AN INVESTIGATION OF THE SOLVENT DEPENDENCE ON THE ULTRAFAST INTERSYSTEM CROSSING KINETICS OF XANTHONE

The photophysics of xanthone in solution are measured using femtosecon d pump-probe techniques. A kinetic model which includes intersystem cr ossing from both the (1) pi pi and (1)n pi* electronic states accurat ely represents the non-single exponential growth of the triplet-triple t absorption after excitation into the (1) pi pi state at 310 nm. The intersystem crossing rate constants are consistent with an 'inverse' gap effect due to solvent polarity induced shifts in the electronic st ates. The branching between intersystem crossing from the (1) pi pi a nd (1)n pi electronic states is also solvent dependent and is determi ned by the rate constant for internal conversion in the singlet electr onic state.