The conformations and exciton couplings in 5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene (THDC) have been studied using resonance-enhanced two-photon ionization spectroscopy in a supersonic jet expansion. It has been estimated from the spectral analysis that 90% of THDC exists in the twist-boat (TB) conformation; the chair (C) conformer constitutes the remaining 10%. Most of the vibronic activity in the spectrum of THDC is associated with the symmetric flapping of the aromatic rings of the TB conformer. The observed S 1 /S 2 exciton splitting of the TB conformer is 100 cm -1 . The S 1 /S 2 transition of the C conformer is found to be forbidden. The exciton splittings of the C and TB conformers were estimated by the spectral analysis of two deuterated isotopomers of THDC. The estimated exciton splittings of the C and TB conformers are 14.7 and 101.9 cm -1 , respectively. The supramolecular model of bichromophores with identical chromophores at the CIS/6-31?G(d)//HF/6-31?G(d) level of theory predicted electronic coupling energies that are very close to the experimental exciton coupling energies.
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