Luminescence of Sterically Hindered Arylethylenes

Abstract

AbstractTemperature dependence of fluorescence spectra and fluorescence polarization has been measured on a number of arylethylenes. The fluorescence maximum of those molecules showing steric hindrance abruptly shifts to higher energy during glass formation of the solvent. The polarization, however, only slightly increases with increasing viscosity. This effect can be understood in terms of intramolecular relaxation processes of the torsional vibration around the ethylenic double bond. – Despite of high steric crowding some arylethylenes exhibit fluorescence emission even at room temperature. The lifetimes of the related excited singlets are markedly reduced (about 10−11 sec) as estimated from polarization measurements.