The Triplet States of 1,3,5-Tricyanobenzene Complexes with Methyl Substituted Benzenes

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Abstract
Triplet-triplet absorption, phosphorescence, and ESR spectra have been measured on the 1,3,5-tricyanobenzene complexes with toluene, mesitylene, durene, and hexamethylbenzene. Four triplet-triplet absorption bands were commonly observed in the wave number region of 10000–30000 cm−1 for all the complexes. The observed phosphorescence and T-T absorption spectra could 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 an analysis of the zero-field splitting values obtained from the observed ESR spectra, the contribution of the zero-order charge-transfer triplet state to the lowest triplet state was determined to be 76,65,25, and 9% for the 1,3,5-tricyanobenzene complexes with hexamethylbenzene, durene, mesitylene, and toluene, respectively. From the consideration on the results obtained for various polycyanobenzene complexes, the phosphorescence lifetime was found to decrease remarkably for the complexes with the charge-transfer character higher than 50% in their lowest triplet states.