Resonances in mediated intersystem crossing of jet-cooled anthracene derivatives

The mechanisms of direct and mediated intersystem crossing from the first excited singlet manifold of anthracene and some of its derivatives were explored by the study of the internal and the external heavy-atom effect on the fluorescence quantum yields. Pronounced mode selectivity was observed in the vibrational energy dependence of the emission quantum yield in 9-bromoan-thracene and 9,10-dibromoanthracene.