Intramolecular charge transfer and exciplex formation in anthracene bichromophoric compounds

A binary compound containing strong electron donor and acceptor groups, (N,N-dimethylanilino)-CH2-9-cyanoanthracene (II), was synthesized, and its photophysical behaviour was studied. Intramolecular exciplex emission was observed in non-polar and moderately polar solvents, but not in polar solvents. Exciplex formation in non-polar and moderately polar solvents accounts for the exothermic electron transfer reaction and/or the efficient coupling of the amine lone pair with 9-cyanoanthracene pi orbitals; in polar solvents, the molecular structure corresponds to a solvent-separated radical ion pair formed by intermolecular electron transfer, where the energy is dissipated via back electron transfer (BET) without fluorescence emission. A new, blue-shifted emission at 510 nm appears in the region of the local emission band for compound II at 77 K, which may originate from a ground state, charge transfer (CT) conformer. The dependence of exciplex formation on the solvent and temperature is discussed by comparison with the compound (N,N-dimethylanilino)-CH2-anthracene (I), and a simplified energy diagram showing intramolecular charge transfer and exciplex formation in compounds I and II is described.