Specific deuterium isotope effects on the intramolecular charge-transfer dynamics of 4-(dimethylamino)benzonitrile

Abstract

The photoinduced charge-transfer (CT) dynamics of 4-(dimethylamino)benzonitrile (DMABN) are studied for methyl-deuterated isotopomers DMABN-d₆ (with two CD₃ groups) and DMABN-h₃d₃ (with one CH₃ and one CD₃ group) by steady-state and time-resolved fluorescence spectroscopy. The asymmetrically deuterated species DMABN-h₃d₃ is found to exhibit less CT fluorescence in sufficiently polar solvents than the symmetric isotopomers of DMABN-h₆ and DMABN-d₆. The results of fluorescence decay measurements are also reported, which suggest that the rate of backward electron transfer is increased upon asymmetric substitution of the dimethylamino group.