Naphthalene dimer: Electronic states, excimers, and triplet decay

Computations have been performed for the singlet and triplet electronic states of varying orientations of naphthalene dimer. The dependence of exciton splitting upon orientation and intermonomer distance was explored. Splittings of triplet states are seen to be nontrivial at typical bonding distances, commensurate with the splittings of weakly allowed singlet states. Charge-transfer interaction with the excimer states is seen to be most significant in face-to-face orientations which can allow closer approach of the two monomers. Predictions of the prominent features of the singlet–singlet and triplet–triplet absorption spectra agree well with experimental findings. A spin-orbit channel-counting scheme is introduced to account for observed radiative and nonradiative decay of the T1 triplet state of the monomer, and then applied to the dimer. The mechanism has been found for the observed more rapid phosphorescence of the T1 state of the dimer when placed in orientations lacking inversion symmetry.