The Study of the Intramolecular Heavy Atom Effect in 9,10-Dichlorophenanthrene and 1,2,3,4-Tetrachloronaphthalene Using PMDR Techniques.

The heavy atom effect in triplet 9,10-dichlorophenanthrene and 1,2,3,4-tetrachloronaphthalene is investigated by PMDR techniques. As in the parent hydrocarbons, spin-orbit and spin-orbit vibronic mechanisms are invoked to explain the results. The relative radiative rates of the triplet zero-field levels are determined by static distortions of the chlorine atoms, while the intersystem crossing rates from S1 are mainly governed by the enhancement of spin-orbit vibronic coupling via C-C1 out-of-plane modes that mix the relevant sigma, pi and pi,pi states. In both processes the top two levels tauA and tauB are more active, with TauB the most favoured of the two. Author