Twisted S1 excited state geometries in 4-dimethylaminobenzonitrile and dimethylaniline: New -d6 origin bands

Abstract

The S1←S0 electronic spectra of 4-dimethylaminobenzonitrile-h6 and -d6 (DMABN) and dimethylaniline-h6 and -d6 have been reexamined, and new electronic origins have been observed for the -d6 species, approximately 65 cm−1 lower in energy than previously reported. The spectra of DMABN-h3d3 and several other isotopomers of DMABN are reported for the first time. A prominent low-frequency progression is assigned to dimethylamino torsion, and the S1 states are found to be twisted by about 26° with a small 190 cm−1 barrier to planarity. Other bands are tentatively assigned to inversion and methyl torsional motions.