Infrared absorption and resonance Raman scattering of photochromic triphenylformazans

Abstract

The infrared and resonance Raman spectra of the two long-lived forms of triphenylformazan and several of its derivatives have been examined. The spectra of unsymmetrically 15N-labelled derivatives suggest that two tautomers exist for each of the two forms. This observation is confirmed by the spectra of 1-(p-halophenyl)-3,5-diphenylformazans. The spectra of the non-chelate forms of these latter compounds demonstrate that the position of the tautomeric equilibrium is influenced by the electron-attracting ability of the para-halo-substituent. A comparison of the resonance Raman spectra of the two forms leads to the conclusion that excited state proton transfer is the initial photoevent in the photochromism of the triphenylformazans.