Matrix effects and mechanisms of the spectral shifts of coumarin 440 dopedin sol-gel-derived gel glass

The spectral and temporal changes of the emission from four types of gel gl ass doped with coumarin 440 prepared by using tetraethoxysilane (TEOS), 3-g lycidoxypropyltrimethoxysilane (GPTMS), methyltriethoxysilane (MTES), and v inyltriethoxysilane (VTES) as sol-gel precursors, respectively, were studie d. The observed significant spectral shifts of coumarin 440 in the TEOS- an d TEOS/GPTMS-gel glass are due to two types of matrix effects on different time scales. The formation of hydrogen bonding between the carbonyl and ami ne groups of coumarin 440 and the residual Si-OH and H2O in the TEOS- and T EOS/GPTMS-gel glass shifts the emission spectra to longer wavelengths on th e subnanosecond time scale with respect to that in the MTES- and VTES-gel g lass. The temperature and time dependent spectral shifts on the nanosecond time scale are attributed to the reorientation of the surrounding matrix mo lecules during the lifetime of the excited state of coumarin 440. No residu al Si-OH groups H2O molecules are found in the MTES- and VTES-gel glass pre pared by acid-catalyzed hydrolysis and basic-catalyzed condensation, and th e emission spectra of coumarin 440 in these matrices show no dependence on time and temperature. (C) 2000 American Institute of Physics. [S0021-8979(0 0)01817-X].