Electronic spectra of the naphthyridines: 2,7-naphthyridine

Abstract

The first detailed study of the electronic spectrum of 2,7-naphthyridine is reported. Absorption and emission spectra were recorded of 2,7-naphthyridine in solution, vapour phase, and in various mixed-crystal systems. Infrared and Raman spectra were also recorded, and used to assign the normal vibrational modes of the molecule so that the vibronic structure of the electronic spectra could be assigned. The spectra have some unusual features, but may be interpreted with the help of semiempirical molecular-orbital calculations. The lowest-energy π* ← n band system in the absorption spectrum is consistent with theoretical predictions, and the π* ← π band systems correspond to slightly perturbed naphthalene transitions. The phosphorescence spectrum is caused by a 3(π*,π) state and yields useful vibrational information.