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Title:
RECORDING MEDIUM FOR THREE DIMENSION OPERATING MEMORY
Document Type and Number:
WIPO Patent Application WO/2006/037279
Kind Code:
A1
Abstract:
Photochromic compounds consisting essentially of two heterocyclic dithienylfulgimides linking with aromatic or heterocyclic moieties are particularly suitable for optical memories. The preferred heterocyclic photochromic bis-fulgimides consist essentially of 2-thienylfulgimides capable of excitation by ultraviolet light to color and change refractive index. A method of preparation of the these bis-fulgimides was carried out. Photochromic materials, in particular, to photochromic compounds and matrices suitable for use in optical working memory systems, including three dimensional working optical memory systems for computers, multimedia applications and the like, were prepared. In particular, bis- fulgimides incorporated into polycarbonate binder are transformed reversibility from open form into cyclic one by electromagnetic radiation. A 3D optical memory system based on the two wavelengths all solid-state laser is proposed.

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Inventors:
BARACHEVSKY VALERY ALEXANDROVI (RU)
KIYKO VADIM VENIAMINOVICH (RU)
KRAYUSHKIN MICHAIL MIKHAILOVIC (RU)
LYIKSAAR SERGEI IGOREVICH (RU)
OFTISEROV EVGENIY NIKOLAEVICH (RU)
PUANKOV YURII ALEXANDROVICH (RU)
STOYANOVICH FELIX MARKELOVICH (RU)
STROKACH YURII PETROVICH (RU)
VALOVA TATYANA MICHAILOVNA (RU)
Application Number:
PCT/CY2005/000003
Publication Date:
April 13, 2006
Filing Date:
October 04, 2005
Export Citation:
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Assignee:
AKIRAM TRADING LTD (CY)
BARACHEVSKY VALERY ALEXANDROVI (RU)
KIYKO VADIM VENIAMINOVICH (RU)
KRAYUSHKIN MICHAIL MIKHAILOVIC (RU)
LYIKSAAR SERGEI IGOREVICH (RU)
OFTISEROV EVGENIY NIKOLAEVICH (RU)
PUANKOV YURII ALEXANDROVICH (RU)
STOYANOVICH FELIX MARKELOVICH (RU)
STROKACH YURII PETROVICH (RU)
VALOVA TATYANA MICHAILOVNA (RU)
International Classes:
G03C1/73; C07D409/14; C07D413/14; G11B7/244; G11C13/04
Foreign References:
JPH03193761A1991-08-23
EP0900798A11999-03-10
JPS6438063A1989-02-08
DD208689A11984-04-04
EP0420397A11991-04-03
Attorney, Agent or Firm:
Michaelides, Andreas (Limassol, CY 3502, CY)
Download PDF:
Claims:
CLAIMS
1. What is claimed is: A family of molecules suitable for use in an optical memory of the form ##STR I ## .
2. A method of preparation of a family of molecules of the #STR 1 #.
3. Photochromic recording media based on polymer binder and thermal irreversible photochromic compounds differing application of photochromic one compound from bisfulgimide class ##STR1## in following relation: 95.896 7 weight % of said polymer binder and 4,23 ,3 weight % of said bisfulgimide.
4. Photochromic recording media as defined in claim 1, comprising polycarbonate as a polymer binder.
5. Photochromic recording media as defined in claim 1, comprising polystyrene as a polymer binder.
6. Application of the photochromic recording media in 3D optical memory systems.
7. A 3D optical memory system, comprising an active photochromic recording medium capable to exist in a first form A absorbing UV irradiation thereof, said first form being photochemically convertible into a second form B absorbing visible irradiation thereof, said second form exhibiting induced absorption or index refraction upon irradiating thereof by electromagnetic radiation, characterized in that said medium material comprises at least polycarbonate or polystyrene and one bisfulgimide according to ##STR1## .
8. A two wavelengths facility based on the two wavelengths all solidstate laser for 3D writingreadingcleaning.
Description:
RECORDING MEDIUM FOR THREE DIMENSION OPERATING MEMORY

DESCRIPTION

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally concerns fulgimides and photochromism. The present invention particularly concerns a new thermal stable photochromic bis- fulgimides.

The present invention relates to the field of photochromic materials, in particular, to photo- chromic compounds and matrices suitable for use in working optical memory systems, including three dimensional optical memory systems for computers, multimedia applications and the like.

Also the present invention is related to devices of three-dimensional optical memory namely to devices for writing-erasing-reading of information within a 3D optical registering medium. The applied devices may be used in all areas of computation where required is storage of big massive of information with possibility of its multiple re-writing. Also, possible is usage of this device for recording, storage and playing of video- and audio-files.

2. Description of the Prior Art

Photochromic fulgimides as related fulgides, a classes of organic compounds which are capable of reversible light-induced coloration, were developed by several research groups (J.D. Margerum, LJ. Miller. In: Technique of Chemistry. Photochromism. V.III. Ed. G.H. Brown. J.Wiley and Sons. N. Y. 1971. P.557; H.G. Heller. In: Fine Chemical for the Electronic Industry. Ed. P. Bamfield. Royal Soc. Chem. London.1986. P.120; J.Whittall. In:

Photochromism: Molecules and Systems. Amsterdam. 1990. P.467; J.Whittall. In:

Applied Photochromic Polymer Systems. Ed. CB. McArdle. Blackie.Glasgov. 1992.P.80; H.G. Heller et al. Spec. Publ.-R.Soc. Chem. 1993. Vol.125, 156, 1993; Yu.M. Chunaev et al. Chem. Heterocycl. Compounds. N 6, 1, 1992 (Rus.); M.Fan et al. In: Organic Photochromic and Thermochromic Compounds. Eds. J.C. Cranoand RJ. Guglielmetti. 1998. Vol.l. P.141; Y. Yokohama. Chem. Rev. V.100, 1717, 2000.

Photochromic fulgimides exhibit several important physical properties, such as thermal stability of both colorless and colored forms, high photoreaction efficiency, high fatigue resistance to repeated coloration-bleaching cycles and light power. Photochromic fulgimides are promising candidates for many technological applications including use in recording media, particularly in erasable optical memory devices. See M.Fan et al. In: Organic

Photochromic and Thermochromic Compounds. Eds. J.C. Crano and R.J. Guglielmetti. 1998. Vol.l. P.141; Y. Yokoyama. Chem. Rew. V.100, 1717, 2000.

For their utilization as 3D optical memory device materials - where the assessing of information is achieved by the written bits — the colored form of the photochromic material will desirably the photoinduced absorption, fluorescence or refractive index fluoresce when illuminated with light.

Recently, a series of heterocyclic photochromic fulgimides have been synthesized. See Otto B, Ruck-Braun K . Eur.J. Org. Chem. N13, 2409, 2003; Wolak MA, Thomas CJ, Gillespie NB, et al. J. Org. Chem. Vol.68, N2, 319, 2003 ; Liang YC, Dvornikov AS, Rentzepis P.M.Macromolecules. Vol.35, N25, 9377, 2002 ;Matsushima R, Nishiyama M, Doi M J Photochem. Photobiol. A Vol.139, Nl, 63, 2001 ; Liang YC, Dvornikov AS, Rentzepis PM J Mater. Chem. Vol. 10, N 11, 2477, 2000; Liang YC, Dvornikov AS, Rentzepis PM .Tetrahedron Lett. Vol. 40, N 46, 8067, 1999; M.Fan et al. In: Organic Photochromic and Thermochromic Compounds. Eds. J.C. Cranoand RJ. Guglielmetti. 1998. Vol.l. P.141

These heterocyclic photochromic fulgimides are thermally stable, fatigue-resistant and undergo near-quantitative conversion to their colored forms upon exposure to UV light. However, these photochromic fulgimides do not provide high light-sensitivity (M.Fan et al.

In: Organic Photochromic and Therrnochromic Compounds. Eds. J.C.

Cranoand RJ. Guglielmetti. 1998. Vol.l. P.141.

The progenitor of this invitation is N-(4-Phenyl)-2-[l-(2,5-dimethyl-3-tienyl)-ethyliden]-3- isopropylidene]pyrrolidin - 2,5-dione ##STR2##( Ryoka Matsushima, Hiroshi Sakaguchi, J. Photochem. PhotobioL A: Chemistry, Vol.108, 239-245,1997).

The need for improved memory devices, memory media and memory processing for computers has been dramatically demonstrated by the increasing speed and computational power of modern computer with vastly more complex programs to access and store in memory. The major factor which is determinant of the size and price of a computer is the memory.

At present time the actual task in the field of information technologies is making data bases for telecommunication linkage systems, defense, HD movies, telemedicine and other applications.

In this connection the development of optical memory with super high information capacity is underway by the way of changing two-dimension carries by three(3D)-dimensional ones. This memory allows to achieve bit density up to 1 Tbit/cm 3 . As this takes place, the reversible (for working optical memory, Parthinopoulos et al. (Science, Vol. 245. Pages 843-

845, 1989)) and irreversible (for archive optical memory, T. Tanaka et al.(Opt. Commun.Vol.

212, N 1-3, 45, 2003) light-sensitive materials are now required.

This invention relates to making one or two-photon photochromic recording media for 2D or 3D working optical memory possessing bit recording.

At the present three general classes of photochromic recording medium exist, namely amplitude recording medium due to the photoinduced absorption as well as phase and fluorescence recording media which exhibit photoinduced refraction and fluorescence during photochromic transformations, correspondingly. These photochromic transformations may be realized under one or two- photon absorption processes.

Generally, a photochromic material in all these devices changes color when irradiated with UV, visible or infrared irradiation while in the ground state. The light is adsorbed by the

ground state molecule, which then undergoes a photochemical reaction to form the photoinduced form. Preferable, the photoinduced state absorbs light at a different wavelength than the ground state of a molecule. The photoinduced form reverts to the initial form by thermal reversion or by being irradiated with light again, preferably light with a different wavelength than the light used to "read" the photoinduced form.

The photochromic compound is incorporated within a 2D or 3D matrix that is transparent to the activating light. The recording medium then is irradiated, preferable by a laser to photochemically change the light absorption of the photochromic recording medium at a site. The 2D or 3D memory device "reads" the information by irradiating the sites with light at a wavelength for which the photoinduced state has a high absorption, index refraction or fluorescence yield. The information associated with a location can be erased by irradiation thereof with light having wavelength causing reverse photochemical change the photoinduced state B back to the ground state A.

The problem of practical implementation of a concept of creating one- or three-dimensional optical memory based on the above phenomenon of photochromism of organic compounds with photoinduced refraction fluorescence refraction , index or absorption detection faces difficulty in choosing a suitable recording media.

The recording media should combine a multitude of physical-chemical properties simultaneously. Among these properties we can distinguish the most evident and simple ones

-molecules of the active photochromic recording media shall be adequate photochromic i.e. absorption bands of form A and form B shall have bigger extinction coefficients and shall not overlap;

-molecules B shall possess thermal stability;

-quantum yields of direct (A to B) and back (B to A) photoreactions shall be sufficiently high;

-form B of photochromic substance should photoinduced changes of absorption, refraction, fluoresce, etc. for determination recorded optical information;

-forma B of photochromic substance should the low change of the adsorption band during read-out of optical information;

-reversible transformations between forms A and B shall be characterized by high recurrence (more 10 4 cycles without any noticeable changes of optical density at the maximum of the photoinduced absorption bands).

Various optical memory devices have been proposed, including 3D optical memory described by Rentzepis in U.S. Pat. No. 5,268,862, and Rentzepis and Esener in U.S. Pat. No. 5,325,324, herein incorporated by reference, a three dimensional laser disc drive system described by Goldsmith et al. in U.S. Pat. No. 5,113,387, herein incorporated by reference, optical memory system and method described by Lindmayer in U.S. Pat. No. 4,864,536, herein incorporated by reference and optical system. Another three-dimensional optical storage memory system is described by Parthinopoulos et al. (Science, Vol. 245,843,1989), also incorporated herein by reference.

Recording media of the different type for 3D optical memory are predominantly developing in USA (Call/Recall Corporation, Irvine and San Diego Universities of California) and Japan

(Japan Science and Technology Corporation, Kyushu, Osaka, and Shizuoka Universities).A variety of photochromic materials have been suggested for use as recording media in working optical memory systems (V. Barachevsky. Sci.Appl.Photo.vol.38,N 3, 315-324, 1997; Proc.

SPIE, vol. 3402,2-10, 1998; Sci.Appl.Photo,vol. 41, N 3, 473-486, 1999; S. Kawata, Y. Kawata. Chem. Rev. Vol. 100, 1777, 2000; H.Bouas-Laurent, H. Durr. Pure Appl.Chem. Vol.

73, 639, 2001).

J. Malkin et al. suggest the use of spiropyrans as photochromic materials in 3D memory devices (Photochemistry of Molecular Systems for Optical 3D Storage Memory, Research on Chemical Intermediates, Vol. 19, No. 2, pages 159, 1993; U.S. Pat. Nos. 5,936,878).

Barachevsky presented the review on photochromic photochromic quinines (Barachevsky V.A. Photochromic quinones. In: Organic Photochromic and Thermochromic Compounds. Eds. J. Crano and R.Guglielmetti. Plenum. New York. 1998, Vol. I 5 pp. 267-314).Fisher et al. in, herein incorporated by references, describe the synthesis and the use of naphthacenequinones for the reversible optical storage of information (U.S. Pat. Nos. 5,208,354; 5,177,2278 and 5,407,885).

The application of diarylethene-type systems with heterocyclic rings was described in Jap. Pat. Nos 89,954. The synthesis and properties of diarylethenes was reviewed by M. Me (M.Irie. In: Organic Photochromic and Thermochromic Compounds. Eds. J.C. Crano and RJ. Guglielmetti. N. Y. and L., Plenum Press. 1999. V.I. P. 207; Chem. Rev. Vol. 100, 1685, 2000). The different dihetarilethenes were used for making optical memory (T.Tsujioka. Mol.Cryst.Liq.Cryst, Vol. 344, 51, 2000; T. Fukaminato et al. Proc. JPN Acad. Ser. B, Vol. 77, N. 2, 30, 2001; Z. Liang et al. Proc.SPIE, Vol. 4930, 134, 2002; X.Mai et al., Proc. SPIE, Vol. 5060, 270, 2003; HXi et al., Proc. SPIE 5 VoI. 5060, 279, 2003; Y. Yokotama ET AL., J. Am. Chem. Soc, Vol. 125, N 24, 7194, 2003.

At the last time the photocromic fulgides and fulgimides (M.Fan, L. Yu, W.Zhao. In: Organic Photochromic and Thermochromic Compounds. Eds. J.C. Cranoand RJ. Guglielmetti. 1998. V.I. P.141) attractive the important attention with the goal of the development recording media for 3D working optical memory ( Y.C.Liang et al., Res.Chem,Intermed., Vol.24, 905,1998; J.Photochem. Photobiol. A. Vol. 125, 79, 1999; J. Mater. Chem., Vol. 10, 2477, 2000; J.Photochem. Photobiol. A. Vol. 146, 83, 2001; A. Kurita et al., Mol.Cryst.Liq.Cryst, VoI 344, 205, 2000; R. Zelensky et al., Vol. 105, N 2-4, 111, 2003; U. S. Pat. Nos. 6,693,201).

The majority of the recording media for 2D or 3D optical memory uses fluorescent readout of optical information. But the written information may be accessed by the detection of the changes in refractive index ( T. Kardinahl et al. Appl. Phys. A. Vol.61, 23, 1995), IR spectra (M. Seibold et al. Chem.Phys.Lett. Vol.225, 135, 1996), photocurrent (T.Tsujioka et. Al. J.Opt. Soc. Amer. Vol. 19, N 2, 297, 2002), molecule design (E.Murguly et al. Angew. Chem. -Intern.Ed. VoI 40, N 9, 1752, 2001; AJ. Mules et al. Adv.FunctMater. Vol. 12, N 3, 167, 2002; B.Z. Chen, et al. Synth. Metals, Vol. 137, N 1-3, 985, 2003;Y.C. Liang et al. Vol. 223 , N 1-3, 61, 2003).

There are several unsolved problems for application of the developed photochromic organic recording media for 2D or 3D working optical memory.

The one problem associated with the use of the proposed spiropyrans as photochromic substrates in working optical memory devices lies in the fact that their photoinduced form is not thermally stable and is capable to revert to the ground state by itself. To prevent the

undesirable spontaneous reversion to the ground state, the matrix carrying these photochromic materials must be cooled to at least -78 C. and preferably lower temperatures. Necessity in such low temperatures as a precondition for efficient functioning of devices utilizing above materials is associated with difficulties in design and limits the scope of possible applications. Besides that spyropyrans usually lose their photochromic properties after a few read — write - erase cycles.

The main unsolved problem with the use all the developed organic photochromic organic recording media in 2D or 3D memory devices based on fluorescence registration is the non- destructive reading. The readout stability of all known photochromic recording media is not sufficient. This means, that even illumination with weak light used for reading can induce the erasing reaction, which is proportional to the numbers of photons absorbed by the media. Therefore after many readout cycles the memory is destroyed.

The other problem is a low light-sensitivity of the photochromic organic media because of the absence any catalytic process for receiving image and restriction solubility ob the photochromic compounds in the polymer binders. This leads to low concentration of light- sensitive centers and, consequently, to low information capacity of the recording medium and optical memory.

The analog of this invitation is a photochromic materials, in particular, based on photochromic compounds from spiropyran class and polyester as matrix suitable for use in optical memory systems, including three-dimensional optical memory systems for computers, multimedia applications and the like. In particular, nonfmorescent spiropyrane is transformed into fluorescent merocyanine by electromagnetic radiation.

The progenitor of this invitation is a photochromic material, in which N-(4-Phenyl)-3-[l- (2,5-dimethyl-3-thienyl)-ethylidene]-4-isopropylidene]pyrrol idine - 2,5-dione (Ryoka Matsushima, Hiroshi Sakaguchi. J. Photochem. Photobiology. A: Chemistry. Vol. 108, 239, 1997) is used in the polymer binder.

Known is a three-dimensional facility for information writing, erasing and reading [Kawata Y., Nakano M., Lee S-C, Three-dimensional optical data storage using three-dimensional optics. - Optical Engineering, v.40(10), p.2247-2254]. In this paper described are various media (single-photon and two-photon) and versions of facility for writing-erasing-reading

based on principle of confocal microscopy, the writing being accomplished by focusing of "write" wave-length radiation into the being written volume of medium and altering refraction index under action of radiation, the reading being accomplished by detecting areas of altered refraction index upon variation of phase of radiation beam of wavelength other than one of writing radiation. The authors note disadvantages of facilities and media applied. In the case of single-photon media too high is mutual influence of layers, in the case of two-photon media necessary is high energy of recording pulse of laser radiation at its small duration that makes it impossible to miniaturize the laser source. Besides, due to high sensitivity of measurement method with respect to phase disturbances necessary is a medium of very high optical uniformity and optical quality of surface (thickness) of the photopolymer layer.

Known is a facility for information writing-erasing-reading in three-dimensional optical memory (P.M. Rentzepis, Three-dimensional optical memory. - US Pat. N°5268862 of Dec. 7 , 1993) based on a photochromic material, typically spyrobenzopyrane bounded in the three- dimensional matrix of polymer. The material has two stable states - spyropyrane and merocyanine, transition from one form to another is initiated by two-photon absorption at wavelength 532 nm. In this case, irradiation is arranged by two laser beams along two mutually perpendicular axes. In this way, achieved is spatial positioning in three-dimensional volume: conversion of photochromic substance occurs only in spot of beams intersection. The second state of photochromic substance produces fluorescence under action of radiation of wavelength 1064 nm, i.e. irradiating the volume by this radiation makes it possible information readout by scanning of fluorescent locations. Erasing is achievable by heating medium locally or entirely e.g. by radiating thereof by 2.12 μ beam. Disadvantages of this facility are similar to those of previous one. Since the write-process is two-photon type, necessary are radiation sources of high peak power, consequently operating at relatively low frequencies. Necessity of positioning of two mutually perpendicular beams into the three- dimensional volume of medium sets limits of a voxel dimensions by units or tens microns, the possible focusing spot being of sub-micron size. Besides homogeneity and surfaces confining the volume must be of high optical quality, the latter could be relatively easy achieved in the cases of glass or crystal matrices. For polymer, obtaining of similar quality at mass- production is problematic or will result in costs increase.

It should be also noted that all described in literature devices of three-dimensional memory based on photochromic medium feature a common disadvantage related to physical

peculiarities of principles of information storage: as areas with varied absorption index or areas with substance converted unto luminescence state. To secure possible maximum record density these areas should be of minimum dimensions. At present, technology enables to focus light into area with geometrical dimensions 0.5*0.5*0.5, in units of wavelength, however efficiency of recording beam energy transformation into conversion of photochromic dope is less than 100 per cent. A typical value of luminescence quantum yield for long-term stable photochromic substances is about 0.05-0.1 [Yongchao Liang, Alexander S. Dvornikov, Peter M. Rentzepis, A novel non-destructible readout molecular memory. - Optics communication, 223(2003), 61-66.], absorption index at the spectral maximum does not exceed 1-2 cm [Satoshi Kawata, Yoshimasa Kawata, Three-dimensional optical data storage using photochromic materials. - Chem. Rev. 2000, 100, 1777-1788]. This restricts necessary readout signal level at minimum volume of the voxel. Also it should be noted that at readout process based on detection of passed radiation at absorption spectrum maximum in the case of single-photon media, partial erasing of the information bit occurs, therefore used is light of wavelength at wing of absorption band [Satoshi Kawata, Yoshimasa Kawata Three- dimensional optical data storage using photochromic materials. - Chem. Rev. 2000, 100, 1777-1788]. Correspondingly, in practice the volume of a voxel must be increased at factor of tens or even hundreds. In the case of single-photon media, in all above works noted is significant cross-sectional influence of recorded layers. More reasonable for information writing-reading seems to use threshold two-photon media, in the latter writing-erasing occurs only if light intensity achieves some limit. However such media require very high power for information writing-erasing, in practice at present attaining of these values is impossible in miniature devices. Basic obstacle for wide use of single-photon media as registering media of optical storage is erasing of information at reading. Taking into account real luminous fluxes necessary for information reading by detecting medium optical density variations entire erasing occurs in 5-10 reading cycles. Hence to avoid above disadvantages the facility must be based on differing approach to information readout. A method to overcome this disadvantage is to apply method of confocal microscopy [A. Toriumi, J.M. Herrmann, S. Kawata, Nondestructive readout of a three-dimensional photochromic optical memory with a near-infrared differential phase-contrast microscope. - Optics letters, v.22(1997), #8, 555- 557]. This method enables to detect variations of refraction coefficient in the recorded area. However in spite of high sensitivity and possibility of single photon media usage since for detecting is used radiation of wavelength at the very wing of absorbance band i.e. not initiating transition of the medium from one state to another this method is not free of

disadvantages at all. The basic disadvantage is namely high sensitivity since detected are not only phase non-uniformities of recordings but also any optical non-uniformities of the disk including variations of thickness about half of wavelength of reading light. In practice this excludes industrial applicability of this method since it requires disks manufactured with "optical" accuracy that makes their production economically unreasonable.

Known is facility for information writing-erasing-reading in optical volumetric memory most close to the being applied one and adopted as a prototype (Wenpeng Chen, Shekhar Guha et al. Optical volume memory. - US Pat. JN°6045888, Apr. 04 th , 2000). The facility comprises optical medium positioning facility, radiation sources generating at two wavelengths λi, λ 2 , optical beam forming system, facility for positioning optical beam, optical radiation detector. The facility is intended for writing into two-photon medium by means its irradiation by λi beam, the writable component being mixed with signal component comprising medium fluorescent under single-photon absorption only in "recorded" state absorbing reading light quanta of wavelength λ 2 . As a dope may be added a component realizing up-conversion of recording radiation into one with shorter wavelength λi necessary for recording. Recording into medium is accomplished by "paragraphs" by spatial modulation of recording radiation beam. Photosensitive medium comprises a multilayer structure of alternating photosensitive and non-photosensitive layers selection thereof may be performed either by spatial positioning of the storage volume or by adjustment of focal length of read- write head. Here, the non- photosensitive layers may comprise optical wave-guides along which propagated is radiation of "read" wavelength. In this case, selection of read layer is fulfilled by directing the radiation only into the being read layer. Disadvantages of this approach is similar to previous: usage of two-photon medium, and, correspondingly, need of high-power radiation sources. Fluorescence used for readout imposes limitations on voxel dimensions to provide acceptable intensities of signal at the "read" process. Use of wave-guide for selection of read layer though solves problem of "read" beam positioning however propagating along the wave-guide light penetrates through separation boundary for 0.5 wavelength hence the required volume of fluorescent material may be obtained only owing to increase of the voxel transverse dimensions and, correspondingly, decrease of recording density. Besides use of single-photon processes inevitably results in partial erasing in each reading act, to avoid this influence the medium is doped with up-converting the radiation component.

SUMMARY OF THE INVENTION

The present invention contemplates photochromic bis-fulgimides that are characterized by photoinduced absorption and refractive index under irradiation of an appropriate frequency. The photochromic fulgimides of the present invention are particularly suitable for optical memories.

The photochromic bis-fulgimides of the present invention exhibit all the important physical properties of photochromic bis-fulgimides; to wit: thermal stability of both colorless and colored forms, high photoreaction efficiency, high fatigue resistance to their repeated coloration-bleaching cycles and light power. Moreover, they are characterized by high photoinduced absorption and refractive index in one (only) stable form.

In one of its aspects the present invention is embodied in a photochromic chemical consisting essentially of colored heterocyclic bis- fulgimides.

hi another of its aspects the present invention is embodied in heterocyclic photochromic bis~ fulgimides consisting essentially of colored derivatives 1,4 - phenylene-bis{3-[l-(2,5- dimethyl-3-thienyl)ethylidene]-4-isopropylidene}pyrrolidin- 2,5-dione capable of excitation by at least ultraviolet light to absorption and refractive index..

These heterocyclic photochromic fulgimides are preferably synthesized by process of (1) condensation of acetone with diethylsuccinate in fert-butanole at the presence potassium tert- butylate, (2) condensation of 3-acetyl-2,5-dimethyl-thiophene with 3-isopropylidene- diethylsuccinate at the presence of potassium ført-butylate in toluene according to Stobbe reactions and following alkaline hydrolysis of obtained diester, (3) cyclization of 2-[α-(2,5- dimethyl-3-thienyl)ethylidene]-3-isopropyliden-succinic acid into cyclic anhydride (fulgide) at the presence a new cyclising agent diethyl chlorophosphate in dry dimethylformamide, (4) interaction between fulgide and aromatic diamines, (5) cyclization of diamides of 1,1- carbonyldiimidazole in dry tetrahydrofurane.

In yet another of its aspects the present invention is embodied in a family of molecules of the form shown in FIG. 1.

These and other aspects and attributes of the present invention will become increasingly clear upon reference to the following drawings and accompanying specification.

The main object of the present invention is to provide a new and improved photochromic recording media having physical and photo-chemical properties for use of these materials in available 2D or 3D optical memory storage devices based on absorption and refraction reading.

Another object of the present invention is to provide a new and improved photochromic recording media defined by high information capacity and which are thermal stable in use and photochemical stable in reuse (read-write-erase cycles) and in which the reading of the information based on absorption or refraction.

Another object of the present invention is to provide new and improved recording medium having increased light-sensitivity value at room temperature.

Another object of the present invitation is to provide new and improved recording media having increasing of the concentration of the light-sensitive centers in volume of recording media.

In accordance with the present invention the medium material having the above improved properties comprises a light sensitive photochromic polymeric compositions based polycarbonate or polystyrene and one of bis-fulgimides.

Therefore, in accordance with the present invention it was unexpectedly revealed that above polymer compositions based on polycarbonate or polystyrene and photochromic compound from a bis-fulgimide class undergo photochromic reaction accompanied with photoinduced changes of absorption and refraction which makes them suitable for the purposes of a 2D or 3D working optical memory system and that the recording medium based on these components has improved performances in comparison with the known in the art compositions.

Another object of the present invention is facility for information writing-erasing-reading in a

multi-layer registering medium based on the 2 wavelength full solid state diode pumped laser intended to overcome the problem of information erasing in the writing medium at reading.

Technical result of multiplication practically to infinity of optical disk readout cycles is achieved by introduction into the existing facility radiation attenuators for each of two wavelengths and chromatic aberration compensator into beam forming system that secures spatial coincidence of the two beams spots at wavelengths of reading-erasing and writing and control of the beams intensities ratio.

hi accordance with the present invention the formulated problem is to be solved by the applied facility for information writing-erasing-reading in multi-layer optical registering medium comprising facility for positioning optical medium, sources of radiation generating at two wavelengths λ ls λ 2 , optical beam forming system, facility for precision positioning optical beam, optical radiation detector with a peculiarity that it is equipped with two independent electrically controlled attenuators for two wavelengths λ \ , λ 2 , into the beam forming system introduced is chromatic aberration compensator, for writing mode radiation power at λ \ being predetermined maximum and at λ 2 being equal to 0, for erasing mode radiation power at λ 2 being maximum and at λ} being equal to 0, for reading mode ratio of radiation power at λι related to one at λ 2 being within the range 0.2-0.7.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of the synthesized photochromic bis-fulgimides.

FIG.2. shows the structure of mono-fulgimide analog , namely N-(4-Phenyl)-3-[l-(2,5- dimethyl-3-thienyl)-ethylidene]-4-isopropylidene]pyrrolidine - 2,5-dione

FIG. 3 is a diagrammatic view showing the reversible photoisomerization, ultimately generating the cyclic structure B from open form A shown on FIG. 1, undergone by the synthesized bis-fulgimides of the present invention when illuminated with UV and visible light.

FIG.4 us showing the structures of synthesized bis-fulgimides

FIG. 5 is a diagram showing the stepwise process of synthesizing the bis-fulgimides on the present invention.

FIG. 6 is a Table 1 showing the chemical data characterizing the synthesized bis-fulgimides.

FIG. 7 is a Table 2 showing spectral-kinetic characteristics for synthesized bis-fulgimides and mono-fulgimide analog (FIG.2) in toluene.

FIG. 8 is showing the absorption spectra before (1), after UV irradiation (2) for mono- fulgimide (FIG.2) analog of bis-fulgimides in toluene.

FIG. 9 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleaching under visible irradiation (2) for mono-fulgimide analog (FIG.2) in toluene.

FIG. 10 is showing the absorption spectra before (1), after UV irradiation (2) for bis- fulgimide 7c in toluene.

FIG. 11 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleaching under visible irradiation (2) for bis-fulgimide 7c in toluene.

FIG. 12 is showing the absorption spectra before (1), after UV irradiation (2) for bis- fulgimide 7a in toluene.

FIG. 13 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleaching under visible irradiation (2) for bis-fulgimide 7a in toluene

FIG. 14 is showing the absorption spectra before (1), after UV irradiation (2) for bis- fulgimide 7b in toluene.

FIG. 15 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleaching under visible irradiation (2) for bis-fulgimide 7b in toluene

FIG. 16 is showing the absorption spectra before (1), after UV irradiation (2) for bis- fulgimide 7d in toluene.

FIG. 17 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleaching under visible irradiation (2) for bis-fulgimide 7d in toluene.

FIG. 18 shows structural chemical formulae of bis- fulgimides (F2-F5) found as suitable for use in working optical memory systems in accordance with the present invention and mono- fulgimide analog (Fl)for comparative study.

FIG. 19 shows UV- visible spectra of recording media in accordance with the present invention before (1) and after (2) exposure to UV light irradiation for mono-fulgimide analog Fl in polycarbonate.

FIG. 20 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleacing under visible irradiation (2) for mono-fulgimid analog F 1 in polycarbonate.

FIG. 21 is a Table 1 showing spectral-kinetic characteristics for synthesized mono - and bis- fulgimides in polycarbonate.

FIG. 22 shows UV-visible spectra of recording media in accordance with the present invention before (1) and after (2) exposure to UV light irradiation for mono-fulgimide analog Fl in polystyrene.

FIG. 23 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleacing under visible irradiation (2) for mono-fulgimid analog Fl in polystyrene.

FIG. 24 is showing the absorption spectra before (1), after UV irradiation (2) for bis- fulgimide F2 in polycarbonate.

FIG. 25 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleacing under visible irradiation (2) for bis-fulgimide F2 in polycarbonate..

FIG. 26 is showing the absorption spectra before (1), after UV irradiation (2) for bis- fulgimide F3 in polycarbonate.

FIG. 27 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleacing under visible irradiation (2) for bis-fulgimide F3 in polycarbonate.

FIG. 28 is showing the absorption spectra before (1), after UV irradiation (2) for bis- fulgimide F4 in polycarbonate..

FIG. 29 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleacing under visible irradiation (2) for bis-fulgimide F4 in polycarbonate.

FIG. 30 is showing the absorption spectra before (1), after UV irradiation (2) for bis- fulgimide F5 in polycarbonate.

FIG. 31 is showing kinetic curves for photocoloration under UV irradiation (1) and photobleacing under visible irradiation (2) for bis-fulgimide F5 in polycarbonate.

FIG. 32 shows an experimental optical setup for testing of the photochromic recording medium sample.

FIG. 33 a-c. Experimental setup for the diode-pumped Nd:YVO4-laser with forth harmonic generation

FIG. 34: The average power, the pulse energy and the duration versus the repetition frequency.

FIG. 35. Block diagram of recording-erasing-reading facility.

DESCRIPTION OF THE PREFERRED EMBODIMENT

1. Introduction

A new class of thermally stable and fatigue resistant photochromic bis-fulgimide derivatives have been synthesized. The absorption spectra, light-sensitivities, kinetic of the

photochemical reactions (photocoloration, photobleaching, photodegradation) of these bis-fulgimides as compared with a mono-fulgimide analog were measured. The absorption spectra of initial open A and photoinduced cyclic form are acceptable for one- and two- photon excitation. The both forms are thermal irreversible. The light-sensitivity for the synthesized bis-fulgimides is more that for mono-fulgimide analog. Bis-fulgimides are characterized by more effective stability to irreversible photochemical transformations. They provide the high recurrence of the photochromic transformations, which exceeds 10 cycles.

The present specification concerns the synthesis and the photochromic behavior of these 4 bis-fulgimides as compared with the mono-fulgimide analog.. As found by the inventors, the light-sensitivity of synthesized bis-fulgimides exceeds the same value measured for a mono- analog.. Some different species of bis-fulgimides described above were synthesized and unambiguously identified by means of NMR 5 MS-spectra and elementary analysis.

The photochromic bis-fulgimides of the present invention have high reversible photochemical reaction efficiency, high thermal stability when irradiated with visible light.

2. The Synthesis of Photochromic Bis-fulgimides

Bis-fulgimides are derivatives of thienylfulgimides containing two thienylfulgimide fragments linked by the aromatic bridges of different type (FIG.l).

The structure of mono-fulgimide analog (FIG.2) is N-(4-phenyl)-2-[l-(2,5-dimethyl-3- thienyl)-ethylidene]-3-isopropyliden - 2,5-dione (Ryoka Matsushima. J. Photochem. Photobiol. A: Chemistry, Vol.108, 239, 1997).

Photochromic bis-fulgimides form a 4n+2 system (FIG. 3,A). When the open-ring form A (known as colorless form) of these bis-fulgimides is irradiated with UV light, a conrotatory ring-closure reaction occurred according to the Woodward-Hoffman selection rules (FIG. 3,B).

This results in the formation of a cyclized structure (known as colored form or B form) whose absorption spectrum is red shifted to the visible region.

2.1 Preferred Synthesis Process

Photochromic bis-fulgimides 7a-d (FIG.4) are prepared from 3-acetyl-2,5-dimethyl-thiophene by the five-stage synthesis. The subject compounds of the present invention have been synthesized according to the following process (FIG.5).

The preferred process of the present invention for obtaining of 1,4 - phenylene-bis{3-[l-(2,5- dimethyl-3-thienyl)ethyliden]-4-isopropyliden)pyrrolydine - 2,5-dione and its analogs includes (1) condensation of acetone with diethylsuccinate in ført-butanole at the presence potassium tert-butylate, (2) condensation of 3-acetyl-2,5-dimethyl-thiophene with 3- isopropylidene-diethylsuccinate at the presence of potassium fert-butylate in toluene according to Stobbe reactions and following alkaline hydrolysis of obtained diester, (3) cyclization of 2-[α-(2,5-dimethyl-3-thienyl)ethylidene]-3-isopropyliden-su ccinic acid into cyclic anhydride (fulgide) at the presence a new cyclizing agent diethyl chlorophosphate in dry dimethylformamide, (4) interaction between fulgide and aromatic diamines, (5) cyclization of diamides of 1,1-carbonyldiimidazole in dry tetrahydrofuran.

EXAMPLE 1.

The synthesis of 1,4-phenylene-bis {3-[l-(2,5-dimethyl-3-thienyl)ethylene-4-isopropyliden} pyrrolidin-2,5-dione (7c).

Stage 1: Preparation of 3-isopropyliden-diethylsuccinate.

31 g (0,275 M) potassium tert-butylate are dissolved in 300 ml of tert-butanole at heating. To the boiling mixture 19 ml (0.25 M) of dry acetone and 52 ml (0,313 M) diethylsuccinate are added during 1 hour. Mixture refluxed during 2 hours, solvent is evaporated. 200 ml of water was added to a residue and the product extracted by ether. The water layer was separated, acidificated by hydrochloric acid up to acidic reaction and extracted by ether. Ether was

evaporated. The residue was refluxed with 200 ml of ethanol and 1 ml sulfuric acid.

Ethanol was evaporated and . the residue was extracted by 200 ml of dichloromethane. After evaporation of solvent the mobile oil is exposed to the vacuum distillation. The yield of 3- isopropylidene-diethylsuccinate is 29,5 g (56 %). .B.p.=116-121°C/8 mm Hg.

Stage 2: Preparation 2-[α-(2,5-dimethyl-3-thienyl)ethylidene]-3-isopropylidensuc cinic acid.

H g (0.1M) t-BuOK dissolved in 250 ml of dry toluene are placed into a round-bottomed flask supplied by a reflux condenser and dropping funnel. To this suspension 20 g (0.09 M) of diethylisopropylidenesuccinate and 14.4 g (0.09 M) of 3-acetyl-2,5-dimethylthiophene in 50 ml of dry toluene are added by drops during 30 min. The reaction is mixed at room temperature during 8 hours. Then solvent is evaporated until dry. 250 ml of water are added and the product extracted by ether two times by portions of 100 ml. The water layer is separated and acidified by HCl up to acid reaction. The residue is extracted by chloroform three times by portions of 70 ml. The organic layer is separated , dried with CaCl 2 . The solvent is evaporated. The residue dissolved in 100 ml of 10% KOH ethanol solution and hydrolyzed during 7 hours, then solvent is evaporated. To the residue 100 ml of water are added and acidified . Diacid is extracted by chloroform. The organic layer is separated , dried under CaCl 2 and is evaporated. The residue is dark-brown ductile oil. To this substance 200 ml of petroleum ether and 30 ml diethyl ether are added . The precipitated crystals are filtered off , washed by petroleum ether with the use of the Shott filter an dried in the vacuum. 11,98 g (44%) of the white crystals of diacid 5 (m.p. 203-205 0 C) are obtained.

Stage 3: Synthesis of [α-(2,5-dimethyl-3-thienyl)ethylidene]-3-isopropylidenesucc inic anhydride.

11.98 g (0.041 M) diacid 5 are dissolved in 50 ml of dry dichloromethane. To this solution 10,4g (0,06 M) of diethyl chlorophosphate are added in 70 ml of dry DMF by drops The reaction mixture is stirred during 3 hours at room temperature. Then solvent and an excess of the ring forming agent are evaporated by the rotor evaporator. To the residue 20 ml petroleum ether (40-70 0 C) are added. It is staying in the freezer (0-5° C) during 1 hour. The precipitated crystals are filtered with the use of the Shott filter, washed by petroleum ether. 8.72 g (77 %) of the pale yellow crystals of anhydride 6 ( m.p. 155-156° C, according to literature - 155-156 0 C) are received after recrystallization from the mixture of chloroform-petroleum ether (1 : 2).

Stages 4-5: Synthesis l,4-phenylene-bis{2-[α-(2,5-dimethyl-3-thienyl)ethylidene]- 3- isopropylidene} succinimide.

To the solution of 0.2 g (0.0018 M) of 1,4-phenylenediamine in 30 ml of dry benzene 1 g (0.0036 M) of fulgide 6 are added. The reaction mixture is boiled during 20 hours. After refluxing the precipitated crystals of amide (Ig) are filtered out and used without the following additional purification. The separated amide crystals are suspended in 30 ml of dry tetrahydrofuran .and l,l-carbonyldiimidazole(0,005 M) are added. The reaction mixture is stirred during 5 hours at room temperature. The solvent has been evaporated. The residue is the light brown amorphous precipitate. It is purified by column chromatography using silica gel. Eluent is the mixture of hexane-ethylacetate (2:1). After evaporation of solvent 0.43 g (38 %) light red crystals of bis-succinimide , m.p. 258-260 0 C (chloroform- petroleum ether). Mass spectrum, m/z (/ rel, %): 624 (87). Found, % : C-68.91 %, H-5.80 %, S-10.17 %. C 36 H 36 N 2 O 4 S 2 . CaIc, % : C-69.20 %, H-5.81 %, S-10.26 %. Data are present in Table on FIG. 6.

EXAMPLE 2-4

The compounds 7a, 7b, 7d have been synthesized according to the similar scheme. Chemical characteristics are presented in Table 1 on FIG.6

The stages 1-3 described above is a general method for the obtaining of key compound β.This compound has been used in the synthesis of bis-fulgimides 7a, 7b, 7d.

Then to the solution of (0.0018 M) corresponding diamine in 30 ml of dry benzene 1 g (0.0036 M) of fulgide 6 are added. The reaction mixture is boiled during 20-40 hours. After refluxing the precipitated crystals of amide are filtered out and used without the following additional purification. The separated amide crystals are suspended in 30 ml of dry tetrahydrofuran .and l,l-carbonyldiimidazole(0,005 M) are added. The reaction mixture is stirred during 5 hours at room temperature. It is purified by column chromatography using silica gel. Eluent is the mixture of hexane-ethylacetate (2:1). After evaporation of solvent has been obtained corresponding bis-succinimide 7a, 7b, 7d. Data of this compounds are present in Table on FIG. 6.

This process is diagrammatically illustrated in FIG. 4. The synthesized bis-fulgimides of the present invention are all represented in the final step of FIG. 4. At least fore species, called species "7a-7d", are both possible and of interest. The structures of the synthesized compounds present on the FIG.5.

An effective method for the preparation of 2,5-dimethyl-3-acetyl-thiophene by Fridel-Crafts reaction of 2,5-dimethyl-thiopene with acetyl chloride in presence SnCl 4 as catalyst has been reported. See Ya. L. Goldfarb and V. P. Litvinov , Journal General Chemistry. (USSR) 5 V.30, 2719(1960).

Intermediates 2,5-dimethyl-3-acetyl-thiophene and diethyl isopropylidenesuccinate were prepared by the methods described in Alan P.Glase, A.Harris, Harry G. Heller, William

Johncock, Stephen n. Oliver, Peter J. Strydom and John Whittall, J. Chem. Soc.perkin Trans.I, 957 (1985); and C. G. Overberger and C. W. Roberts, J. Am. Chem. Soc, 71, 3618 (1949).

2.2. Basic Photochromism and Spectro-Kinetic Properties of the Bis-fulgimides of the Present Invention.

The synthesized bis-fulgides-7a-7d were, found, when illuminated with UV light, to undergo reversible photoisomerization. A diagrammatic view of this reversible photoisomerization of the present invention is shown in FIG. 3. Photoisomerizable molecular structures "A" and "B" are each shown in FIG. 3. The structure of molecular species B which undergoes cyclically reversible photoisomerization, also called photocylcyclization, is diagrammatically illustrated on FIG. 3.

Initially colorless solutions of species 7a-7d become red under excitation with 350-400 nm light. The open colorless forms A of these compounds are characterized by absorption maxima in the region of 310-335 nm (Table 2 on FIG.7, curves 1 on FIG.8, FIG.10, FIG.12, FIG.14, Fig.16). The colored forms B are characterized by absorption maxima in the spectral range of 522-535 nm (Table 2 on FIG.7, curves 2 on FIG.8, FIG.10, FIG.12, FIG.14, Fig.16). The colored forms B can be reversibly bleached by excitation with .λ.>400 nm visible light.

During the bleaching process only the formation of the forms A were observed, which is the preferred configuration for the cyclization process.

It should be noted that absorption maxima of compounds 7a-7d are the same (530 nm) and are shifted to the long-wave visible region as compared with mono-fulgimide analog.

All synthesized bis-fulgimides are characterized by the similar kinetic curves for photocoloration under UV irradiation (curve 1 on FIG. 9, FIG.11, FIG.13, FIG.15, FIG.17) and photobleaching under visible irradiation (curve 2 on FIG. 9, FIG.ll, FIG.13, FIG.15, FIG.17) from the Hg-lamp possessing power of 250 W. But the light-sensitivity value for all bis-fulgimides is more as compared with mono-fulgimide analog (Table 2 on FIG.7).

All isomeric forms of these bis-fulgimides 7a-7d show excellent long term room temperature thermal stability. No changes were detected, by means of HNMR and UV-VIS absorption spectroscopy, when pure A and B forms were dissolved in toluene and acetonitrile solvents and kept in the dark at room temperature for over a month. This data suggests strongly that no decomposition nor any other thermal reactions take place.

All synthesized compounds are characterized by high recurrence of the photocoloration and photobleaching processes which in excess of 10 4 cycles (Table 2 on FIG. 7)..

3. Preparation Recording Media

In accordance with the present invention samples of photochromic recording media were prepared according to a following procedure.

To a solution of tetrahydrophyrane (10 ml) added the certain quantity of a polymer binder (up to 96,7 weight %) and dissolved at room temperature during 1 day with stirring. To a mixture thus obtained a solution prepared by addition of 4,2-3,3 weight % for one of photochromic mono- and bis-fulgimide (FIG.18) with stirring.

A light sensitive layer of photochromic medium material of 5-30 mu thickness is prepared from the thus obtained solution by method of irrigation of a Teflon cap of 5 cm diameter with subsequent drying on air.

According to FIG.3 the extracted colorless film in the A form is transformed to the B colored form under UV irradiation. This B form may be transformed to the initial A form under visible irradiation (> 400 run). This photochemical reversible transformations are thermal irreversible ones.

Now with reference to non - limiting examples 5-16 and FIGS. 19 - 32 it will be explained how an active medium comprising the above polymers can be prepared and used for recording and reading of information in 3D optical memory devices.

EXAMPLE 5

95,9 mass % of polycarbonate Lexan SD 1318-112 are dissolved in 10 ml of chloform. To this polymer solution added 4,1 mass % of photochromic mono-fulgimide compound F 1. A light- sensitive layer of photochromic recording medium of 20 mu. thickness is prepared from the thus obtained solution by method of irrigation of a Teflon cap of a 5 cm diameter with subsequent drying on air. Then the prepared photochromic film is extracted from the Teflon cap. This film was irradiated at the room temperature with a UV light produced by high pressure Hg-lamp (DRS -120) from the distance of 120 cm through a glass filter. The absorption spectra and before and after UV irradiation (FIG.19) were measured. After this the sample was irradiated by UV and visible light through the silicate glass filters transmitting and cutting UV irradiation. The kinetic curves for photocoloration and photobleaching processes and are recorded (FIG.20). The kinetic of thermal relaxation of UV induced form into an initial form is measured too. The determined maxima absorption band for the B form, the maximum value of the photoinduced optical density characterizing the light-sensitivity of the photochromic recording medium as well recurrency of photochromic transformations are presented in Table 3 (FIG.21) . The colored B form had no any changes of the photoinduced optical density during one month of dark storage. It is seen that the sample are characterized by the acceptable light-sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices.

EXAMPLE 6

According to the procedures described in examples 5, the sample differing a presence of photochromic compound Fl in polystyrene was prepared and measured. The obtained data are presented on the FIG. 22 and 23 as well in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light-sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices.

EXAMPLE 7

According to the procedures described in examples 5, the sample differing a presence of photochromic compound F2 (4,2 weight%) instead of compound Fl was prepared and measured. The obtained data for the photochromic film of 20 mu thickness are presented on the FIG. 24 and 25 as well in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light-sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices. The light-sensitivity of this sample is more as compared with the sample prepared according to the procedures described in examples 1.

EXAMPLE 8

According to the procedures described in examples 7, the sample differing a thickness of 30 mu was prepared and measured. The obtained data for this photochromic film of 30 mu are presented in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light-sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices. The light-sensitivity of this sample is more as compared with the sample prepared according to the procedures described in example 1.

EXAMPLE 9

According to the procedures described in examples 5, the sample differing a presence of photochromic compound F3 (3,3 weight.%) instead of compound Fl was prepared and measured. The obtained data for the photochromic film of 20 mu thickness are presented on

the FIG. 26 and 27 as well as in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light-sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices. The light-sensitivity of this sample is more as compared with the sample prepared according to the procedures described in example 1.

EXAMPLE 10

According to the procedures described in examples 9, the sample differing thickness (5 mu) was prepared and measured. The obtained data for this photochromic film are presented in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light- sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices. This sample is compares with the sample prepared according to the procedures described in examples 1 in light-sensitivity.

EXAMPLE 11

According to the procedures described in examples 5, the sample differing a presence of photochromic compound F4 (3,9 weight.%) instead of compound Fl was prepared and measured. The obtained data for the photochromic film of 20 mu thickness are presented on the FIG. 28 and 29 as well as in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light-sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices. The light-sensitivity of this sample is more as compared with the sample prepared according to the procedures described in example 1.

EXAMPLE 12

According to the procedures described in examples 11, the sample differing a thickness of the photochromic film (5 mu) was prepared and measured. The obtained data for this photochromic film are presented in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light-sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical

memory devices. The light-sensitivity of this sample is more as compared with the samp! prepared according to the procedures described in example 1.

EXAMPLE 13

According to the procedures described in examples 5, the sample differing a presence of photochromic compound F5 (3,6 weight. %) instead of compound Fl was prepared and measured. The obtained data for the photochromic film of 20 mu thickness are presented on the FIG. 30 and 31 as well as in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light-sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices. The light-sensitivity of this sample is more as compared with the sample prepared according to the procedures described in example 1.

EXAMPLE 14

According to the procedures described in examples 13, the sample differing a thickness of the photochromic film (5 mu) was prepared and measured. The obtained data for this photochromic film are presented in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light-sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices. This sample is compared with the sample prepared according to the procedures described in examples 1 in light-sensitivity.

EXAMPLE 15

According to the procedures described in examples 6, the sample differing a presence of photochromic compound F5 (3,5 weight.%) instead of compound Fl was prepared and measured. The obtained data for the photochromic film of 20 mu thickness are presented in Table 3 (FIG.21). It is seen that the sample are characterized by the acceptable light- sensitivity to UV and visible irradiation well-known laser sources, practically unlimited thermal stability and may be used in 2D or 3D optical memory devices. The light-sensitivity

of this sample is more as compared with the sample prepared according to the procedures described in examples 1.

4.Making Optical Systems

Efficient conversion of radiation to the fourth harmonics requires high-quality laser beam and high peak output power. Such pulses can be produced by using Q-switch mode of generation. Both passive and active Q-switching can be used. Passive Q-switched lasers need no switching electronics and possesses reduced size of the system. Nevertheless, if the pumping conditions change, then the repetition frequency and the duration of the pulses may vary in such systems. Passive Q-switch at the output power > 1 W operates at a lower initial light transmission and possesses higher passive losses.

Minimum duration of the pulses have been observed using electro-optical shutters, however, high- voltage triggering pulses are needed in this case and certain technical difficulties exist at high operation frequency.

Acousto-optical shutters possess low passive losses and operate in a wide range of frequencies. The drawbacks caused by a long duration of the switching process can be compensated by a properly chosen geometry of the cavity under longitudinal pumping by laser diodes, high-gain active medium, and a short length of the cavity.

In Fig. 34a, a schematic diagram is shown of Nd:YVO 4 laser with acousto-optical Q- switching for extra-cavity conversion of the radiation to the fourth harmonics. It is known, that the shortest pulse duration and highest peak power are obtained in a quasi-CW laser at the repetition frequency v ~ 1/τ, where τ is the spontaneous lifetime of the gain medium.

For Nd:YVO4 laser we have τ ~ 90μs is, hence our laser system operates at the repetition frequencies 10-2O kHz.

In the repetition-frequency range the duration of the radiation pukes slightly varied from 7 to 8 ns at the half-height.

Thus, at the repetition frequency 12 kHz, the peak output power is ~ 3.6 kW. In Fig. 35, the average power P, the energy E and the duration r of the radiation pulses are presented versus the repetition frequency for Nd:YV04 laser with the acousto-optical Q-switching. The cavity length is about 25 mm. The optimum transmission of the mirror is 25% at the repetition frequency 12 kHz, which corresponds to maximum output power.

Further conversion of the radiation of Nd: YVO 4 laser occurred sequentially in KTP and BBO crystals. The focus lengths of the lenses provide optimum focusing of radiation in nonlinear crystals for obtaining maximum average power of the fourth harmonics radiation. The parameters of the laser system are given in Table 1.

Table 1: Parameters of the laser system

In Fig. 34b, the schematic diagram of Nd: YVO 4 laser is shown where a double-pass scheme is used for nonlinear conversion to both second and fourth harmonics. Here, the spherical (R

= 100 mm or R = 150 mm) dichroic (HR at the primary frequency and AR at the frequency of the harmonics) mirrors were used for focusing laser radiation into nonlinear crystals and the plane dichroic (possessing high reflectivity at the both wavelengths) mirrors for the second pass. In such geometry of the cavity we obtained the efficiency of the conversion to the second harmonics increased by 15-20 %, however, with no increase in the power of the radiation at the wavelength 266 nm. It seems to be connected with the quality of the focusing optics and non-optimal parameters of the latter.

An interesting laser scheme is shown in Fig. 34c, where an intracavity frequency conversion in the crystal KTP is used. It is known that additional elements introduced inside the cavity increase passive losses, which, in turn, makes the laser pulse duration longer.

In our investigations we used nonlinear crystal KTP of the width 1 mm for the intracavity up- conversion. One face of the crystal has coating that is HR at the wavelength λ=532 run and AR at λ= 1064 nm. The other face is HR for λ=1064 nm and AR for λ=532 nm. Thus, the nonlinear crystal operates simultaneously as a reflecting and an output mirror. The small thickness / = 1 mm of the crystal results in low passive losses. The nonlinear element was placed on copper arm that was thermostabilized by means of a controlled Peltier cooler. This stabilization compensates phase shifts and provides phase matching.

The output power of the "green" YVO4 laser with the intracavity frequency conversion and the acousto-optical Q-switching at the frequency 12 kHz increases by a factor of 1.5-2 as compared to the extracavity frequency conversion and reaches 150-230 mW. The pulse duration in this case slightly increases to 10-11 ns. Hence, the peak power is also greater in this case. However, laser operation in this configuration is not stable and requires fine adjustment of the cavity parameters.

The acousto-optical Q-switched diode-pumped Nd:YVO4 laser comprises a Fabri-Perot resonator as it is shown in Fig. 34. Short pulses are produced in this laser due to a compact acousto-optical Q-switch inside the laser cavity with low losses. The pumping diode laser of the type ATC2529 "ATC-Semiconductor Devices, Saint-Petersburg" with the emitting area 500 x 1 μm provides the pumping energy 3 W at the wavelength 808 nm. The pumping beam is first partially collimated by a cylinder lens and then focused into the laser crystal by a three-lens objective. The pumping spot dimensions are 200 X 150 μm. The pump diode is mounted on a thermoelectric cooler and is kept at the optimum temperature in order to match the absorption band of the laser crystal. Approximately 80% of the diode-laser output energy is collected and hits the input mirror of the cavity.

The a-cut, 1%-Nd doped 1-mm long Nd:YVO4 crystal was coated for high reflection (HR) at 1064 nm and high transmission (HT) at 808 nm from the input side. The other face has antireflection (AR) coating at the wavelength 1064 nm. The crystal is mounted on a copper holder. The 1-cm long fused silica Q-switcher has AR coatings at the wavelength of the fundamental frequency on both faces and is driven by RF 5-W generator at the central frequency 80 MHz. The mirror of the active element and the flat output coupler form a short cavity of the length 25 mm. The optimum value was determined 75%.

The radiation of the Nd: YVO4 laser was first up-converted to 532 nm. Intracavity (Fig.

34c) and extracavity configurations of the frequency doubling were studied (Figs, 34a and 34b).We have obtained the frequency doubling for 1, 5, 7, and 13-mm long, type II KTP (KTiOPO 4 ) crystals. The long crystals (/ = 5, 7, 13 mm) have AR coatings on both faces at the fundamental and second-harmonics wavelengths. The short crystal (I = I mm) has one face with HR coating at 532 nm and AR coating at 1064 nm. The other face of the crystal has HR coating at 1064 nm and AR coating at 532 nm. The latter crystal was used for intracavity frequency doubling.

The UV (266 nm) radiation is generated at the second stage. In the stage of intractivity FHG we used a 6-mm long BBO crystal (the type I phase matching) with AR coatings at the wavelengths of the second ant the fourth harmonics.

Facility for information writing-recording-reading in multilayer optical registering medium (Fig.35) comprises radiation source (1) generating at two wavelengths λi, λ 2 (solid state laser on Nd: YVO 4 crystal with radiation conversion into second and fourth harmonics, laser generates at λi=0,266μ, λ 2 =0,532 μ), dichroic Y-joints (2,4,5), optical beam forming system (6), optical beam positioning unit (8), optical medium positioning unit (9), optical radiation detector (10). The entire facility features two independent electrically controlled attenuators (3) of beams λi, λ 2 , beam forming system (6) includes chromatic aberration compensator (7). The facility operates as follows: radiation of laser (1) enters into a dichroic Y-joint (20) embodied on basis of optical fiber Y-joints or of dichroic mirrors. The joint has 2 outputs, at each present is radiation of only ether λ \ or λ 2 . Then radiation from each of outputs enters two-channel electrically controlled attenuator (3) realized as ether fiber or integrated optics device. The attenuator secures independent modulation of radiation at each of wavelengths. Then beams of λi, λ 2 via mixer (4) similar to joint (2) but inversely attached, and via joint (5) is fed (e.g. via optical fiber) onto input of wide aperture beam forming system (focusing system) (6) which secures focusing of beams of λi, λ 2 . Into the optical system (6) introduced is a chromatic aberration compensator which provides matched optical propagation paths at both working wavelengths. Mounting of system (6) enables positioning of beam (8) with respect to multilayer optical medium (8) what ensures beam re-focusing along depth of the medium. Facility for medium positioning

Medium positioning facility (9) secures assignment of writing-erasing-reading layer and coordinates targeting of point of writing-erasing-reading in the layer plane. Operation mode

(writing, erasing or reading) is chosen by radiation intensity of corresponding wavelength control by attenuators (3). The attenuators are controlled as follows: at writing mode radiation power at λ \ is maximum, at λ 2 is 0 (zero); at erasing mode radiation power at is 0 and at λ 2 is maximun, for reading mode ratio of radiation power at related to one at λ 2 being within the range 0.2-0.7. Reading of written information takes place by registration of reflected from optical medium signal passing through the dichroic joint (5) to the optical radiation detector (10).

EXAMPLE 16

The sample from Example 5 was studied with the goal of the development possibilities for 3D multi-layer readable and rewritable systems based on the new generation of the photochromic materials and the UV full solid-state laser with frequency conversion. The investigation was carried out with this photochromic sample and a two length-wave UV-laser system as above with output power 40 mW at λ=532nm and 3 mW at 266 nm. The experimental setup is presented at the FIG.32. After photopolymer's exposing by 266nm radiation its absorption coefficient for 532nm radiation will have to increase. The ratio of average power values of the reading signal (532nm) related to the recording signal will have to be less than 0,01. Because by influence of the reading signal with power comparable with power of the writing signal the useful information will be erase. In the experimental investigation demonstrated was that the absorption coefficient for λ=532nm (reading) exhibits linear growth of 15-30% with energy exposition at 266 nm (recording radiation) within the range 9 to 18 mJ/mm 2 at λ=266nm. After exposing the recorded spot by laser irradiation of λ=532nm and energy comparable to recording exposition (λ=266nm) the absorption coefficient was recovered to initial value (erasing process). The obtained results shows that this photochromic material enables to develop the new generation of the 3D optical storage disks. Application of a full solid-state laser with radiation frequency conversion to second and fourth harmonics is preferable. Application of this photopolymer and a full solid-state laser may increase recording density of the DVD size for 2-4 times. The number of layers in the recordable media may increase up to 4-6 since reflection layers between informational those are not necessary. The present photochromic material makes it available read/write speed about 1 Mb/sec.

5. Experimental Results

A and B forms of bis-fulgimides obtained by scheme shown in FIG. 4 were obtained directly by condensation of the 2-[l-(2,5-dimethyl-3-thienyl)ethylidene]-3-isopropylidenesuc cinic anhydride with corresponding diamines followed by column chromatography purification and then recrystallization. The colored forms (B-form) of these bis-fulgimides were prepared by irradiating, with 360 ran light, the A-form bis-fulgimides in toluene or acetonitrile solution. The structure and purity of the compounds obtained were ascertained by NMR, MS and elementary analysis. All the solvents were HPLC grade or spectral grade and were used without further purification.

AU spectra and kinetic curves were measured in 1 cm 3 quartz cells at room temperature. The UV-VIS absorption spectra were recorded on a Gary 50 spectrophotometer.

Photoirradiation of the photochromic solutions was carried out using a 250 W Hg arc lamp (DRSH-250, Russia). Light of the appropriate wavelength was selected by either a monochromator or a cut off optical filter. A mini magnetic stirring bar was used to mix the solution.

All spectra and kinetic curves of the prepared photochromic films were measured at room temperature. The UV-VIS absorption spectra were recorded on a Cary 50 spectrophotometer.

Photoirradiation of photochromic films was carried out using a 250 W Hg arc lamp (DRSH- 250 ,Russia). Light of the appropriate wavelength was selected by cut off glass optical filters UFS-2 and ZS- 12 (Russian samples) transmitting UV and visible (>400 urn) light for photocoloration and photobleaching, correspondingly

The investigation was carried out with a photochromic sample and a two length-wave UV- laser system as above with output power 40 mW @ λ=532nm and 3 mW @ 266 ran. The experimental setup is presented at the fig.32.

After photopolymer's exposing by 266nm radiation its absorption coefficient for 532nm radiation will have to increase. The ratio of average power values of the reading signal (532nm) related to the recording signal will have to be less than 0,01. Because by influence of

the reading signal with power comparable with power of the writing signal the useful information will be erase.

In the experimental investigation was demonstrated that the absorption coefficient for λ=532nm (reading) exhibits linear growth of 15-30% with energy exposition at 266 nm (recording radiation) within the range 9 to 18 mJ/mm 2 @ λ=266nm. After exposing the recorded spot by laser irradiation of λ=532nm and energy comparable to recording exposition (λ=266nm) the absorption coefficient was recovered to initial value (erasing process).

In the experimental investigation was demonstrated that reading the information without it erasing with using of the mixture of the two beam (λ=532nm and λ=266nm) is possible.

6. Conclusion

A new class of thermally stable photochromic bis-fulgimide derivatives have been synthesized.

Therefore the, present invention will be recognized to be embodied in a photochromic chemical consisting essentially of colored heterocyclic bis-fulgimides, and in a method of preparation of such heterocyclic bis-fulgimides.

These heterocyclic photochromic bis-fulgimides are synthesized by process of (1) condensation of acetone with diethylsuccinate in fert-butanole at the presence potassium tert- butylate; followed by (2) condensation of 3-acetyl-2,5-dimethyl-thiophene with 3- isopropylidene-diethylsuccinate at the presence of potassium tert -butylate in toluene according to Stobbe reactions and following alcaline hydrolysis of obtained diester, (3) cyclization of 2-[α-(2,5-dimethyl-3-thienyl)ethylidene]-3-isopropyliden-su ccinic acid into cyclic anhydride (fulgide) at the presence a new cyclising agent diethyl chlorophosphate in dry dimethylfomamide, (4) interaction between fulgide and aromatic diamines, (5) cyclization of diamides of 1 , 1 -carbonyldiimidazole in dry tetrahydrofuran. This produces a family of molecules of the form shown in FIG. 4.

The absorption for an initial open form A and a photoinduced cyclic form B as well as kinetic curves for photochemical reactions of coloration and bleaching of these bis-fulgimides were

measured. The experiments of the inventors suggest that synthesized bis-fulgimides demand to requirements for preparation of recording media surpass and surpass the mono- fulgimide analog on the light-sensitivity value to UV irradiation. The spectral characteristics, kinetic ..stability of A B forms of these bis-fulgimides as function of temperature and coloration/bleaching reversible cycles are acceptable for above mention application.

In accordance with the preceding explanation, variations and adaptations of the processes and materials in accordance with the present invention will suggest themselves to a practitioner of the chemical arts.

In accordance with these and other possible variations and adaptations of the present invention, the scope of the invention should be determined in accordance with the following claims, only, and not solely in accordance with that embodiment within which the invention has been taught.

A new class of thermally stable photochromic recording media based on bis-fulgimide derivatives and polymer binders namely polycarbonate Or polysterene have been synthesized. The absorption for an initian open form A and a photoinduced cyclic form B as well as kinetic curves for photochemical reactions of coloration and bleaching of these recording media were measured. The experiments of the inventors suggest that synthesized photochromic recording media based on new bis-fulgimides demand to requirements for preparation of recording media and surpass the mono-fylgimide analog on the light-sensitivity value to UV irradiation.

The spectral characteristics, kinetic ,stability of A B forms of developed recording media as function of temperature and coloration/bleaching reversible cycles are acceptable for above mention application namely in 2D and 3D working optical memory. The possibility of realization of these devis was supported by making experimental set-up.

It can be readily appreciated that reading of the information recorded in accordance with the presesnt invention can be easily carried out by a well developed, computerized, fast and commercially available CCD device.

In conclusion it should be pointed out that recording and reading of information based on elaborated photochromic recording media based on polycarbonate or polystyrene and two wavelengths facility based on the full solid state laser as well as one of bis-fulgimides of the present invention has the following advantages:

1. For recording of information it is sufficient to use only very low power, even a CW light sources.

2. The layer within the film can be illuminated from all four sides thereof, thus allowing to reach the required pump beam power density.

3. For reading of recorded information it is sufficient to use the well developed and available methods and equipment.

4. For reading of recorded information it is possible to use the mixture beam with two wavelengths (λ=266nm and 532) to provide reading information without erasing one.

It should be understood that the present invention should not be limited to the above described examples and embodiments.

Changes and modifications can be made by one ordinarily skilled in the art without deviation from the scope of the invention.

The scope of the present invention is defined in the appended claims. However it should be understood that the features disclosed in the foregoing description, in the following claims and/or accompanying examples and/or tables and/or figures may separately and in any combination thereof be material for realizing the present invention in diverse forms thereof.

Main goal of the experiments was the investigation of the development possibilities for 3D readable and rewritable systems based on the new generation of the photochromic materials and the UV full solid-state laser with frequency conversion.