The Incorporation and Thermal Stability of Organic Dyes in Dialkylsiloxane-Oxide Matrices
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Materials Engineering Department, Center for Glass Science and Technology, Rensselaer Polytechnic Institute, Troy, NY 12180-3590. 2 Current address: Battelle, Pacific Northwest Laboratories, Richland, WA 99352. 3 Current address: United Technologies Research Center, East Hartford, CT 06108. 4 Chemical Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12180-3590. ABSTRACT The dyes oxazine 725, 7-acetoxy-4-methyl coumarin, 0-4-methylcoumarinylN-[3-(triethoxysilyl)-propyl] carbamate and 2',7'-dichlorofluorescein were introduced during the acid-catalyzed cohydrolysis of various molar ratios of tetraethoxysilane (TEOS) and the gel modifers, diethoxydimethylsilane (DEDMS) or diethoxymethylvinylsilane (DEMVS). The morphological features and optical absorption spectra of the resulting dye doped gels were followed during subsequent drying and heating. For DEDMS-TEOS molar ratios less than 1.375, gel cracking during drying was a problem. DEDMS-TEOS molar ratios greater than 2.750 yielded optically transparent monoliths, but did not allow for sufficient incorporation of dye to be useful. However, the functionalized dye, O-4-methylcoumarinyl-N-[3(triethoxysilyl)-propyll carbamate, appeared to be significantly more soluble in such a highly modified matrix. Compared to matrices derived from pure TEOS the DEDMS or DEMVS modified matrices provided oxazine 725 doped with improved thermal stabilities.
Finally, the 2',7'-dichlorofluorescein doped dimethylsiloxane-
oxide matrix showed good thermal stability in its optical properties, having significant optical absorption and little change in the wavelength of the absorption maximum after heating to 300'C. INTRODUCTION In a previous article by Darab and MacCrone [1] it was reported that certain
sites of dopant incorporation within a silica sol-gel matrix provide thermal and environmental protection to solvated copper(II) complexes.
Others have reported
the incorporation of optically active organic species into matrices consisting of inorganic oxide gels and polymer/oxide composite gels [2,3]. These materials are useful in applications involving advanced optical coatings, for example. However, in the as prepared condition, the optical properties of such materials are susceptible to environmentally and temporally induced variations. Although, heating these materials might stabilize their properties to some extent, relatively little work has focused on the behavior of these systems to temperatures above 150 0C [1,3]. In this study we explored the doping of organic dyes into sol-gel derived siloxane-oxide
matrices and and their optical stability after heating to temperatures of up to 350'C. 547
Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
Babonneau and coworkers [41 previously reported structural evidence for the copolymerization of DEDMS and TEOS. A similar cohydrolysis technique was employed in this work in order to produce monolithic optical components, which can readily be accomplished by cohydrolyzing TEOS with alkoxyalkylsilanes [4].
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