Theoretical Studies of Transannular Interactions. II. The Triplet States of the Paracyclophanes

The triplet transition energies of benzene dimers at different inter-ring separations have been calculated, and the results used to interpret the phosphorescence spectra of the paracyclophanes. The transannular interaction is reflected in the energy of both the ground and excited states of the dimer. In the calculation of the latter, the configuration interaction of neutral-exciton and charge-transfer states is taken into account. The results of the calculation, which predict the lowest dimer state to be of benzene 3p parentage, are discussed in relation to the phosphorescence of [2,2] and [4,4] paracyclophane, which spectra are also reported in this paper. Good agreement between the calculated and observed transition energies is found.