Fine-structure vibronic spectra and NH-phototautomerism in free-base unsubstituted 2,3-naphthalocyanine in naphthalene at 6 K

Spectral-luminescent investigations of free-base unsubstituted 2,3-naphthalocyanine (2,3-NcH2) in naphthalene and tetrakis(tert-butyl)-derivative of 2,3-NcH2 in various solvents at room temperature, 77 and 6 K have been carried out. An essential dependence of the S2-S1 energy interval of the compounds investigated, ΔES2S1, on the nature of the matrix environment has been found (the values of ΔES2S1 lie within the limits 100 and 300 cm−1). At 6 K the fluorescence spectrum of 2,3-NcH2 has a well-resolved vibrational structure under broadband excitation, resulting practically from the emission arising from two main sites and therefore consisting of “doublets” of narrow lines. The qualitative analysis of the vibrational structure of the fine-structure fluorescence spectra of 2,3-NcH2 enabled assessment of the form of active modes. For the two main sites efficient NH photoisomerization of the 2,3-NcH2 molecules under selective laser excitation has been established.