Synthesis, electronic structure and NH-tautomerism of novel mono- and dibenzoannelated phthalocyanines

Novel low-symmetry benzoannelated metal-free phthalocyanines of A3B-, ABAB- and AABB-types were synthesized by statistical condensation of phthalonitrile bearing bulky solubilizing groups (fragment A) and new naphthalonitrile with OH-terminated diethylene glycol anchors (fragment B). Comprehensive physical-chemical characterization of the synthesized macrocycles allowed to reveal the electronic effects associated with the extension of π-system. The interpretation of the observed effects was performed by theoretical calculations where simplified TD-DFT approach at CAM-B3LYP/6-31G(d) level was successfully used for the first time to predict excitation energies of Q-band region in UV–Vis spectra of low-symmetry phthalocyanines with errors not exceeding 0.03 eV. Altogether it allowed to identify the spectroscopic signatures of various tautomers including energy-unfavourable forms.