Energy Transfer in Molecular Complexes. II. The Anthracene-sym-Trinitrobenzene Complex

The emission spectrum of the anthracene-sym-trinitrobenzene complex has been investigated in a solid solution in a diethylether-isopentane (EP) glass at 77°K. The observed luminescence consists of two distinct electronic transitions: one transition is the reverse of the charge-transfer E←N absorption of the complex; the other transition is a phosphorescence very similar to the T→S emission of anthracene in EP, but blurred somewhat in vibrational structure, blue shifted by 113 cm—1, decreased in lifetime by a factor of about 2 and showing decreases in the ground state vibrational frequencies of a few percent. These results, as opposed to previous conclusions (vide infra), would suggest that the phosphorescence is truly a T→S process of the complex which is largely localized on the anthracene component. Vibrational analyses of T→S spectra of anthracene in EPA and in EP and of the T→S and E→N spectra of the complex in EP at 77°K are given.