Transparent polysilsesquioxane films obtained from bridged ureasil precursors: Tunable photoluminescence emission in the visible region and filtering of UV-radiation

Abstract

Bridged ureasil precursors were synthesized by the reaction of either ethylenediamine (1 mol) or m-xylylenediamine (1 mol) with isocyanatepropyltriethoxysilane (2 mol). Transparent polysilsesquioxane films were obtained by the hydrolytic condensation of the pure precursors or their co-condensation in a 50:50 molar ratio. Films based on pure ureasil precursors showed a blue photoluminescent emission band assigned to the photoinduced proton-transfer among H-bonded urea groups and the subsequent radiative recombination of ionized groups. Films synthesized by the co-condensation of both precursors exhibited a significant red-shift of their absorption, excitation, and emission spectra, associated to de-localization of H-bonds, and a high absorption of UV-radiation. Polysilsesquioxane films synthesized by the co-condensation of two different ureasil precursors with similar lengths of organic bridges showed a significant red-shift of their absorption, excitation, and emission spectra when compared to films synthesized from a single ureasil precursor. They also exhibited a high absorption of UV-radiation while keeping transparency in the visible region.