Computations have been performed for the singlet and triplet electronic sta
tes of varying orientations of naphthalene dimer. The dependence of exciton
splitting upon orientation and intermonomer distance was explored. Splitti
ngs of triplet states are seen to be nontrivial at typical bonding distance
s, commensurate with the splittings of weakly allowed singlet states. Charg
e-transfer interaction with the excimer states is seen to be most significa
nt 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 r
adiative and nonradiative decay of the T-1 triplet state of the monomer, an
d then applied to the dimer. The mechanism has been found for the observed
more rapid phosphorescence of the T-1 state of the dimer when placed in ori
entations lacking inversion symmetry. (C) 2000 American Institute of Physic
s. [S0021-9606(00)00244-0].