The microstructural dependence of intramolecular photoautomerism of salicylic acid doped in silica gel glass prepared by a sol-gel process

Many fluorophores will show photoautomerism if irradiated by light, which r esults in some changes of the fluorescence emission spectra of these fluoro phores. The intramolecular photoautomerism of salicylic acid in silica gel glass prepared by a sol-gel process and an ethanol solution were studied co mparatively. Doped in silica gel glass, salicylic acid, as well as water an d ethanol, co-exists in the pores of the gel glass, and only one broad band due to the zwitterion is observed and shifts to longer wavelength with res pect to that in ethanol solution as a result of solvent effects. After the doped gel glass being heat treated at 150 degrees C, some salicylic acid mo lecules are trapped in the tiny pores with little polarity, and the broad b and around 370 nm due to the neutral molecule appears. The number of salicy lic acid molecules trapped in the low polar pores of the gel glass increase s after the sample is heat treated at elevated temperature, which increases in the fluorescence intensity of 370 nm emission band. (C) 1999 Elsevier S cience B.V. All rights reserved.