Identification of the mechanism of enhanced exciton interaction in rigidly linked naphthalene dimers.

Recently we characterized the low-lying electronic excitations of H-aggregated perylene bisimide (PBI) dyes using the time-dependent long-range-corrected density functional theory (TD-LRC-DFT) and the mixed intramolecular Frenkel exciton (FE) and the intermolecular charge-transfer exciton (CTE) model (F. Pan, F. Gao, W. Z. Liang and Y. Zhao, J. Phys. Chem. B, 2009, 113, 14581.). We found that the dimer absorption follows closely the spectra of PBI aggregates in solution, and demonstrates strong mixing of two kinds of excitons. Here we implement the theoretical approaches to study the electronic excitations of a family of bridged naphthalene dimers. It is found that TD-LRC-DFT reproduces all experimentally observed trends in the absorption profiles. By comparing the results obtained from the popular hybrid exchange-correlation functionals with these from LRC-DFT, we display how the experimentally measured dipole-allowed mixed exciton states of systems are formed. The major terms which contribute to the experimentally measured dimeric splitting are qualitatively identified. Three-dimensional plots of transition charge density help visualize how the excitons couple.