Time-resolved study of the photochemical reaction of 4-dimethylaminobenzonitrile with carbon tetrachloride

The mechanism of 4‐dimethylaminobenzonitrile (DMABN) fluorescence quenching by carbon tetrachloride was studied using time‐resolved fluorescence, absorption and Raman techniques. Picosecond and nanosecond time‐resolved Raman spectra of DMABN and DMABN‐d6 were obtained in resonance with different electronic states to identify intermediates, their structure and time‐dependent dynamic changes. The quenching is attributed to intermolecular electron transfer between B‐state DMABN and carbon tetrachloride with a time constant of ∼500 fs leading to the formation of the DMABN radical cation as the initial intermediate followed by a ∼13 ps process yielding a DMABN Cl adduct as product with a lifetime longer than 50 ns. It is likely that the chlorine atom is located at the amino para‐ring position of the highly reactive DMABN radical cation. It is suggested that this reaction mechanism is general for other donor–aromatic–acceptor type DMABN derivatives. Copyright © 2001 John Wiley & Sons, Ltd.