The triplet states of complexes with tetrachlorophthalic anhydride and phthalic anhydride as electron acceptors

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Abstract
Triplet-triplet (T-T) absorption, E.S.R., and phosphorescence spectra were observed for tetrachlorophthalic anhydride and phthalic anhydride complexes with methyl substituted benzenes. T-T absorption bands characteristic of electron donor-acceptor interaction, in addition to those pertinent to the component molecules, were found for the tetrachlorophthalic anhydride complexes. The observed T-T absorption spectra can be understood systematically by considering the interaction among zero-order charge-transfer triplet states and zero-order locally (within the acceptor) excited triplet states. From the analysis of the results of E.S.R. spectra, the CT characters of the lowest triplet states were obtained to be 80, 46, 37, and 26 per cent for the tetrachlorophthalic anhydride complexes with durene, mesitylene, toluene, and benzene, respectively, while the lowest triplet states of complexes of phthalic anhydride with mesitylene and toluene were found to have the character of local excitation within the acceptor.