Time-resolved study of the triplet state of 4-dimethylaminobenzonitrile (DMABN)

Abstract

Nanosecond time-resolved resonance Raman spectra of the triplet states of DMABN, DMABN-d 6, and DMABN-N 15 have been obtained over the frequency range from 700 to 2300 cm -1. Isotopic shifts identify modes associated with the dimethylaniline subgroup. There is no significant difference between spectra recorded in polar and nonpolar solvents implying that the lowest triplet state ( 3T 1) state has only one form. Our results characterize it as planar or near planar in structure, with a high negative charge localization on the cyano group and a substantial loosening of the ring skeleton with conjugation extending to the amino group. Nonradiative deactivation of the singlet intramolecular charge transfer state ( 1ICT) through intersystem crossing is discussed in relation to the transient absorption spectra.