Naphthalene character and absence of the CO stretching vibration in the resonance Raman spectrum of 2-naphthaldehyde in its lowest ππ* triplet state

Abstract

The CO stretching vibration dominates the ground-state Raman spectrum of 2-naphthaldehyde. The present study of the resonance Raman spectra of 2-naphthaldehyde and of various isotopically labelled 2-naphthaldehydes in the lowest ππ* triplet state, reveals the absence of lines due to vibrational modes involving displacements of atoms in the aldehyde group. All the lines in the triplet-state Raman spectra may be assigned satisfactorily to modes involving only displacements of atoms in the naphthyl group of the triplet-state molecule. This result supports the view that there is no conjugation between the naphthyl and the aldehyde group in the triplet state concerned. The synthesis of the isotopically labelled compounds is described.