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-d6were 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.