FR2774998A1 - Photochromic material undergoing stable light-induced variation in refractive index and/or birefringence useful in optical data recording and reading systems, ophthalmic lenses, etc. - Google Patents

Abstract

Photochromic material capable of undergoing a stable light-induced variation in refractive index and/or birefringence outside the absorption bands of the photochromic material comprises optically anisotropic photochromic molecules optionally covalently bonded to a solid matrix. An Independent claim is also included for a photochromic material capable of undergoing a stable light-induced variation in refractive index and/or birefringence in the infrared, comprising optically anisotropic photochromic molecules optionally covalently bonded to a solid matrix.

Description

PHOTOCHROMIC MATERIAL WITH STABLE VARIATION
REFRACTION INDEX AND / OR BIRÉFRINGENCE
The invention relates to materials having refractive index and / or birefringence variations related to photochromic properties. Recall only that organic photochromism is the transition between two isomers A and B showing a marked difference in their absorption or emission spectrum, induced by an electromagnetic field. In general, the colorless form A is photocolored by absorption of a UV photon. The decolorization of the molecule B, that is to say the reaction back to A, is by absorption of a photon in the visible. This photochemical process is most often in competition with the thermal discoloration corresponding to the return to the thermodynamically more stable form A. However, some photochromic molecules, for example in the family of dithienylethenes or fulgides, exhibit thermally irreversible photochromism.

The photochemically reversible transformation of photochromic systems is generally accompanied by a polarizability variation. These photochromic molecules therefore have the capacity to change the refractive index of the medium in which they are located and this sufficiently far from their absorption band. For example,
The photochemical behavior of several molecules of the 1,2-dithienylethene family, dispersed in transparent polymethyl methacrylate (PMMA) films, was studied by Yoshida et al. (Journal of Photochemistry and Photobiology A:
Chemistry (1996) 265-70). Reversible changes in refractive index (up to 10-3) have been observed in the infrared.

 The organic photochromic materials may be in the form of molecular layers obtained either by vacuum evaporation of "active" molecules or by dispersion of molecules in a polymer matrix and deposition by centrifugation.

 The object of the invention is to obtain photochromic materials which have significant variations in refractive index and / or birefringence, while having a high durability, and which are preferably easy to implement.

 The subject of the invention is a material schematized in FIG. 1, consisting solely of photochromic molecules (1) or else comprising an organic, or mineral, or organo-mineral matrix and photochromic molecules at least partially bound to the solid by a ( 2) or several covalent bonds (3). The material then has a photochromism, with a photochemically reversible and thermally irreversible transformation, which is associated with a significant variation in refractive index outside the absorption bands of the material, preferably greater than 10-3.

The present invention relates to photochromic molecules with thermally irreversible transformation, especially fulgides and / or preferably 1,2-dithienylethene type molecules bearing various substituents X, Y, R, R ', of general formula:

where X, Y may be reactive functions (typically -OH, -COCI, -CHCH2, ...) possibly allowing covalent grafting to a solid matrix;
R are hydrocarbon groups which may contain heteroatoms, typically R = CH3, C6H13;
R 'is a cyclic group or not, typically R' = (-CF2CF2CF2-).

The major interest of the invention lies in:
- On the one hand in the choice of photochromic molecules: by choosing it with reactive functions, we can control the nature of the bond between the molecules and a solid matrix, by choosing it with a photochemically reversible and thermally irreversible transformation, we can obtain very stable index variations outside the absorption bands; by choosing it with strong linear absorption dichroism (high anisotropy), stable birefringence variations can be induced in polarized light.
on the other hand, in the choice of the molecule-matrix bond when using a solid matrix: by covalently choosing it, the concentration of molecules can be increased by eliminating the phase separation problems observed in the case of simply dispersed molecules. in a polymer and thus exalt the refractive index changes. In addition, these strong interactions immobilize the molecules in the matrix which makes it possible to stabilize a birefringence induced by the polarized light.

 Preferably, the matrix according to the invention is obtained by organic or inorganic polymerization (sol-gel). A very advantageous aspect of the polymerization is that it makes it possible to develop matrices in very varied forms, solid material, layer, or even fibers. In particular, it is therefore possible to obtain the photochromic material according to the invention in the form of a layer whose characteristics, in particular thickness, can be controlled. The photochromic material may therefore be in the form of a thin layer, preferably having a thickness of between 10 nm and 50 μm. A second advantage in the context of the invention is that the monomeric precursors can be functionalized by different organic compound groups.

 According to the invention, at least a portion of the photochromic active compounds are grafted onto the matrix. In the context of the invention, the grafting can take two forms the first is to make the matrix and then functionalize by grafting the photochromic molecules to appropriate active sites, in particular located at least on the surface of the matrix. The second is to make the matrix from molecular precursors carrying photochromic active compounds, having one or more chemical bonds therewith. This grafting is carried out by a polymerization of at least one precursor which has been previously functionalized by these active compounds, directly or via a group or compound of organic type which is "passive" vis-à-vis the property of photochromism but which facilitates the bond between the precursor and the active compound, it is thus possible to obtain, preferably, a material in the form of an organic network, mineral or hybrid, modified by organic grafts. The meaning of the invention is very advantageous for various reasons: on the one hand, it makes it possible to increase the level of active compounds in the matrix as much as possible, by using only functionalized precursors. reasons, to combine functionalized precursors non-functionalized precursors, or at least "passive" vis-à-vis the photochromism On the other hand, the grafting reduces the mobility of the components ac to stabilize anisotropy.

 The grafting of molecules is well known in the case of organic polymers: the molecule is either a pendant group (single covalent bond) or a group incorporated into the polymer chain (two covalent bonds). Many organic polymers can be used for the material of the invention such as poly (methylmethacrylate), poly (ethylmethacrylate), polystyrene, polyamides, polycarbonates, polyesters, polyimides, etc.

When the matrix is obtained by polymerization of the sol-gel type, it is carried out in particular from at least one organo-mineral precursor of the organosilicon or organometallic type such as an alkoxide. In fact, the sol-gel process is based on liquid phase inorganic polymerization reactions, which usually take place in three stages: a precursor or a mixture of precursors is hydrolysed; the polycondensation of these hydrolysed species, generally at room temperature, leads to the formation of a relatively porous and amorphous solid. A low temperature heat treatment then makes it possible to densify the material. The precursors which most interest the invention are silicon alkoxides of the Si (OR) n type (with R organic radicals), functionalizable by different organic groups (R ') which are active or passive for photochromism, for example to obtain formulas of the type
R'Si (OR) 3. The material according to the invention can then be considered to be constituted, for example, by a mineral or hybrid network of the siliceous backbone type, that is to say a polymer network that can combine covalent bonds of Si-O-Si type. and links
Si-C. It is also possible to envisage: the partial presence of mineral networks of the metal oxide type such as networks based on titanium oxide, zirconium or niobium obtained by hydrolysis of precursors of the M (OR) n type, with OR a group alkoxy and M a metal of the type Ti, Zr, Nb; the partial presence of passive hybrid networks obtained by hydrolysis of precursors of the R'-Si (OR) 3 or R'R "-Si (OR) 2 type with R 'and R" of the organic alkoxy groups OR, methyl, phenyl, vinyl.

 The matrix may also be obtained by copolymerization of at least one organo-mineral precursor of organo-silicon type and at least one organic-type monomer carrying a photochromic active compound. The organic monomer may be, for example, saturated or unsaturated ester type such as C (CH 2) (CH 3) (COOE), E symbolizing the active compound. The matrix is obtained from an organomineral copolymer which is crosslinked by the sol-gel process.

 According to a variant of the invention, the material consists solely of molecular layers obtained either by evaporation under vacuum or by centrifugation of a solution of molecules.

 Potential applications of organic photochromes are important and varied, particularly in the fields of variable optical transmission materials ("organic glasses" photochromic) components for guided optics and optical storage of information.

 The principle of "all optical" systems proposed for recording and reading information is generally based on variations in absorbance or rotational power in the visible (see Tsujioka et al US patent 5316900 - 1994). The disadvantage of these systems is that the reading of information is accompanied by the principle of its erasure.

 A small number of works concern systems where the reading is performed in the field of infra-red transparency.

 A first example (Toriumi et al. Optics Letters 22, 8, 1997, 555) consists in detecting in the IR a small difference in refractive index between two photochromic isomers of the spiropyran type. However, the thermal reversibility between the two isomers limits the information storage time to a few hours.

 Another proposed route in the case of azobenzenes by Rochon et al. (Chemistry of Materials 1993, 5, pp. 403-411) is to induce optical anisotropy by "trans-cis-trans" photoisomerization. The absorption of polarized light in the absorption band of the transoid form induces "trans-cis" isomerization with a probability proportional to 20, where (3 is the angle between the dipole moment of the transoid molecule and the direction The shape "cis" is thermodynamically unstable at room temperature, isomerizes in "trans" with modification of its orientation.The photoisomerization cycle continues until saturation of the anisotropy where the Dipole moments of the molecules are perpendicular to the polarization of the pump lumen.As a result, the material becomes dichroic in the absorption band and birefringent out of this band.The reading is then performed in the infra-red transparency band by measurement. photoinduced birefringence.

The major disadvantage of this system is that when the pump beam is cut, the material generally returns to the isotropic state with relaxation kinetics that depends on the mobility of the molecules in the solid matrix.

 - The use of a photochromic material described in the invention, having a significant variation in refractive index outside the absorption bands (preferably in the infra-red and possibly in the visible), photochemically reversible and thermally irreversible makes it possible to propose an information writing stable over time (subject to protecting the visible light material) and a reading channel outside the absorption band, and therefore not disturbing for the information previously recorded. In addition, each photochromic molecule individually exhibits strong anisotropy and, accordingly, a high value of linear absorption dichroism. The material of the invention is initially optically isotropic because of the random orientation of the molecules.

However, the decolorization by linearly polarized light breaks the isotropy: the molecules "oriented" along the axis of polarization of the light are preferentially discolored. As a result, the material itself becomes dichroic in the absorption band and birefringent out of this band. The writing - reading method is then as follows:
initialisation of the medium by UV photo-coloration,
write information by selective bleaching in linearly polarized light in the visible absorption band,
reading in the transparency band, preferably infra-red, by measuring the polarization variation resulting from the photoinduced birefringence,
erasure by UV photo-staining.

Another use of the material of the invention relates to planar guides. The planar guide is the basic element of the "integrated" approach. This element is constituted by a substrate on which is manufactured the guide which allows to connect together the different active components such as sources, modulators-demodulators. At the level of the passive components, there are, in addition to optical linear guides, all kinds of patterns such as couplers ensuring the communication or the distribution of information between several channels, and more complex components such as interferometers of the type
Mickelson and Mach Zehnder.

 The photochromic properties of the material of the invention deposited in film can be used to inscribe in the layer guides limited in both dimensions.

Irradiation by a pump beam is performed through a mask. Photochemical transformation occurs in exposed areas whereas in non-irradiated areas, molecules remain in their original form. We obtain an alternation of zones whose refractive indices are very different. A diffraction grating may also be inscribed by projecting onto the film an interference pattern produced by the mixing of two coherent light beams having the same linear polarization states. Cross-polarization networks can also be written by the same technique inside the film. It is therefore possible to shape confined guides, phase and polarization networks, couplers, Bragg mirrors and all kinds of patterns by illuminating the layer through the corresponding masks.

 The active layer may find use in optical ophthalmic devices, particularly in diffractive networks.

 Another application consists in using the material of the invention for obtaining photochromic ophthalmic lenses. The said material may, in particular, be deposited on the surface of the lens in the form of a layer or incorporated in the mass of the lens.

 Finally, an application of the material of the invention concerns the production of optical articles comprising a utility refractive index gradient inscribed in said material.

By utilitarian refractive index gradient is meant a gradient index fulfilling an optical function usable in the desired application. In particular, the gradient may be intended to impart additional optical power to an ophthalmic lens (whether this power is positive or negative).

 The gradient may still have the object of correcting optical aberrations in a spectacle lens. Another ophthalmic application consists in producing ophthalmic lenses with progressive power, in particular contact lenses.

Other advantageous details and characteristics emerge below from non-limiting embodiments, with reference to the appended figures which represent:
Figure 1: Schematic of the material of the invention consists of either only photochromic molecules (1) or a solid polymeric matrix with photochromic molecules grafted as a pendant group (2), or incorporated into the polymer chain (3).

Figure 2: The chemical formulas of typical photochromic active molecules
3: the chemical formulas of sol-gel precursors and organic polymerization monomers not functionalized with photochromic molecules
Figure 4: The chemical formulas of sol-gel precursors and organic polymerization monomers functionalized with photochromic molecules
FIG. 5: A synthetic scheme of a sol-gel precursor functionalized by a photochromic material
FIG. 6: A graph showing by UV-visible spectroscopy the photochromic behavior of a layer according to the invention obtained from the functionalized precursor of FIG. 5
FIG. 7: A diagram illustrating photodecoloration experiments, in linearly polarized visible light, of a photochromic layer according to the invention, obtained from the functionalized precursor of FIG. 5.

Figure 8: A series of three graphs showing the characterization of the decolorization kinetics in polarized light with the evolution of transmission (1), absorption dichroism (2) and birefringence (3) as a function of time. 'exposure.

FIG. 9: Various photographs showing the realization on a layer according to the invention, obtained from the functionalized precursor of FIG. 5, of "all-optical" reversible devices such as diffraction gratings (1), couplers (2 and 3) or a Mach-Zehnder interferometer.

The manufacture of the material of the invention and its use will be described according to the following steps
A - selection of photochromic molecules
B - Selection of organosilicon precursors and organic polymerization monomers not functionalized with photochromic molecules
C-grafting of photochromic active compounds to organo-silicon precursors and / or to organic polymerization monomers
D - selection of the mode of formation of an active layer
E - operation of the active layer as a recording medium
F - "all-optical" reversible devices such as diffraction gratings or waveguides.

 Step A of selection of the photochromic molecules conditions the photochromic properties of the material. Chemical formulas of typical molecules are shown in Figure 2. They carry reactive functions and belong to the family of 1,2-dithienylethenes and fulgides, molecules whose photochemical transformation is thermally irreversible.

Step B for the selection of organosilicon precursors and organic polymerization monomers determines the nature and property of the solid matrix obtained by polymerization. Rigid matrix precursors, such as sol-gel matrix and vitreous high temperature polymers, which will reduce molecular motions, will preferably be used. The chemical formulas are indicated in FIG. 3. The sol-gel precursors are, for example, methyltriethoxysilane, designated under the abbreviation
MTEOS, triethoxysilane, designated by the abbreviation HTEOS, 3-aminopropyltriethoxysilane, designated by the abbreviation APTEOS, 3-isocyanatopropyl-triethoxysilane, designated by the abbreviation ICPTEOS. The organic polymerization monomers are, for example, methacryloyl chloride, designated by the abbreviation CMA, 4-chloromethylstyrene, designated by the abbreviation CMS.

 Step C consists in covalently attaching a photochromic molecule selected in step A to at least one of the precursors selected in step B to obtain a functionalized precursor for the polymerization. The functionalized precursors are represented in FIG. 4: HTEOS is functionalizable by fulgide, ICPTEOS and CMA by dithienylethene 1, apteos or CMS by dithienylethene 2.

* ICPTEOS functionalized with dithienylethene 1, designated in Figure 2, is synthesized according to the scheme of Figure 5, under the following conditions:
105.3 mg (0.19 mmol) of dithienylethene 1 (1,2Bis- [5 '- (4 "-hydroxyphenyl) -2'-methylthien-3'-yl] perfluorocyclopentene), 53.7 μl (0.38 mmol) mmol) of triethylamine and 146 μl (0.57 mmol) of 3-isocyanatopropyltriethoxysilane (ICPTEOS) are dissolved in 3.5 ml of anhydrous tetrahydrofuran This solution is stirred under nitrogen at 72 ° C. for 7 hours. The solution is cooled to room temperature and then the tetrahydrofuran and triethylamine are evaporated on a rotary evaporator, The mixture thus obtained is purified by recrystallization from hexane to give 161.6 mg (0.15 mmol, yield: 81%) functionalized precursor, designated FIG. 5 under the abbreviation DTE 1 Si and bearing two triethoxysilane groups, in the form of a pale blue powder.

DTE lSi is characterized by nuclear magnetic resonance (NMR) proton (1H) and carbon (1 3C), UV / visible absorption and infra-red spectrometry (IR). Wall. N. H (200 MHz, CDCl 3): δ = 0.69 (m, 4H: -CH 2 -Si), 1.25 (t, 18H: CH 3 -CH 2 -O-
Si), 1.72 (m, 4H: -CH 2 -CH 2 -CH 2), 1.94 (s, 6H: methylthienyl), 3.28 (m, 4H: NH
CH2-), 3.84 (q, 12H: CH3-CH2-O-Si), 5.32 and 4.88 (t, 2H: NH-CH2- and conformer), 7.14 (d, 4H phenyl) , 7.21 (s, 2H: thienyl), 7.51 (d, 4H: phenyl). NMR 13C (50
MHz, CDCl3): 6 = 8.2 (-CH2-Si), 15.2 (methylthienyl), 19.0 (CH-CH2-O-Si), 23.7 (
CH2-CH2-CH2), 44.2 (NH-CH2-), 59.3 (CH3-CH2-O-Si).

UV / Visible Absorption x (i 104 l.mol-1.cm-1): colorless DTElSi, 290 nm (3.5). Colored dTlSi, 315 nm (2.6), 381 nm (1.1), 587 nm (1.6). is the molar extinction coefficient.

 I.R. (CCl 4) 1752 cm -1 (carbamate).

 Step D consists in producing the material, preferably in the form of a thin layer.

 The first matrix is obtained by sol-gel polymerization of the precursor functionalized with a dithienylethene, designated in FIG. 4a, under the following conditions: 81.8 mb (0.078 mmol) of DTE I Si are dissolved in 1 ml of tetrahydrofuran. 0.156 ml (0.78 mmol) of methyltriethoxysilane (MTEOS) is added to the solution before adding 59 μl of acidic water at pH = 1. After stirring for one hour, 59 μl of pyridine are added to neutralize the medium and initiate the condensation of the silanol siloxanes. The soil thus prepared is filtered ave. a 0.45 μm porosity filter.

 The soil is then deposited on a substrate and then spread by centrifugation (spin coating technique). The film obtained is condensed by heating at 70 ° C. for 15 hours The substrate can be a glass slide, a metallized glass slide, a crystalline silicon slide or any other transparent substrate The thickness of the film varies from a few nanometers to a few microns depending on the dilution of the soil and the centrifugation rate For example, a 0.65 μm thick photochromic film was obtained by deposition of undiluted soil by centrifugation at a speed of 3000 rpm. The photochromism of this layer is characterized by the UV / visible absorption spectra in the "colored" and "discolored" states, and the refractive indices at 785 nm, measured by the attenuated total reflection method. a layer deposited on a glass slide covered with a layer of gold, are respectively 1.533 for the discolored film and 1.573 for the colored film.

  The second layer is made solely from dithienylethene 3 molecules, designated in FIG. 2, under the following conditions: The dithienylethene 3 is solubilized in tetrahydrofuran at a level of 1.64 * 10 -2 mol / l. A drop of this solution is deposited on a substrate of polycarbonate or crystalline silicon that was previously removed from its oxide layer by washing with hydrofluoric acid. By centrifugation at a speed of 1000 rpm a film of 60 nm thickness is obtained. This amorphous molecular film is photochromic. The refractive indices before and after staining were measured by phase modulation ellipsometry. The refractive indices of the film at 800 and 1300 nm are respectively 1.62 and 1.61 before staining and 1.78 and 1.71 after staining, ie changes in refractive index from 0.16 to 800 nm and 0.10 to 1300 nm.

 Step E consists, by polarized light illumination, in generating and characterizing an optical anisotropy in the photochromic film of the invention made in step D, showing its operation as an all-optical recording medium.

For example, photodecolorization experiments in linearly polarized visible light were performed on a 85 nm thick sol-gel photochromic film deposited on a glass substrate and whose production was described in the example of FIG. 'step
D. The experimental setup is shown schematically in Figure 7. The sample is initially stained by exposure to unpolarized UV radiation (Ro = 318 nm) located in the absorption band of the unstained form of the photochromic molecules. Then, it is illuminated at near-normal incidence (= 15) by the linearly polarized intensity beam F1 (polarizer PI perpendicular to the plane of incidence: TE polarization) of a gas laser.
HeNe of wavelength (hi = 633 nm) located in the visible absorption band of the colored form of photochromic molecules.

 Over time, the molecules that absorb light hl are discolored. This discoloration causes a change in the absorption coefficient of the material which is accompanied by a variation of its refractive index outside the absorption bands (for example in the infra-red for a light of wavelength X2 = 785 nm). Since the optical properties of an individual molecule are highly anisotropic, the characteristic fading time of each molecule depends on the orientation of its anisotropy axis with respect to the direction of the electric field of light. Thus, over time, the initially isotropic material becomes anisotropic and then, within very long exposure times, the anisotropy disappears. This anisotropy introduces two optical effects: a linear dichroism at hl (and Bo) and a linear birefringence at k2.

 Figure 8 shows the characterization of the decolorization kinetics in polarized light. Three quantities are measured as a function of the exposure time: the transmission at X1 (graph 1), the absorption dichroism at X1 (graph 2) and the birefringence at B2 (graph 3).

 - The transmission 111 (t) / I (t = oo) (1) is measured on the detector D1. The theoretical curve (dotted line) perfectly reproduces the variation of the experimental signal. Two physical quantities are used as adjustable parameters: the volume concentration of the material in photochromic molecules and a characteristic time X of decolorization of a molecule. The characteristic time T depends on the incident intensity, the probability of absorption of a photon by a molecule and the quantum yield of discoloration. According to the measurement of the absorption coefficient of a solution of molecule in known concentration, one deduces simply, on the one hand, the volume concentration d at very long times I '(oo) is drawn on the graph 2. This quantity is measured via a synchronous detection amplifier. The maximum value of dichroism is reached quickly and is worth 5% for a layer only 85 nm thick. Note that, on average, during this experiment, the sample receives at B1 an intensity whose polarization is perpendicular to the axis of anisotropy at only 0.25% of the intensity Ij used to decolorize. the characteristic decolorization times in this direction are 400 times longer: the parasitic discoloration induced by the probe beam of the dichroism thus affects only very little its measurement and only at very long times.In the experiments presented here this disturbance does not reach than 10% at the end of kinetics.

 - For the measurement of the birefringence the separating plate L and the neutral filter are removed while the analyzer is introduced. The sample is illuminated at normal incidence by the beam F2 of intensity I2 of a laser diode of wavelength X2. The polarization of this light is modulated between the circular right and circular left modes by the modulator M. At the crossing of the sample, the birefringence induced by the simultaneous discoloration in polarized light of wavelength B1 introduces a different ellipticity for the two modes of polarization. This modulation of the ellipticity is transformed, by a linear analyzer oriented at 45C with respect to the axis of fading, into a modulation AI2 of the intensity collected on the detector D2. The variation as a function of time of normalized A12 on the incident intensity I2 is plotted on graph 3. This quantity rapidly reaches a maximum of 1%. Taking into account the values of the physical quantities of the system previously determined, the theoretical curve (dotted line) gives access to the value of the optical anisotropy of the molecule (defined as the difference between the anisotropic part and the isotropic part of the probability of absorption of a molecule relative to the sum of these two quantities): A = 98.5%. Note that the photoinduced birefringence is persistent as long as the sample is not illuminated in its absorption bands and even if it is illuminated outside these absorption bands (for example under illumination at B2 with densities of power of the order of 1 RW., um-2 for several hours no decrease in the birefringence signal could be detected).

 From these results, it is possible to extract the characteristics of the system for high density information writing / reading applications. Under the conditions of the experiment described here, a power density (at the wavelength λ1) of 40 mW is required. > m-2 to write binary information to I MHz.

To read the information at 10 MHz with a signal-to-noise ratio of 10, a power density (at the wavelength k2) of 2.5 uW.um-2 is required. These characteristics can be considerably improved by methods of optimizing the medium, for example by simply depositing the thin layer of the photochromic material on a reflective layer and working in reflection geometry. It should be noted that the performance of this material relating to applications for storing and reading high density information is conferred by obtaining essential properties
a very high anisotropy of the individual molecules: A = 98.5%,
a high volume concentration of the material in active molecules: C = 5.5 mol.l -1, inducing a high absorption rate and a large index difference outside the absorption bands between the colored and uncolored states of the material,
- the thermal irreversibility of the photochemical reaction,
the orientation stability of the molecules bound to the matrix by covalent bonds.

 Step F consists of producing, from the layer produced in step D, reversible "all-optical" devices such as diffraction gratings or waveguides. Some of these devices are represented in FIG. 9: diffraction gratings (1), the Y part (2) and the central part (3) of a coupler (3), the detail of a Mach-Zehnder interferometer (4). They were made on colored films by illumination with a UV lamp at 312 nm, by masking, then visible exposure by a tungsten lamp. Diffraction efficiency measurements carried out on the 10 μm (1) grating confirmed an index variation of 4.10.2 between the two states of the photochromic layer prepared according to the technique described in the first example of step D .

Claims (24)

 1. A photochromic material in which a stable variation can be induced by the light, that is to say remanent in the absence of illumination in the absorption bands of said photochromic material, refractive index and / or birefringence outside the absorption bands of said photochromic material, characterized in that it consists of a solid matrix and optically anisotropic photochromic molecules at least partially linked to the solid by a covalent bond, or consisting solely of photochromic molecules.  2. Photochromic material in which a stable variation can be induced by light, that is to say remanent in the absence of illumination in the absorption bands of said photochromic material, refractive index and / or birefringence in the infra-red, characterized in that it consists of a solid matrix and optically anisotropic photochromic molecules at least partially linked to the solid by covalent bond, or solely consisting of photochromic molecules.  3. The material of claim 1 wherein the stable variation of refractive index is induced in visible light.  4. Material according to any one of claims 1 to 3 characterized in that the molecules have a thermally irreversible photochromism, in particular selected from the series of dithienyl ethenes and / or fulgides.  5. Material according to any preceding claim wherein the index variation is greater than 10-3.  6. Material according to any one of the preceding claims, characterized in that all or part of the photochromic molecules are grafted as a pendant group on the solid matrix.  7. Material according to any one of the preceding claims, characterized in that all or part of the photochromic molecules are grafted by several covalent bonds to the solid matrix.  8. Material according to any one of the preceding claims, characterized in that the matrix is obtained by organic polymerization.  9. Material according to any one of the preceding claims, characterized in that the matrix is obtained by polymerization of at least one organic monomer carrying a photochromic molecule.  10. Material according to any one of the preceding claims, characterized in that the solid matrix is obtained by sol-gel polymerization of at least one organomineral precursor, in particular organo-silicon such as an alkoxide.  11. Material according to any one of the preceding claims, characterized in that the solid matrix is obtained by sol-gel polymerization of at least one organo-mineral precursor carrying a photochromic molecule.  12. Material according to any one of the preceding claims, characterized in that the solid matrix is obtained by copolymerization of at least one organomineral precursor of the organosilicon type and of an organic monomer, at least one carrying a photochromic molecule.  13. Material according to any one of the preceding claims, characterized in that it is in the form of a thin layer with a thickness of 10 nm to 50 μm.  14. "All optical" system for recording and reading information comprising at least one layer of the material according to any one of the preceding claims and operating on the following principle: e initialization of the medium by UV photo-coloration of the material, e writing information by selective bleaching linearly polarized light in the visible absorption band, e read in the infra-red transparency band by measuring the polarization variation resulting from photoinduced birefringence, erasing by UV photooloration.  15. "All optical" system for recording and reading information according to claim 14 characterized in that it is disposed on a transparent rigid substrate.  16. The "all optical" information recording and reading system according to claim 14 or 15 for which a reflective metal layer is deposited on the material according to any one of claims 1 to 13 and for which the measurements according to Claim 14 are made in reflection geometry.  17. Reversible "all-optical" devices such as diffraction gratings or waveguides (possibly birefringent) made by masking then insolation UV / visible light polarized or not, comprising at least one layer of the material according to any one of claims 1 to 13.  18. Ophthalmic optic devices, in particular in diffractive gratings comprising at least one layer of the material according to any one of claims 1 to 13.  19. An optical article comprising a utility refractive index gradient inscribed in a material as defined in any one of claims 1 to 13.  20. Photochromic ophthalmic lens characterized in that it comprises a photochromic material according to any one of claims 1 to 13.  21. Ophthalmic lens according to claim 20 characterized in that said photochromic material is incorporated in the mass of the lens.  22. Ophthalmic lens according to claim 20, characterized in that said photochromic material is present in the form of a layer deposited on the surface of the lens.  23. Article or ophthalmic lens according to one of claims 19 to 22, characterized in that this article or this lens is a spectacle lens.  24. Article or ophthalmic lens according to one of claims 19 to 22, characterized in that this article or this lens is a contact lens.