CHEMICALLY-INDUCED DYNAMIC ELECTRON POLARIZATION (CIDEP) IN SYSTEMS INVOLVING RADICAL-ION PAIRS GENERATED FROM SINGLET EXCIPLEXES - OBSERVATION OF POSITIVE ELECTRON EXCHANGE INTERACTIONS

The CIDEP spectra from the photolysis of solutions containing pyrene and anthracene (separately) in the presence of various electron donors and acceptors, in which radical-ion pairs are formed from exciplex precursors, are reported. Reaction proceeds through the excited singlet states of the radical precursors and in all cases the polarization pattern indicates that the electron exchange interaction in these charged pairs is positive. 'The observations are affected strongly by degenerate electron exchange (electron hopping) processes. The results have been analyzed in detail using both Bloch equation and stochastic Liouville equation approaches, and the two are compared. It is shown that the former provides an inadequate description when exchange processes are sufficiently fast to affect spin evolution within the geminate cage.