Resonance Raman and FTIR spectra of Mg-porphyrazines

• Resonance Raman spectra of porphyrazine derivatives were recorded.
• Spectral assignments of the vibrational modes have been proposed.
• Noticeable changes in the spectral features due to aza-substitution were established.
• Special features due to the presence of the aryl rings have been discussed.

Resonance Raman spectra (RRS) of Mg-tetraazaporphyrin (1) and Mg-tetraazaoctaphenylporphyrin (2) in solid crystal powder at ambient temperature and different excitation wavelengths were recorded and analyzed. FTIR spectra of 1 and 2 in solid crystal powder were also measured. On the basis of DFT quantum-chemical calculations the frequencies, maximum amplitude changes for internal coordinates, and the symmetry of the normal modes were calculated. The analysis of the experimental data and the results of quantum-chemical calculations allow us to carry out the assignment of modes manifested in the Raman and IR-spectra of 1 and 2 to the calculated set of vibrations. Differences in the orientation of the aryl rings of 2 and their modes manifestation in the spectra were identified and compared to metalloporphyrins with phenyl groups in meso-positions. An explanation for the spectral changes upon substitution in β-positions of pyrrolic rings by phenyl units is given, providing further elucidation of the structural features arising upon progressive substitution by phenyl groups for the design of new types of dendrimers.