Significant quenching of the photoinduced charge separated state of aminophenyl(phenyl)acetylene and N,N-dimethylaminophenyl(phenyl)acetylene in protic solvents

By using picosecond transient absorption and fluorescence lifetime measurement techniques, we have investigated intramolecular charge separation and charge recombination processes of aminophenyl(phenyl)acetylene and N,N-dimethylaminophenyl(phenyl)acetylene in various polar solvents. Significant quenching of the intramolecular charge separated state was observed in protic solvents and both the triplet and fluorescence yields were much lower than those in aprotic polar solvents. Such enhancement of the charge recombination was explained by the increase of the radiationless transition probability to the ground electronic state caused by the structural deformation around the amino nitrogen atom. Interaction between the amino nitrogen atom and the oxygen atom of the solvent molecule, which is the hydrogen-bond donor terminal of the network, should play an important role.