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Donor-Acceptor Interaction and Photochemistry of Polymethylene-Linked Bichromophores in Solution

The ground-state and the excited-state spectroscopic properties of four series of polymethylene-linked anthracene−dialkylaniline bichromophores were compared as a probe to the relationship between energetics and distance in photoinduced electron transfer (PET). The results demonstrate that, when the energy level of the charge-transfer (CT) state is lowered below that of the localized excited state by appropriate substituents, there is a strong electron−donor−acceptor (EDA) interaction in the ground state which is absent in other bichromophores. Absorption and fluorescence excitation studies revealed that there is an unusually strong EDA interaction in the ground state of A-2 which is absent in other members in the A series. When A-2 is excited directly into this EDA absorption, it exhibits two CT emissions, one at 490 nm and the other at 605 nm. The quantum yield (τf) and the lifetime (Φf) of the two emissions are dependent on the viscosity of the alkane solvent. The Φf and the τf of the 490 nm emission i...