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A Theoretical Study of Benzene Dimers in the Excited States: Wavefunction Delocalization, Charge‐Transfer Admixture, and Electronic Coupling
Author(s) -
Kim Dongwook
Publication year - 2017
Publication title -
bulletin of the korean chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.237
H-Index - 59
ISSN - 1229-5949
DOI - 10.1002/bkcs.11168
Subject(s) - excited state , chemistry , delocalized electron , singlet state , ab initio , singlet fission , atomic physics , ground state , wave function , dimer , intermolecular force , molecule , excimer , configuration interaction , molecular physics , physics , quantum mechanics , organic chemistry , fluorescence
Ab initio calculations were carried out to investigate various benzene dimers, including T‐shaped ( T ), parallel‐displaced ( PD ), herringbone‐type ( Hb ), face‐to‐face eclipsed ( F2F ‐ E ), and face‐to‐face staggered ( F2F ‐ S ) configurations in the lowest singlet ( S 1 ) and triplet ( T 1 ) excited states. Monomer and dimer geometries in the excited states were optimized at the scaled opposite‐spin ( SOS ) CIS ( D 0 ) level of theory, and their energetics were compared. In PD and edge‐on type dimer configurations ( T and Hb ), the exciton wavefunctions are localized mainly within single benzene molecules, making intermolecular interactions in the excited states nearly the same as those in the ground state. On the other hand, both the cofacial dimers ( F2F ‐ E and F2F ‐ S ) in the excited states present substantial enhancements in the binding energies, approximately ranging from 0.12 to 0.55 eV , compared to the ground state. However, further analyses of electronic couplings between the frontier molecular orbitals of each molecule demonstrate the significant difference between such dimers; unlike in the F2F ‐ E dimer, in the F2F ‐ S configuration, the excimer formation arises from coupling between different states of each monomer, e . g ., the S 1 state of one molecule and the S 2 state of the other. In addition, for these cofacial dimers, the electronic coupling for triplet exciton is much weaker than that for its singlet counterpart, which can be rationalized by the different role of exchange energy in stabilizing respective states.