Isothermal and Photostimulated Emissions of Indole and Tryptophan in Two Polar Matrices at 77 °K

Abstract

The isothermal delayed fluorescence along with the visible photostimulated fluorescence and phosphorescence emissions have been recorded and studied for the following systems: a 10−3 M solution of indole in an ether glassy matrix, a 10−3 M solution of indole in an ethylene glycol–water glassy matrix (EG–W) (70–30 by volume), a 10−3M solution of tryptophan in an EG–W glassy matrix (70–30 by volume). All these experiments have been performed at the temperature of liquid nitrogen. It has also become possible to record the action spectra of the photostimulated emissions which give us information about the entities playing an active part in the recombination processes. The electron–cation recombination after visible light stimulation has been analyzed in terms of a kinetic model based on the assumption that upon neutralization an intermediate state is formed from which the molecule decides what its spin multiplicity will be. It was found that in an EG–W glass at 77 °K about 80% of the recombination events lack the energy necessary to reach the first excited singlet state of the amines studied. In an ether glass this percentage decreases to about 28%. This result is qualitatively in accord with the fact that the photostimulated electrons are more stabilized in an EG–W glass by an amount of energy equal to 1.5 eV.