Photochromic hybrid materials

Therefore, the chemical linking of the dye molecules is only worthwhile if it results in a substantially better performance of the resulting materials. For the reasons discussed below, this is mainly expected for nonlinear optics (NLO) dyes. However, other dye-containing materials were also prepared by this approach. For example, new transparent photochromic hybrid materials were prepared by sol-gel processing of Si(OEt)4, sUanol-terminated dimethylsiloxane oligomers and triethoxysilylpropyl-substituted spirobenzopyranes, and fluorescent glasses and films from pyrene derivatives covalently tethered to RS103/2 (R = alkyl, phenyl) . 

Biteau, J., Chaput, F., Lahlil, K., Boilot, J.P., Tsivgoulis, G.M., Lehn, J.M., Darracq, B., Marois, C., and Levy, Y. (1998) Large and stable refractive index change in photochromic hybrid materials. Chem. Mater, 10,... 

He, T., Yao, J. (2006). Photochromism in composite and hybrid materials based on transition-metal oxides and polyoxometalates. Progress in Materials Science, 51, 810-879. http //dx.doi.Org/10.1016/j.pmatsci.2005.12.001. 

Less attention has been paid to the thermochromic properties [72-77] of these hybrid materials, although they can be used as temperature sensors [78-82]. Some photochromic compounds such as naphthopyrans and spirooxazines show thermochromic properties, being the naphthopyrans, better photochromic but worse thermochromic compounds than spirooxazines. Inorganic thermochromic compounds such as those based on copper and tungsten embedded in sol-gel matrices are being widely studied as temperature sensors. 

Photochromic Inorganic and Organic-Inorganic Hybrid Materials... 

Photochromic organic-inorganic hybrid materials are one of the most studied systems. It is believed that the synergy of organic and inorganic compounds in hybrid materials can preserve or even improve the features of the components. Nowadays, it has been demonstrated that hybrid systems can also confer the material new properties, different from those of the single components [6,10]. 

The change of color of the photochromic materials upon irradiation with UV light can be used as a UV radiation sensor [125-130] or temperature sensor [131-133], optical memory devices and switches [134-138], and optoelectronic applications [139,140]. Photochromic hybrid coating having a remarkable long-term stability of both the colored and colorless states in the dark (bistability) was reported [141]. 

Pardo, R Zayat, M., and Levy, D. (2011) Photochromic organic-inorganic hybrid materials. Chem. Soc. Rev., 40, 672-687. 

Serwadczak, M. and Kucharski, S. (2006) Photochromic gratings in sol-gel hybrid materials containing cyanoazobenzene chromophores. /. Sol-Gel Set Technol,... 

Polyoxometalates are important catalysts but they are also finding application in optical, electrical, and magnetic devices. Mixed-metal polyoxometalates with vanadium(V) in the polyoxoanion core confers enhanced properties to such structures, principally in their ability to form essentially infinite networks that can be utilized as coatings or as other thin film materials. Additionally, these materials have tunable electromagnetic and photochromic properties. In combination with organic polymers, so-called hybrid polymers, special electrochemical properties are conferred, making possible such electrical storage devices such as capacitors and batteries that utilize the redox properties of the polyoxometalate [7],... 

Sapurina et al. have reported the synthesis of PANI-coated waterborne polyurethane latexes in the presence of a polymeric stabihzer, polyvinylpyrrolidone (PVP). The composite particles showed a conductivity of 10 S cm i, with good colloidal and mechanical properties [73]. Recently, Huang et al. synthesized a series of PPy-coated styrene-butyl acrylate (SBA) core-shell latex particles [74], The Tg of the composite particles was shown to be determined mainly by the core material. It was reported that the conductivity of the hybrid particles could be tuned by varying the butyl acrylate content in the SBA copolymer. The composite particles showed a conductivity of 0.17 S cm Composite particles having a photochromic dye as the core and ICP as shell, and possessing properties of photoluminescence, have been studied by Jang etal. [75]. Thin PEDOT-coated PS particles (Fig. 6.14) were reported for self-assembled crystalline coUoidal arrays with a stop band in the visible regime by Han and coworkers [76]. 

The hybrid approach to obtain photochromic materials with greatly improved properties from the point of view of potential applications is now being widely studied by many research groups [95-103]. 

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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