Theoretical exploration on the aromaticity regulation of prophyrazine by (de)protonation and (de)hydrogenation

Deprotonation/protonation is crucial characteristics of porphyrins and porphyrinoids solutions, and dehydrogenation/hydrogenation is also a common reaction in porphyrinoids synthesis as well. These processes fundamentally impact the molecular configuration and electronic distribution, leading to the weakening of molecular aromaticity, and this transformation may even result in the anti-aromaticity of the system. In this study, taking porphyrazine as the object, we used the classical aromaticity descriptors to discuss the main conjugation pathways and compare aromaticity in terms of magnetic property, geometric structure and electronic delocalization upon the deprotonation/protonation and dehydrogenation/hydrogenation. The molecular UV–vis spectra were simulated theoretically, and the frontier orbitals excitation characteristics were analyzed to identify the aromaticity modulation effect. It is found that the aromaticity of porphyrazine is modulated with the number of H or H + regulations in the molecular structure, the photophysical properties of each molecule change significantly.