Kinetics of annihilation of triplet excitationsand decay of delayed fluorescence for isolated 1,12-benzoperylene pairs

We studied the annihilation kinetics for triplet excitations in isolated pairs of organic molecules and their delayed fluorescence decay using a new mathematical model for the process. According to this model, the intensity of delayed annihilation fluorescence (DAF) for isolated pairs is directly proportional to the number of pairs in which both molecules are found in the excited triplet state. We show that the decrease in such pairs and the decay of their delayed annihilation fluorescence occur according to an exponential law in the absence of random scatter in the deactivation rate constants for the triplet excitations. The results of an experimental study of the DAF decay kinetics for 1,12-benzoperylene in n-hexane at 77 K, where triplet–triplet annihilation occurs in isolated pairs, confirm the validity of the theoretical conclusions.