TWISTED INTERNAL CHARGE-TRANSFER IN (AMINOPHENYL)PYRIDINIUM

The electron donor dimethylaniline and the electron acceptor methylpyridinium are coupled with a twistable bond as [(dimethylamino)phenyl]methylpyridinium and in the rigid frame of fluorene as (dimethylamino)methylazafluorenium. The fluorescence of both chromophores is studied. The quantum yield of the rigid dye is around 50%. The quantum yield of the twistable homolog is low. It drops to about 0.05% in solvents of high polarity and fluidity. The difference is assigned to the formation of a TICT state (twisted internal charge transfer) with efficient radiationless deactivation.