The effect of MTMS on the optical properties of TEOS synthesized gels doped with thionin

Thionin doped silicate gels, initially synthesized with tetraethyl orthosilicate (TEOS), were modified by incorporating a second precursor, methyltrimethoxysilane (MTMS). The optical spectra revealed the formation of a second band in thionin gels containing over 50% MTMS. These new bands for the absorption and fluorescence spectra were found to reside at 560 nm and 665 nm, respectively. According to the behavior of thionin dissolved in aqueous solutions, it was readily deduced that these newly formed peaks were a result of dimers. Furthermore, FTIR spectroscopy revealed that gels synthesized with MTMS possess a significantly lower concentration of Si-OH groups than gels prepared from TEOS. Due to the reduction in Si-OH concentration, the polarity of the gel was decreased which accounted for the blue shifts in the fluorescence spectrum of thionin doped gels synthesized with raised MTMS contents. Finally, dye aggregation was suggested to be the result of fewer sites provided by the organically modified gels.