The E.S.R. and phosphorescence spectra of some dicyanobenzene complexes with methyl-substituted benzenes

Abstract The E.S.R. and phosphorescence spectra of the lowest excited triplet states of some charge-transfer complexes containing phthalonitrile, isophthalonitrile and terephthalonitrile as electron acceptors have been measured. Hexamethylbenzene, pentamethylbenzene, durene and mesitylene were used as donors. From the observed zero-field splitting constants, D*, the charge-transfer degree, x, in the lowest excited triplet states of these complexes was obtained. For example, x for the phthalonitrile-hexamethylbenzene complex is 0·48. For a fixed acceptor a decreasing order in x was found to go with an increasing order in the ionization potential of the donor.