The electronic structure of 4-(N,N-dimethylamino)-4′-cyano-biphenyl and its planar and twisted model compounds Original Research Article

The electronic structure of 4-(N,N-dimethylamino)-4′-cyano-biphenyl and its planar fluorene and twisted 2,6-dimethyl-substituted model compounds is analyzed by experimental means of UV/VIS absorption spectroscopy including linear dichroic and derivative spectra. CNDO/S-CI calculations show that the electronic structure of the biphenyls investigated can be approximately described within a composite-molecule model based on the 1Lb, 1La states of the dimethylaniline and benzonitrile subunits. But in addition to unsubstituted biphenyl (BP), an intramolecular charge transfer (CT) state is active as the first excited singlet state and the twist angle dependent interaction with the higher lying, locally excited singlet states modifies the absorption spectra. The A, B, C and H absorption bands of unsubstituted biphenyl can be correlated with the absorption spectra of the donor—acceptor biphenyls and the additional absorption band at fairly lower energy than the A band in biphenyl is assigned to a strong intramolecular CT band. This leads to a consistent and helpful interpretation of the electronic structure of donor—acceptor biphenyls including those investigated already in literature.