Near‐infrared fourier transform Raman spectroscopy of indigoids

Abstract

Abstract Near‐infrared Fourier transform Raman spectra (3400 to — 20 cm −1 ) for the solid phases of indigo, thioindigo, selenoindigo and N,N '‐dimethylindigo were recorded with excitation using Nd:YAG laser radiation at 1064 nm. A complete vibrational assignment is proposed supported by the results of ab initio calculations. The spectra are complementary to the IR spectra recorded earlier. They also complete earlier results of resonance Raman spectroscopy. The spectra support a molecular structure of the indigo chromophore with a cross‐conjugated vinylogue amide system.