Determination of the nature of the lowest triplet state of the intramolecular charge-transfer probes DMABN and DMABA by laser-induced optoacoustic spectroscopy

The possible electrostatic volume constriction associated with the excited state photophysics of the triplet states of the intramolecular charge transfer probes p-N,N-dimethylaminobenzonitrile and p-N,N-dimethylaminobenzaldehyde has been studied in apolar media by laser-induced optoacoustic spectroscopy, using a series of normal alkanes ranging from pentane to hexadecane as solvents. A nanosecond laser was used for excitation and the optoacoustic signal was determined by a piezoelectric transducer. Hardly any volume change is observed, suggesting that, in these solvents, the lowest triplet states of both p-N,N-dimethylaminobenzonitrile and p-N,N-dimethylaminobenzaldehyde do not have appreciable charge transfer character.