Influence of Aza-Substitution on Molecular Structure, Spectral and Electronic Properties of t-Butylphenyl Substituted Vanadyl Complexes

Vanadyl octa-(4-<i>tert</i>-butylphenyl)phthalocyanine (<b>VOPc(<i>t</i>-BuPh)₈</b>) and vanadyl octa-(4-<i>tert</i>-butylphenyl)tetrapyrazinoporphyrazine (<b>VOTPyzPz(<i>t</i>-BuPh)₈</b>) complexes were synthesized for the first time and confirmed by IR and UV-Vis spectroscopy and MALDI-TOF spectrometry. The method of synthesis of their precursors, 4,5-bis(4-<i>tert</i>-butylphenyl)phthalonitrile (<b>(<i>t</i>-BuPh)₂PN</b>) and 5,6-bis(4-<i>tert</i>-butylphenyl)pyrazine-2,3-dicarbonitrile (<b>(<i>t</i>-BuPh)₂PDC</b>), was modified, resulting in higher yields. For the vanadyl complexes, the basic properties were studied, and it was found that the red shift in the Q band in the first protonation step is approximately two times greater than that of previously known complexes. An electrochemical study showed the influence of aza-substitution on the redox properties and on the energies of the frontier orbitals of all the compounds presented. For all four considered compounds, quantum chemical calculations of the molecular structure, IR spectra, and electronic absorption spectra were carried out using density functional theory (DFT) and time-dependent density functional theory (TDDFT and simplified sTDDFT) approaches. According to the DFT calculations, vanadyl macrocyclic complexes have dome-shaped distorted structures. Experimental and theoretical IR and electronic absorption spectra were compared and interpreted.