(4-ETHOXYPHENYL)UREA AS A FLUORESCENCE PROBE IN SOL-GEL PROCESSES

Measurement of the fluorescence of a sol-gel material during the trans ition permits monitoring of variations before and after the gelation p oint, per;ods for which other techniques show little signal variation. The excitation and emission spectra and the fluorescence lifetime of (4-ethoxyphenyl)urea (dulcin) were observed as a function of the time during the sol-gel-xerogel process of the tetraethyl orthosilicate sys tem, The spectra were compared to those obtained in environments of di fferent physical properties, The changes in lifetime of (4-ethoxypheny l)urea provide a sensitive probe of the structural changes that occur during the sol-gel process.