External heavy atom effect on the triplet state of aromatic hydrocarbons. IV

The phosphorescence decay functions and spectra of ethanol solutions of triphenylene-d12, coronene and fluorene were observed in the presence of different KI concentrations at 77 K. The analysis of the dependence of phosphorescence (T1 → S0) rate constant, ksub(PT), and intersystem crossing (T1 → S0) rate constant, ksub(GT), on triplet energies Esub(T) of aromatic molecules and on the distance between the heavy atom and the aromatic molecule show that the external heavy atom effects on ksub(PT) and ksub(GT) are essentially of the second and third order, respectively. The phosphorescence spectra of triphenylene and coronene show the presence of the third order contributions in the radiative transition which involves the second triplet state of aromatic molecule. (Auth.)