Role of the Comonomer GLYMO in ORMOSILs As Reflected by Nile Red Spectroscopy

The spectroscopy of nile red (NR) was reported when incorporated in organically modified silicates (ORMOSILs), obtained by the copolymerization of (glycidoxypropyl)trimethoxysilane and tetramethoxysilane in various proportions. An increase of the fluorescence intensity, a gradual blue spectral shift by 43 nm in absorption and 45 nm in emission, and a change in the lifetime from 2.6 to 4.4 ns of the dye were observed as a response to the change of the polarity and the structure of the ORMOSILs caused by the addition of (glycidoxypropyl)trimethoxysilane. The decrease of the nonradiative H + -NR form was observed as one of the consequence of addition of (glycidoxypropyl)trimethoxysilane. Absorption spectral shifts of the NR were used for the determination of a polarity empirical scale ( E NR ) of the ORMOSIL. The value of E NR ( r 0/100 ) = 48.70 kcal/mol for NR in silica xerogels prepared from tetramethoxysilane and E NR ( r 100/0 ) = 52.55 kcal/mol for NR in ORMOSILs prepared from (glycidoxypropyl)trimethoxysilane showed the high polarity of the inorganic matrixes in contrast to ORMOSILs. A study in solution was performed in order to make a concluding comparison of the NR behavior in terms of the restricted environment around the NR molecule ORMOSILs.