Phosphorescence and spin polarization

Abstract

Intersystem-crossing in aromatic molecules is caused by spin-orbit coupling. This mechanism is expected to be highly selective for a specific spin-component of each triplet state. Experimental evidence is given for quinoxaline proving that spin polarization indeed occurs when this molecule is optically excited into its lowest triplet state. A remarkable coherence phenomenon, reminiscent of level-crossing situations in atomic spectroscopy, seems to be observed following flash excitation in a magnetic field.