Photorefractive properties

V. PHOTOREFRACTIVE PROPERTIES OF MOLECULAR MATERIALS BASED ON METHINE DYES... 

The electron transporting 9-(dicyanovinyl)thioxanthene moiety and electrooptically active vinylaniline units have been combined in the succinate esters 601. The compounds exhibit good photorefractive properties with high optical quality <2003SM(139)11>. 

Linkage isomerizations have also been observed for other small molecules such as N2, N02, NCS, S02, and dimethylsulfoxide (DMSO).15 The isomers are likely participants as intermediates in biorelevant ligand interchange or addition processes, in the NO recombination after photolysis, or even in the route to NO release from the ES in aqueous, room-temperature photochemistry (Section 7.7). Indeed, the photo-switchable nitrosyl compounds are an attractive class of materials with favorable photochromic and photorefractive properties, potentially useful for optical and biomedical applications. 

Finally, a class of compounds which is gaining attention because of their photorefractive properties is the sillenites, Bii2MO20 (M = Si, Ge, other metal ions). They can be prepared by a variety of methods but, for several derivatives, the most satisfactory route is a hydrothermal one. Thus, single crystals of these compounds may soon be prepared for commercial purposes [110]. 

The investigation, which focused on the use of various chain transfer agents, utilized A -vinylindole, 2-methyl-A-vinylindole and 3-methyl-A-vinylin-dole to synthesize polymers with controlled molecular weights and low poly-dispersities. The photorefractive properties of these polymers were then further investigated. 

Therefore, good photorefractive properties can be seen only for materials that combine good charge generation, good charge transport, or photoconductivity, and good electro-optical activity. 

NLO properties are provided by including chromophore compounds, such as an azo-t)q)e dye, which can absorb photon radiation. The chromophore may also provide adequate charge generation. Alternatively, a sensitizer may be added to provide or boost the mobile charge required for photorefractive properties. 

These composites exhibit very low glass transition temperature, despite the absence of a plasticizer. The materials show excellent photorefractive properties. 

G. B. Jung, T. Mutai, R. Fujimura, S. Ashihara, T. Shimura, K. Araki, and K. Kuroda. Temperature dependence of photorefractive properties of PVK-... 

J. Ortiz, F. Femandez-Lazaro, A. Sastre-Santos, J. A. Quintana, J. M. Vil-lalviUa, P. Boj, M. A. A. Diaz-Garcia, J. A. Rivera, S. E. Stepleton, C. T. Cox, andL. Echegoyen. Synthesis and electrochemical and photorefractive properties of new trinitrofluorenone-C-60 photosensitizers. Chem. Mater, 16(24) 5021-5026, November 2004. 

This polymer contains an electro-optic chromophore (labeled as EO), a chargetransporting group (labeled as CT) and an alkyl group to control the Tg of the polymer (labeled as CTG). The relative ratio of these groups can be varied to optimize the photorefractive property (5). 

The material has to simultaneously possess photoconductivity and electro-optical effect to have photorefractive properties. Typical candidate materials have low glass transition temperature, frequently reduced by the plasticizer. Diffraction efficiency is improved by addition of the plasticizer because chromophore groups have higher rotational mobility and increase their contribution of birefringence to the total refractive index modulation. ... 

Jung GB, Mutai T, Fujimura R, Ashihara S, Shimura T, Araki K, et al. Temperature dependence of photorefractive properties of PVK-based composites. J Appl Phys Part 1 2004 43(12) 8316-21. 

Wright D, Gubler U, Moemer WE, DeClue MS, Siegel JS. Photorefractive properties of poly(siloxane)-triarylamine-based composites for high-speed applications. J Phys Chem B 2003 107(20) 4732-7. 

On the other hand, formation of photorefi active silicone composite with good performance was reported A carbazole-substituted polysiloxane that was sensitized by 2,4,7-trinitro-9-fluorenone was used as a photoconducting medium and l-[4-(2-nilrovinyl)phenylpiperidine was added as an optically nonlinear chromophore. The photorefractive property of polymer was determined by diffraction efficiency using a 100 pm-thick film. The maximum diffraction efficiency (rj max) of 71% was obtained at the electric field of 70 V/pm. 

Several heteroaromatic ring structures have also been incorporated into poly(arylene vinylene) structures using the same soluble-precursor polymer methods used for PPV. Poly(thienylene vinylene) (179) and poly(furylene vinylene) (180) have been prepared. Metalloporphyrins have also been incorporated into poly(arylene vinylene)s (175) to investigate photorefractive properties. Aromatic poly(azomethines) have also been prepared from a solution condensation of an aromatic diamine with aromatic dialdehydes (181), but these materials are less conjugated than their PPV counterparts. Various copolymers of phenylene vinylenes with phenylene, thienylene, and furylene moieties have also been studied (182). 

Neurgaonkar R.R., Cory W.K., Oliver J.R., Ewbank M.D., Hall W.F. Development and modification of photorefractive properties in the tungsten bronze family crystals. Opt. Engng 1987 26 392-405... 

Dissymmetric systems shows exciton splitting of dichroic absorptions and optical activity and photochromic materials having NLO, photoresponsiveness and photorefractivity properties, which occurred due to the presence of azoaromatic and chiral functionalities in the polymers [62]. Finally, novel optically active multifunctional methacrylic copolymers were synthesized, which contained side-chains chiral moieties and linked to a photoconductive carbazolic and to a photochromic azoaromatic chromophores... 

Gasperson, ).D., Smith, B., Glazer, E., and Moerner, W.E. (1999) Photorefractive properties of poly(N-vinyl carbazole) based composites for high speed applications. Chem. Mater., 11, 1784-1791. 

The present studies are mainly devoted to silicon carbide (SiC)-based materials in the form of isolated clusters, nanopartides, or several architectures, which exhibit various original features. The interests in SiC is motivated by the large offered possibihties from structural aspects as well as physical responses such as electronic, optics, photovoltaic or dielectric properties. Additionally, beyond good thermal stability and mechanical hardness, the SiC is versatile from structural aspect (more than 170 polytypes), electronic behavior (a variable energy gap from 2.4 to 3.3 eV) as well as photorefractive properties (Vonsovici et al. 2000). As matter of fact, the nanocrystalline size modulates all the intrinsic parameters involved in the parent bulk materials. When nanopartides are associated with suitable matrixes, promising new potentialities... 

Applications of these materials are oriented toward the development of hybrid photochromic films for waveguides [87], high refraction index for LED encapsulation [283], or materials showing holographic as well as photorefractive properties [284]. 

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