven plastic

ECDs with an uncoloured, highly transmittive bleached state and a strong electrochromic contrast.

Poly (3, 4 -ethylene dioxythiophene) (PEDOT), a well known π—conjugated conductive polymer, shows a fairly high transparency in its oxidised state, and compared

to other conductive polymers, it is more environmentally stable. Due to its remarkable properties, it has been suggested for a couple of applications, among them being electrochromic devices as well (H. W. Heuer, R. Wehrmann, S. Kirchmeyer, Adv. Funct . Mater. 2002, 12, 89). However, regardless of the type of preparation (by electropolymerisation, chemical oxidative polymerisation, or from polymer dispersions) , PEDOT films always show a sky-blue colour in their oxidised (bleached) state, which is not acceptable for applications where a "water-clear" appearance is needed. Studies performed to enhance the transparency of PEDOT films (Y. -H. Ha, N. Nikolov, S. K. Pollack, J. Mastrangelo, B. D. Martin, R. Shashid- har, Adv. Funct. Mater. 2004, 14, 615) were targeted to decrease the coating thickness rather than the absorption.

A versatile derivative of 3, 4 -ethylene dioxythiophene (EDOT) is "EDOT-MeOH" (also called Baytron M-OH) , a hydroxyfunctional derivative of the parent EDOT monomer. In-situ polymerised films derived from EDOT-MeOH have been suggested for a use in capacitors (U. Merker, K. Reuter, K. Lerch (Bayer Chemical Corp.), US 2004/0085711 Al, 2004) . Though these films show optical properties very similar to PEDOT films, the monomer is capable of being functionalised and shows enhanced solubility in water.

The band gap (i.e. the electro-optical properties) and conductivity of conducting polymers can be controlled by proper choice of substituents, (G. Pagani . A. Berlin, A. Canavesi, G. Schiavon, S. Zecchin, G. Zotti, Adv. Mater 8 (1996) 819, and references therein) , thus opening ways to more transmittive systems. Moreover, with regard to electrochromic de-

vices, a method is required to ensure durable adhesion of the organic polymer films on the contacting transparent electrodes that are preferably of inorganic nature. The present invention picks up on these points.

A large number of publications are available dealing with several aspects of poly (alkylene dioxythiophene) based materials. Only some selected articles or pat- ents shall be mentioned here.

The chemical oxidative polymerisation of substituted poly (alkylene dioxythiophene) s to thin films for a use in electrolyte capacitors was described in US 2004/0085711 Al/ EP 1 391 474 (Bayer Corp.). The polymers claimed comprised alkyl, aralkyl, aryl or cycloalkyl end groups .

US 2005/0129857 Al describes a chemical polymerisa- tion procedure for highly conducting and transparent

EDOT films using imidazole as the moderator base. Thereby, the transparency depended on the coating thickness .

The chemical oxidative polymerisation of EDOT and the properties of the resulting polymer was described in Synth. Met. 101, 1999, 561-564 and Synth. Met. 149, 2005, 169-174.

The synthesis by chemical polymerisation using ferric chloride in dry chloroform of a series of soluble alkyl derivatised poly (alkylene dioxythiophene) s were described in Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) 37(2), 1996, 337.

A preparation route for hydroxyraethyl substituted EDOT and electrochemical polymerisation thereof was described by Welsh, Dean M. et al. in Polymer Preprints (American Chemical Society, Division of PoIy- mer Chemistry) (1997), 38(2), 320.

The synthesis of EDOT derivatives with hydroxymethyl or methoxyethoxyethoxymethyl groups as well as the effect of substituents on the band-gap level was de- scribed in Electrochemistry Communications (2000) , 2 (1) , 72-76.

In Polymer Mater. Sci . Eng. (2002), 86, 55-56, the electrochromism of poly (bis (3 ^v -methyl) -3 , 4-propylene dioxythiophene) (PProDOT-Me2) , poly (3 , 4 -ethylene di- oxythiophene) (PEDOT), poly- (3 , 6-bis (3 , 4-ethylene di- oxythienyl) -N-methylcarbazole) (PBEDOT-NMeCz) , poly (3, 4 -ethylene dioxypyrrole) (PEDOP), poly(3,4- propylene dioxypyrrole) (PProDOP) , and their N- substituted analogues were investigated with regard to a use in ECDs .

In Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (1999), 40(2), 1206, the synthesis and electropolymerisation of substituted 3, 4 -propylene dioxythiophene (ProDOT) derivatives were reported.

A synthesis route for dimethylated poly (3 , 4 -propylene dioxythiophene) (PProDOT) for electrochromic devices was described in Advanced Materials (Weinheim, Germany) (1999), 11(16), 1379-1382. Electrochromic devices based on poly (3 , 4 -propylene dioxythiophene) derivatives were proposed in Proceedings of SPIE-The International Society for Optical Engineering (2002), 4695 (Electroactive Polymer Actuators and Devices

( EAPAD) ) , 442 -450 .

An article in Synthetic Metals (1999), 102(1-3), 967- 968 deals with the electrochemical synthesis of a se- ries of poly (3 , 4-alkylene dioxythiophene) s using 3,4- alkylene dioxythiophene derived monomers where either the size of the alkylene dioxy ring or the nature of the pendant group was varied.

In Chemistry of Materials (1998), 10(3), 896-902, the electrochemical synthesis of Poly (3 , 4-alkylene dioxythiophene) derivatives from (3 , 4 -ethylene dioxythiophene (EDOT), 2-methyl-2, 3-dihydrothieno [3, 4-b] [1,4] - dioxine (EDOT-Me), 2-tetradecyl-2 , 3-dihydrothieno- [3, 4-b] [1,4] dioxine (EDOT-C14H29) , 2-phenyl-2 , 3-dihydrothieno [3 , 4-b] [1, 4] dioxine (EDOT-Ph), 3,4-di- hydro-2H-thieno[3,4-b] [1,4] dioxepine (ProDOT) , 3- methyl-3 , 4-dihydro-2H-thieno [3 , 4-b] [1, 4] dioxepine (ProDOT-Me), 2 , 3 , 4 , 5-tetrahydrothieno [3 , 4-b] [1,4]- dioxocine (BuDOT), and 5 , 10-dihydrobenzo [f] thieno-

[3, 4-b] [1, 4] dioxocine (BuDOT-XyI)) was described. The materials were claimed to be fast electrochromics with high contrast ratios .

Electrochemically prepared electrochromic polymers including alkyl derivatives of poly (3 , 4 -ethylene dioxythiophene) and derivatives of bis (3 , 4 -ethylene dioxy) arylenes are briefly discussed in Polymer Preprints (American Chemical Society, Division of PoIy- mer Chemistry) (1996), 37(1), 135.

DE 101 62 746 deals with a process for the production of 5-alkyl dioxeno [2 , 3-c] thiophenes via transetheri- ficative cyclocondensation of 3 , 4-dialkoxythiophenes with vicinal alkanediols.

The manufacture of alkylene dioxythiophene dimers and trimers as precursors for conductive polymers was described in EP 1 375 560.

U.S. Pat. Appl. US 6,747,780 (2002) comprises elec- trochromic organic polymer syntheses and devices (e.g. surface plasmon resonance imaging systems, electrochromic windows, and ECD) utilizing electro- chromic organic polymers . Laminated electrochromic devices with a cathodic polymer (e.g., poly [3 , 3-dime- thyl-3,4-dihydro-2H-thieno[3,4-b] [1 , 4] dioxepine] ) layer; a solid electrolyte layer; and a counter electrode layer are described. An anodic polymer layer (e.g. , poly (3 , 6 -bis (2- (3, 4-ethylenedioxythiophene) ) - N-methylcarbazole) ) may be formed on the electrolyte layer under the counter electrode.

In PCT Int. Appl. (2003), 150 pp. (WO 03046106), electrochromic polymers including substituted poly (3 , 4 -ethylene dioxythiophene) are described for a use in electrochromic device applications.

In Chemistry of Materials (2004), 16(12), 2386-2393, the authors report on the use of highly porous mem- branes which allow the production of patterned, rapid- switching, reflective ECDs. As the active EC materials, they used poly (3 , 4 -ethylene dioxythiophene) (PEDOT), poly (3 , 4 -propylene dioxythiophene) (PProDOT) , and the dimethyl-substituted derived PPro- DOT-Me2.

Several methods to pattern conducting polymers to build ECDs and multi-colour displays, which are made possible through patterning of electrode surfaces, were published in Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (2004) ,

45 ( 1 ) , 169 .

Exemplary for di-Me substituted poly (propylene di- oxythiophene) (PProD0T-Me2) films, electrochemical and spray coating techniques to deposit electrochro- mic polymers onto porous metallised membranes which are used to construct reflective type polymer elec- trochromic devices were described in Polymeric Materials Science and Engineering (2004), 90, 40.

In patent application U.S. Pat. Appl . Publ . (2002), 29 pp. US 6,747,780, laminated electrochromic devices are described which comprise a transparent electrode layer; a cathodic polymer (e.g., poly [3 , 3 -dimethyl- 3, 4-dihydro-2H-thieno [3 , 4-b] [1, 4] dioxepine] ) layer; an electrolyte layer comprising a solid electrolyte; and a counter electrode layer. An anodic polymer layer (e.g., poly (3, 6-bis (2- (3 , 4-ethylene dioxythio- phene) ) -N-methylcarbazole) ) may be formed on the electrolyte layer under the counter electrode.

In Advanced Materials (Weinheim, Germany) (2001) , 13(9), 634-637, the authors describe the optimisation of electrochromic devices that operate in the reflec- tive mode and are able to modulate the reflectivity in the visible, near-IR and mid-IR regions of the electromagnetic spectrum. The used electrochromic material was PProDOT-Me2.

An ECD application using the electrochromic polymers poly [3 , 3 -dimethyl -3 , 4-dihydro-2H-thieno (3,4- b) (1,4) dioxepine] (PProDOT- (CH ₃ ) ₂ ) and poly [3 , 4- (2 , 2- dimethylpropylene dioxy) -pyrrole] (PProDOP- (CH ₃ ) ₂ ) was described in: Proc . SPIE - The International So- ciety for Optical Engineering (2003) , 5051 (Electro- active Polymer Actuators and Devices (EAPAD) ) 404-

411 .

WO 02/079316 describes the application of aqueous compositions containing 3,4-dialkoxy thiophene poly- mers and non-newtonian binders for electrochromic devices.

None of the described electrochromic polymers and devices apparently fulfils the requirements in terms of transparency in the bleached or oxidised state for applications where a highly transmittive state is required. Information about the durability and environmental stability of the polymer films or devices is given in only a few cases . Poor adhesion at the in- terfaces of polymer and inorganic oxide layers turned out to be a common reason for poor cycle stability (delamination upon electrochemical cycling) .

It has been found that the polymeric materials claimed by other authors or inventors to have at least one colourless (or nearly colourless) state do not comply with transparency requirements for ophthalmic and automotive applications or articles. For instance, PEDOT (which is usually claimed to be col- ourless in its oxidised form) shows a light blue colour at coating thicknesses in the range of several hundred nanometres. Going to thinner films results in higher transparency, but lower electrochromic contrast, thus, is not supposed to be useful.

In cases where a real colourless state has been reported (B. C. Thompson, P. Schottland, K. Zong, J. R. Reynolds, Chem. Mater, 2000, 12, 1563), the authors operated with variable potentials in order to have intermediate oxidation states. This cannot be done with a battery providing a single definite voltage.

To work at fixed potentials is a considerable improvement in relation with the necessity of intermediate oxidation states and the need of tuning the potential .

A further drawback was identified in that polymeric thin films prepared by in-situ chemical polymerisation suffer from poor adhesion on transparent conducting oxides. This becomes particularly evident during the rinsing step being an essential part of the in-situ polymerisation procedure where delamina- tion of the polymer films frequently and readily occurred.

The fact that electrochromic polymer films deposited on inorganic surfaces - presumably due to what is outlined in the previous section — easily delaminate upon continuous potential cycling in liquid or semi- liquid electrolytes was considered to be a further drawback. This phenomenon has been described several times in literature and was recently confirmed by own investigations .

Therefore, it is an object of the present invention to provide a method which allows the preparation of a highly transparent electrochromic coating material with improved adhesion performance, thus avoiding the problems known from the state of the art .

This object is achieved by the method given with the features of claim 1 and the coating material given with the features of claim 24. Possible uses of the coating are named in the claims 37 to 48. Herein, the depending claims describe preferred embodiments, re- spectively.

According to the invention, a method for preparation of a electrochromic coating material is provided by subsequently performing the following steps :

a) reaction of a solution comprising a mixture of a compound having the general formula I and a compound having the general formula II in a molar ratio of I : II which is equal to m : (100-m) wherein m has a value from 60 to 99

formula I formula II

with a compound of the general formula III

formula III

wherein X is selected from the group consisting of Y-, Y-C(O) - or OCN-

in which Y is selected from the groups of halides, mesylates and/or triflates,

R is a linear and/or branched alkylene chain with 1 to 16 carbon atoms, and

A is a linear and/or branched alkyl chain with 1 to 16 carbon atoms or hydrogen

b) further reacting the mixture of compounds derived from step a) by either

bl) a vinyl copolymerisation

b2) a hydrosilylation of the vinyl moiety with a si- lane of the general formula HSiR' _u (R' ' ) ₃ - _U/ wherein R' is selected from the group consisting of linear or branched alkyl or alkenyl chains with 1 to 12 carbon atoms in the main chain, wherein the chains can be substituted with acryloxy-, methacryloxy- , succinyl-, amino-, hydroxyl-, mercapto-, and/or glycidoxy groups and/or interrupted by O- and/or S-atoms and/or a NR- group ,

R' ' is selected from the group consisting of halogens, hydroxyl -groups, alkoxy-groups and/or acyl- groups with 1 to 4 carbon atoms, and u = 0, 1, 2, 3; and further

b3 ) a thiol -ene addition to the vinyl moiety with a compound of the general formula HS-R-SiR' _u (R' ' ) ₃ -u, wherein R, R' , R' ' and u have the same meaning as indicated above;

c) in-situ chemical oxidative polymerisation of a solution of the compound and/or the compounds derived from step b) .

For enhancement of the reactivity of the compound with formula III, the double bond is preferably, but not exclusively a terminal double bond. Generally speaking, in step b) , a reaction with compounds that upon hydrolysis or polycondensation impart sol-gel-

processability to the whole system is carried out.

It is preferred, if m has a value from 70 to 95.

In an improved embodiment, in step a) a base selected from the group of aromatic and/or aliphatic nitrogen containing compounds is used in a stochiometric or sub-stochiometric ratio. The scope of the aromatic nitrogen containing compounds is not limited, yet it is advantageous if the base is selected from the group consisting of pyridine, 4- (dimethylamino) - pyridine, triethylamine and/or mixtures thereof.

Preferably, in step a) a solvent, selected from the group consisting of acetonitrile, dichloromethane, toluene, 1,4-dioxane and mixtures thereof is used.

Furthermore, it is advantageous if in step a) the reaction mixture is heated to reflux condition of the according solvent.

The additional reaction step b) can be preferably carried out in situ, which simplifies the whole procedure of synthesis.

In a further preferred embodiment, in step bl) the mixture of compounds derived from step a) is copoly- merized. This is to understood that the compounds derived from step a) (which now bear the reactive vinyl moiety) are polymerized by methods known to those skilled in the art. These methods include but are not exclusively limited to radical polymerisation. According to this embodiment, a copolymer is derived from step bl) .

In an alternative preferred embodiment, before the

copolymerisation of step bl) is undertaken further a alkenyl functionalized silane of the general formula CH ₂ =CH-R-SiR' _u (R' ' ) ₃ -u, wherein R, R' and R'' have the same meaning as indicated above, is added as further monomer to the mixture of compounds derived from step a) . This alkenyl functionalized silane can be added in stochiometric, substochiometric or supersto- chiometric amounts. As already mentioned, the methods for this kind of copolymerisation are known to those skilled in the art. Insofar, in step bl) , primarily a mixture of compounds comprising the coupling products of the alkenyl functionalized silane with the products to arrive from step a) are obtained.

Moreover, it is preferred if in step c) a primary and/or secondary aliphatic alcohol with 4 to 8 carbon atoms or mixtures thereof is used as solvent. It has been shown that positive effects can be achieved, if additionally at least one aprotic solvent with a high boiling point is used. By high boiling point, a temperature of at least 100 ⁰ C is understood. Preferably, the at least one aprotic solvent is selected from the group consisting of dimethylsulfoxide (DMSO) , dimethylformamide (DMF) , N-methylpyrrolidone (NMP), propylene carbonate, dioxane , 2- methylethylether (diglyme) , hexamethylphosphoramide, sulfolane or mixtures thereof.

In addition, it is preferred if in step c) a modera- tor, selected from the group consisting of amino bases with primary and/or secondary amino functionalities is used. The moderator is preferably selected from a mono-, bi- or tridentate amine, which in addition to that can also possess a silyl functionality. In a special embodiment, the moderator comprises at least one aminosilane, in particular selected from

the group consisting of 3-aminopropyl trimethoxysi- lane, 11-aminoundecyl triethoxysilane, m- and/or p- aminophenyl trimethoxysilane, 3- (atninophenoxy) propyl trimethoxysilane, 3-aminopropylmethyl diethoxysilane, 3-aminopropyldimethyl ethoxysilane, 3 -aminopropyl- diisopropyl ethoxysilane, N- (2-aminoethyl) -3 -amino- propyl trimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyl dimethoxysilane, N- (2-aminoethyl) -3-amino- isobutylmethyl dimethoxysilane, N- (2-aminoethyl) -11- aminoundecyl trimethoxysilane, N- (2-aminoethyl) -3- aminoisobutyldimethyl methoxysilane, N- (2-aminoethyl) -3-aminopropyl silanetriol, N- (6-aminohexyl) -3- aminomethyl trimethoxysilane, N- (6-aminohexyl) -3- aminopropyl trimethoxysilane, 3-aminopropylsilan- etriol . Above all, 3-aminopropyl triethoxysilane, 4- aminobutyl triethoxysilane and N- (2-aminoethyl) -3- aminopropyl triethoxysilane are preferred. The reagents of choice are 3-aminopropyl triethoxysilane, 4-aminobutyl triethoxysilane and N- (2-aminoethyl) -3- aminopropyl triethoxysilane.

Generally, the temperatures at which the method is carried out is not limited to a special range, yet it is preferred if the temperature in step b) is ad- justed between -40 and +30 ⁰ C, preferably between -20 and +5 ⁰ C.

In a further preferred embodiment, a organo silicon component is added in step b) . Preferably this compo- nent is of the general formula R' _x Si (R' ' ) _4-x , wherein R' and R' ' have the same meaning as indicated above and x = 0, 1, 2, 3, 4. Again, the added silicon component can be added in either substochiometric, sto- chiometric or superstochiometric ratios. These or- ganosilicon compounds may act as graftable compounds and adhesion promotors .

Optionally, further functional sol-gel-processable organosilicon compounds as cross- linkers and network modifiers can be added.

The mentioned organosilicon compounds serve to

• improve the adhesion on transparent conducting oxides or other oxidic substrates, • cross- link by poly-condensation reactions the ingredients of the material,

• act as network modifiers.

They comprise organo (alkoxy) silanes, or- gano (alkoxy) silane pre-hydrolysates , organosilanols and organopolysiloxane pre-condensates . The sol-gel process may be performed prior to or simultaneous with the in-situ polymerisation.

The special advantage of the method according to the invention is, that the chemical oxidative polymerisation as claimed in step c) can be carried out in situ. Preferably, the polymerisation is performed by adding at least one oxidant selected from the group consisting of iron- (III) -salts, hydrogenperoxide, di- chromates, peroxodisulfates, perchlorates, persul- fates, perborates, permanganates and/or mixtures thereof. Among the iron- (III) -salts, the following compounds are especially preferred: iron- (III) -chlo- ride, iron- (III) -sulfate, iron- (III) -perchlorate, iron- (III) -alkylsulfonates , iron- (III) -carboxylate, iron- (III) -dodecylsulfonate, iron- (III) -salts of aromatic sulfonic acids, e.g. iron- (III) -benzenesulfo- nate and/or mixtures thereof. Iron- (III) -p-toluene- sulphonate is the reagent of choice.

Moreover, it is of advantage that in step c) additionally at least one compound derived from step a) is added.

Additionally, also a colour modifier selected from the group consisting of arylhydrazones of dyes constituted by an aromatic and/or heteroaromatic unsaturated core, end-capped with either electrochemically or chemically polymerogenic units or alternatively with alkoxysilane chains can be added. This addition can be carried out in each of the steps a) to c) . The colour modifier is capable of colour switching upon redox cycling and is apt to correct the blue colour of the neutral basic electrochromic system.

According to the invention, also an electrochromic coating is provided comprising the units according to the following general formulae IV and V

formula IV formula V

wherein

Z is selected from the group consisting of the structural elements -R-, -C(O)-R- and -C(O)-NH-R-, wherein R is a linear and/or branched alkylene chain with 1

to 16 carbon atoms,

D is selected from the group consisting of -SiR' _u (R' ' ) ₃ - _u , -S-R-SiR' _u (R' ' ) _3-u , and R has the same meaning as indicated above,

R' is selected from the group consisting of linear or branched alkyl or alkenyl chains with 1 to 12 carbon atoms in the main chain, wherein the chains can be substituted with acryloxy- , methacryloxy- , succinyl-, amino-, hydroxyl-, mercapto- , and/or glycidyloxy- groups and/or interrupted by O- and/or S-atoms and/or a NR-group, wherein R has the same meaning as indicated above, R' ' is selected from the group consisting of halo- gens, hydroxyl-groups, alkoxy-groups and/or acyl- groups with 1 to 4 carbon atoms, and u = 0, 1, 2, 3; or alternatively represents a chemical bonding to corresponding positions D of neighboured monomers, of the formulae IV and/or V,

A is a linear and/or branched alkyl chain with 1 to 16 carbon atoms or hydrogen, and

the compounds of the general formulae IV and V are comprised in a molar ratio of IV : V = m/(100-m) , wherein m has a value in from 60 to 99.

In a preferred embodiment, m is selected from 70 to 95.

The material according to the invention shows a lot of advantages. One advantage is that the necessary time to induce a colour change upon oxidation or re- duction is less than 3 seconds, preferably less than 2 seconds . These very short reaction times open a

wide field of applications.

Furthermore, a material according to the invention shows high mechanical and/or photochemical stability and integrity.

Yet, another advantage of the coating according to the invention is that it possesses excellent adhesion behaviour towards glass, organic polymers or metal oxide surfaces, preferably transparent conducting oxides, especially preferred tin-doped indium oxide (ITO) , fluorine-doped tin oxide (FTO) , aluminium- doped zirconium oxide (AZO) , antimony-doped tin oxide (ATO) , antimony/tin-doped zinc oxide (ATZO) and in- dium/tin-doped zinc oxide (ITZO) .

The coating according to the invention also shows a high contrast which can be more than 50 % in the visible range of the electromagnetic spectrum at the wavelength of maximal absorption.

The thickness of this coating can be selected pending on the use the coating is intended for and is thus not limited. Preferably, the thickness of the coating is within the range of 10 nm to 1000 nm, preferably of 100 nm to 500 nm, especially preferred of 150 nm to 250 nm.

The coating according to the invention possesses in- creased chemical stability and resistance against decomposition. It was shown that the material according to the invention shows a decrease in absorption of less than 20 %, preferably, less than 15 % after 1000 redox cycles of electrochemical switching in liquid electrolyte under ambient conditions.

Preferably, the transmittance of the coating with a thickness of 200 nm in the visible range of the electromagnetic spectrum is above 80 %.

Additionally, colour modifiers can be comprised within the coating. These colour modifiers are preferably selected from the group consisting of arylhy- drazones of dyes constituted by an aromatic and/or heteroaromatic unsaturated core, end-capped with ei- ther electrochemically or chemically polymerogenic units or alternatively with alkoxysilane chains.

The coating can comprise additional compounds . For example, additionally an organo silicon compound of the general formula R' _x Si (R' ' ) _4-x is comprised, wherein

R' and R' ' have the same meaning as mentioned above and x = 0, 1, 2, 3, 4.

In another aspect of the invention, the coating according to the invention can be obtained by the method described above. Therefore, it is preferred, if compounds prepared according to steps a) , b) or c) are used for the preparation of thin primer films in order to establish strong adhesion between the in- situ polymerized films resulting from step c) and the substrate they are applied to.

It is also according to the invention, that a use for the coating is given.

According to the invention, the coating can be used for coating a surface of a substrate, whereas the substrate is especially selected from the group con- sisting of glasses, plastics, metals, transparent conductors and metal oxides. Optionally the sub-

strates can be coated with thin layers of conducting oxides (e.g. IZO, FTO, etc.) and/or conducting polymers (e.g. Poly- (3, 4-ethylendioxythiophene) ) which can be obtained starting from products such as Bay- tron P (by H. C. Starck) .

The surface of the substrate is not limited to a special shape, i.e. the surface of the substrate can be flat or have a curvature (e.g. being convex or con- cave) .

Preferably, the coating material can be applied to a substrate by administering compounds prepared according to Steps (a) , (b) or (c) by preparation of thin primer films in order to establish strong adhesion between the in- situ polymerized films resulting from Step (c) and the substrate.

Preferably, the coating is applied to the substrate by means of spin coating, doctor blade coating, spray coating and/or roll-to-roll coating.

In addition to that, it has been shown to be positive if after application the coating is cured.

The curing of the coating can be accomplished by applying a radiation of any region of the electromagnetic spectrum including IR- to UV-radiation, heating to temperatures above 60 ⁰ C, via curing by electron- beam and/or via curing by plasma.

It is preferred, if after curing the coating is rinsed. The rinsing agent is not limited to any substance but is preferably selected from the group con- sisting of a primary and/or secondary aliphatic alcohol with 4 to 8 carbon atoms, dimethylsulfoxide

(DMSO) , dimethylformaraide (DMF) , N-methylpyrrolidone (NMP), propylene carbonate, dioxane, 2-methylethyl- ether (diglyme) , hexamethylphosphoramide, sulfolane and/or mixtures thereof. After rinsing, the coating can be dried.

A preferred use for the coatings is for electrochro- mic devices.

The coating also can be used for antistatic and/or electrodissipative equipment of surfaces, which can belong to plastic parts, textiles and/or fabrics.

In yet another embodiment, the coating can be used for corrosion protection of metal surfaces.

Also the use of the coating according to the invention for optical lenses, glasses and/or ophthalmic applications is preferred.

The present invention is further illustrated in detail by the following examples and figures. Yet the invention is not limited by the hereinafter mentioned special embodiments .

The figures show:

Fig. 1 shows the functionalisation of the pristine polymerogenic units to improve adhesion by sol-gel type processes.

Fig. 2 shows the comparison of the effect of the length of the alkyl chain on the transparency in reduced and oxidised state of PoIyEDOT-MeOH (—) vs. Poly SE-EC5( ) vs. Poly SE-ECIl (- ^• -),

Fig. 3 shows the standard system switching time between the oxidised/reduced states.

Fig. 4 shows the typical stability of an SE-ECIl coating after 1000 redox cycles of electrochemical switching in a liquid electrolyte (10 s at + 1.0 V) .

Synthetic Procedures

Details on the monomer system

The polymerogenic units were obtained starting from hydroxyfunctional 3 , 4-ethylenedioxythiophene derivatives, preferably, but not exclusively as the mixture described by Bayer (U. Merker, K. Reuter, K. Lerch (Bayer Chemical Corp.), US 2004/0085711 Al, 2004). The constituents of the original mixture (hereinafter abbreviated by SE) were 2-hydroxymethyl-2, 3-dihydro- thiene [3 , 4-b] [l,4]dioxine (usually named (2-hydroxy- methyl) -3 , 4-ethylenedioxythiophene or hydroxymethyl

EDOT or else EDOT-MeOH) (80 %) and 3 , 4-dihydro-3 - hydroxy-2H-thieno [3, 4-b] [1, 4] dioxepine (usually named 3-hydroxy-3 , 4-propylenedioxythiophene or hydroxy ProDOT) (20 %) . Optimisation of the process for the synthesis of this mixture may change the ratio of the 2 constituents from 70:30 to 95:5. In some of the further derivatised systems, the hydroxy ProDOT may even disappear after the purification of the raw mixture because of its greater solubility. Both hydroxy groups of the dioxine and of the dioxepine are almost readily reactive, the former more than the latter being a primary alcohol .

Carbamates are easily prepared by reacting the hy- droxymethyl EDOT/hydroxy ProDOT mixture with the appropriate isocyanate in anhydrous toluene. Reflux is

needed for a long time (80-120 hrs) depending on the chain length and further functionalisation of the isocyanate.

Esters are analogously obtained from the starting mixture of alcohols and the proper acyl chloride in the presence of 4-dimethylaminopyridine in anhydrous acetonitrile . Reflux is usually needed (4-6 hrs) .

Ethers are obtained by reacting alkyl- or alkylene halides with alkaline alkoxides of the hydroxymethyl EDOT/hydroxy ProDOT mixture in turn prepared by reacting the hydroxy derivatives with the proper metal hydride in anhydrous acetonitrile. Reflux is needed to complete the reaction.

Very often purification is performed by dry flash chromatography. All final products have been characterised by UV-Vis, IR, ¹ H and ¹³ C NMR and elemental analysis.

Details on film formation

The in-situ chemical oxidative polymerisation is per- formed at low temperatures to prepare electrochromic polymer films on transparent conductive substrates. Principally, the formulation of the coating sols is as follows. First a moderator base (any nitrogen base containing primary or secondary amino functions, also silylated species such as aminoalkyl alkoxy silanes) is dissolved in an appropriate organic solvent (n- butanol, ethanol, 2-propanol) . Second, siIyI functional monomer [from (b) ] is added to the mixture. Optionally, non- silylated monomers prepared according to step a) may be added in order to obtain co-polymers. The mixture is then cooled in a thermostat.

Third, the chosen organosilicon compound (s) and an oxidant are subsequently added to the mixture (in this order) . Within a time window of 20 min after the addition of the oxidant, the coating solution is ap- plied to the substrate and spun-off by means of a spin-coater. After thermal or IR treatment (optionally light curing when light-curable organosilicon compounds are employed) , the polymer films are rinsed in an appropriate organic solvent to remove the overamount of oxidant and dried.

Electrochromic hybrid polymer materials result that are superior to state-of-the-art materials in terms of their bleached state transparency, electrochromic contrast, flexibility, durability and adhesion performance .

Surprising observations and unique characteristics

It was surprisingly found that some of the monomers generated in Step (a) , in particular those bearing long alkyl chains (> 10 C-atoms) could not be elec- tropolymerised whereas they underwent in- situ chemi- cal polymerisation to afford homogeneous, thin films with an extraordinary transparency still maintaining a quite good electrochromic contrast and high cycling stability. This unique characteristic was attributed to the effect of substituent side chains that, when too long, create hindrance to order in the growing conductive chain.

Another remarkably positive feature of the present invention was the time necessary to induce the colour change upon oxidation and reduction, which was in the range of 1-2 seconds.

Another remarkable feature of the present invention is the mechanical integrity and higher stability of the films during potential cycling, being superior to that of the corresponding, purely organic films.

Moreover, it was surprisingly found that by the presence of bi- or tridentate amines such as triethylene diamine or 2-aminoethyl (3-aminopropyl) triethoxysilane the polymerisation rate of the thiophene monomers can be slowed down due to the strong reduction of the oxidizing power of the oxidant (possibly by forming chelate complexes) , thus enabling proper control of the process which is of outmost importance for at- taining coatings on large sized substrates with high optical quality and uniform thickness.

Generally speaking, the polymerisation process should be performed at very low temperatures (preferably at -17 ⁰ C or lower) . However, by the use of amines capable of forming chelate bonds as moderator bases (e.g. silanes derived from ethylene diamine or triamine) , it becomes possible to work at temperatures around 0 ⁰ C, or even higher, which is considered to be another benefit of the invention.

Examples

Preparation was performed at the reflux temperature of the chosen solvent (anhydrous toluene for the carbamates, dry dichloromethane for the esters and anhydrous acetonitrile for the ethers) .

To obtain the allyl carbamate derivative, equimolar amounts of allyl isocyanate (5 % in excess) was added

to the solution of SE, then the mixture was heated at reflux for 80 hours. After the evaporation of the solvent the product was purified by dry flash chroma ^¬ tography.

To obtain the undecanoyl ester derivative, equimolar amounts of 4-dimethylaminopyridine and of the undecanoyl chloride were dropwise added to the solution of SE, and then the solution was heated at reflux for 4 hours, cooled and poured into diethyl ether and filtered to eliminate the pyridinium salt. The sol ^¬ vent was then evaporated under reduced pressure and the pure product was obtained by dry flash chromatog ^¬ raphy.

To obtain the allyl ether derivative, a solution of SE was dropwise added and under nitrogen atmosphere to a suspension of sodium hydride, the mixture was stirred for 3 hours at room temperature to obtain the alkoxy anions. Then allyl bromide was added to the suspension and the mixture heated at reflux till completion of the reaction. The suspension was then diluted with dichloromethane, filtered to eliminate the inorganic salt to give a solution that was evaporated under reduced pressure.

Step (a)

Synthesis of SE-ECIl (the SE undecenoyl ester)

H S 8 ^* 2 yield 72%

10-Undecenoyl chloride (5.9 g, 29 mmol) in dry di- chloromethane was slowly added to a solution of 5 g (29 mmol) of SE dissolved in 40 ml of the same sol- vent containing 4-dimethylamino-pyridine (3.5 g,

29 mmol) . The mixture was heated at reflux for 4 h, cooled, then poured into diethyl ether and filtered to eliminate the pyridinium salt. The solvent was then evaporated under reduced pressure to obtain a yellow oil. The pure product was obtained by dry flash chromatography (SiO ₂ - CH ₂ C1 ₂ /Hexane 4:1). Yield 72 %. The product was characterised by ¹ H-NMR, UV-Vis and IR spectroscopy.

¹ H-NMR δ (CDCl ₃ ): 6.50 (s, 2H), 6.39-6.33 (m, 8H),

5.86-5.76 (m, 5H), 5.24 (quint, J=4.32 Hz, IH), 4.97 (d, J=17.10 Hz, 5H), 4.93 (d, J=IO-Il Hz, 5H), 4.41- 4.18 (m, 20H), 4.07-4.00 (m, 4H), 2.41-2.33 (m, 10H), 2.08-2.00 (m, 10H), 1.70-1.59 (m, 10H), 1.44-1.22 (m, 50H) .

UV-Vis (n-hexane) : λ _max = 236, 256 nm.

IR (%T) : 3115.44 cm ^"1 weak, 3074.94 cm ^"1 weak, 2926.45 cm ^"1 intense, 2854.13 cm ^"1 intense, 1742.37 cm ^"1 intense (C=O) , 1640.16 cm ^"1 weak, 1582.31 cm ^"1 weak,

1484.92 cm ^"1 intense, 1376.93 cm ^"1 intense, 1185.04 cm ^"1 intense, 1025.94 cm ^"1 intense, 912.17 cm ^"1 medium, 759.81 cm ^"1 medium.

Synthesis of SE-CC3 (the SE allyl carbamate)

_α1

Allyl isocyanate (4.1 g, 48.8 mmol , 5 % excess) was added to a solution of SE (8 g, 48.8 mmol) dissolved in 35 ml of anhydrous toluene. The mixture was heated at reflux for 46 h, then added of further allyl isocyanate (0.8 g, 9.2 mmol, reaching the 25 % in excess) and heated again at reflux for 37 h, cooled, and the solvent was evaporated under reduced pres- sure. The product was purified by two dry flash chromatographies: the first (SiO ₂ - CH ₂ Cl ₂ /Et ₂ 0 7:3), the second (SiO ₂ - CH ₂ C1 ₂ /Hexane 8:1) to give a colourless very viscous oil. Yield 78 %. The product was characterized by ¹ H-NMR, UV-Vis and IR spectroscopy.

¹ H-NMR δ (CDCl ₃ ): 6.50 (s 2H), 6.37-6.32 (m, 8H), 5.88-5.79 (m 5H), 5.20 (d J=17.28 Hz 5H), 5.14 (d, J=IO, 48 Hz 5H), 5.10 (s IH), 4.98 (s broad 4H), 4.81 (s broad IH), 4.41-4.18 (m 20H), 4.07-3.98 (m, 4H), 3.86-3.77 (m, 10H) .

UV-Vis (n-hexane) : λ _max =236,256 nm.

IR (%T) : 3341.07 cm ^"1 intense (NH) , 3112.55 cm ^"1 medi- urn, 2921.63 cm ^"1 medium, 1711.51 cm ^"1 intense (C=O),

1644.98 cm ^"1 medium, 1526.38 cm ^"1 intense, 1376.93 cm ^"1

intense, 1247.72 cm ^"1 intense, 1187.04 cm ^'1 intense, 1024.02 cm ^"1 intense, 920.84 cm ^"1 intense, 763.67 cm ^"1 intense .

Step (b)

In a flask 0.34 g (1 mmol) of the functional al- kylenedioxythiophene monomer mixture SE-ECIl (consisting of approx. 80 mol% and 20 mol% of the hy- droxymethyl EDOT and hydroxy ProDOT derivatives, respectively) and 0.20 g (1 mmol) 3-mercaptopropyl trimethoxysilane (MPTMO) were thoroughly mixed. In order to start the hydrolysis of MPTMO, 0.027 g of H ₂ O (1.5 mmol) were slowly added to the mixture. Af- ter the hydrolysis was complete, the mixture was transferred into an aluminium vessel and irradiated by means of a UV curing device at a conveyor belt speed of 0.6 m/min (output power of 6.7 J/cm ² ) . The completion of the thiol-ene coupling reaction was checked by Raman spectroscopy. The reaction can alternatively be carried out without the addition of water.

Step (c)

A mixture of the non-alkoxysilyl functionalised monomer mixture SE-ECIl (1.28 g, 9 mmol) and 3-amino- propyl triethoxysilane (0.22 g, 1 mmol) was added to the above reaction product of step (b) and thoroughly mixed. In a second flask 2.5 mmol of a moderator base was dissolved in 3.71 g (50 mmol) of n-butanol. The moderator solution was stirred for 5 minutes before it was added to the monomer mixture. A solution of Fe (IιI)p-toluene sulphonate (9.97 g, 17.5 mmol) in n- butanol (79.8 g) , pre-cooled in an ice-salt bad, was added to the above mixture and thoroughly stirred

while the temperature was maintained below 0 ⁰ C. After a 5 minutes mixing period, the flask was put in a thermostat and cooled to -17 ⁰ C. The coating was performed by means of a spin-coater. The coating sol was applied to a substrate equipped with a transparent conductor [e.g. k-glass (Pilkington) or T-MO _x PET-ITO foil (Baekert) ] by means of a syringe or pipette. The sample was then spun subsequently at 600 rpm for 30 seconds and at 1200 rpm for 10 seconds. The coated samples were cured in an oven at 120 ⁰ C for 20 minutes. After curing, the films were rinsed in n- butanol or other appropriate solvents (or mixtures of solvents) in order to remove the overamount of Fe (IιI)p-toluene sulphonate . Finally, the films were dried with pressurised and ionised air.

The resulting electrochromic coatings typically have a coating thickness of 200 nm, show excellent adhesion on transparent conducting oxides (such as ITO) and a contrast > 50 % in the visible range of the electromagnetic spectrum. The switching times for darkening and bleaching are in the range of 1-2 seconds in liquid electrolytes (see Fig. 3) .

The resulting electrochromic coatings typically show high stability upon voltage cycling: Fig. 4 shows the behaviour of the SE-ECIl coating after 1000 cycles.

If Step (c) is carried out using a moderator base able to form chelate complexes (such as triethylene diamine) the in-situ polymerisation can effectively be performed at room temperature. The resulting coating solution is suitably stable to attain homogeneous coatings by means of spin, knife (doctor blade) , dip spray coating and roll-to-roll techniques.

The coatings according to the invention further exhibit the following special features:

• Films contain silicon (some atom percent) be- sides carbon, sulphur, oxygen and traces of iron and nitrogen (detectable e.g. by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy) .

• Aliphatic C=C double bonds can be detected in the films (e.g. by IR or Raman spectroscopy), besides the typical absorption (IR) and emission (Raman) bands of ethylene dioxythiophenes .

• The transparency of the films is above 80 %, the electrochromic contrast above 50 % at the wavelength of maximum absorption.

• The films — when applied to clean ITO-surfaces — cannot be detached by immersion in boiling water.

• The surfaces of the films may show characteristic circular structures (visible in scanning electron micrographs) . These structures may result in a slight haze perceptible with the naked eye under low viewing angles (not perceptible at 90 ° viewing angle) .