Photochromism in spiropyran impregnated fluorinated mesoporous organosilicate films
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Fluorinated mesoporous organosilicate films were synthesized by sol-gel spincoating on a quartz substrate using (heptadecafluorodecyl)trimethoxysilane, tetramethylorthosilicate, and n-cetyltrimethylammonium chloride as the fluoro-precursor, silica source, and supramolecular template, respectively. The photochromism efficiency of photochromic dyes (spiropyran) increases in the order non-porous < hexagonal mesoporous < fluorinated mesoporous organosilicate films. The relatively high efficiency of the photochromism of spiropyran in fluorinated mesoporous organosilicate films suggests that such films are promising materials for applications as optical shutters and light modulators.
I. INTRODUCTION
Scientists at Mobil Corporation (Poulsboro, NJ) synthesized silica-based mesoporous molecular sieves with hexagonal, cubic, and lamellar structures called M41S materials in 1992.1 These materials have high surface areas, ordered pore mesostructures, and uniform pore sizes. Mesoporous silica thin films show promise in applications such as membrane separations, chemical sensors, optical devices, and electronic devices such as low-k dielectric films.2–4 Mesoporous thin films can be formed by spin coating or dip coating in what is called evaporation induced self-assembly (EISA).5–7 By changing the ratio of surfactant to silica precursor solutions, the silica films were found to acquire lamellar, hexagonal, or cubic mesostructures.8,9 Early attempts to incorporate guest species in the mesoporous sorbent MCM-41 resulted in low guest loadings, probably due to the absence of specific interactions between the host mesoporous materials and guest molecules. The use of organically functionalized mesoporous materials may alleviate this problem, and the synthesis of inorganic-organic hybrid mesoporous silica has recently been reported.10 Chemical functionalization of the inorganic framework of porous materials, for example through the covalent coupling of an organic moiety, is a promising approach to specific pore surface properties
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0315 J. Mater. Res., Vol. 19, No. 8, Aug 2004
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such as hydrophobicity, polarity, and catalytic, optical, and electronic activity.11,12 In the present study, optically transparent and crackfree fluorinated mesoporous organosilicate films have been synthesized by sol-gel spin-coating on a quartz substrate using (heptadecafluorodecyl)trimethoxysilane, tetramethylorthosilicate, and n-cetyltrimethylammonium chloride as the fluoro-precursor, silica source, and supramolecular template, respectively. Photochromic materials, which change their color reversibly in response to light, can be applied to optical waveguides, shutters, light modulators, and optical storage media when these dyes are incorporated into appropriate matrices.13,14 For optical applications, a high photochromism efficiency is required.15 For this purpose, a wide range of chemically various matrices,
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