Kinetics of the phosphorescent triplet states of electron donor-acceptor complexes as studied by microwave-induced delayed phosphorescence

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Abstract
With the aid of microwave-induced delayed phosphorescence, zero-field splitting patterns and the populating and depopulating rate constants of the individual spin sublevels were determined for the phosphorescent triplet states of 1,2,4,5-tetracyanobenzene (TCNB) and its electron donor-acceptor complexes with benzene, p-xylene, durene, pentamethylbenzene, and hexamethylbenzene in n-hexane at 1·25 K. From the analysis of the observed kinetic data, we obtained the minimum and maximum values for the radiative and non-radiative decay rate constants of the individual spin sublevels in the phosphorescent states of TCNB and its complexes. These values showed that a non-radiative decay process from the shortest lifetime sublevel is primarily responsible for the shortening of the phosphorescence lifetime due to complex formation.