Theoretical study on the excited-state photoinduced electron transfer facilitated by hydrogen bonding strengthening in the C337–AN/MAN complexes

Significant intermolecular hydrogen bonding strengthening in the excited state is proposed to facilitate the photoinduced electron transfer process from the electron donating solvents aniline (AN) and N-methylaniline (MAN) to the coumarin dye 337 (C337). Time-dependent density functional theory (TD-DFT) method has been applied to investigate the ground and the two lowest singlet excited states of the hydrogen-bonded C337–AN and C337–MAN compounds, with a view to monitoring their geometries and photochemical properties. The present theoretical study indicates that the PET process which occurs in the lowest singlet excited state S1 after the full relaxation of the hydrogen-bonded complex in the S2 state should be coupled with and facilitated by the significant strengthening of the intermolecular hydrogen bonding.