Theoretical study on the geometry, aromaticity and electronic properties of porphyrin analogues

Density functional theory calculations were employed to investigate a family of porphyrin analogues differing in macrocyclic size and bridging motif. The geometrical features of these macrocycles exhibit pronounced variations in bond lengths, bond angles, and overall conformations as the framework size and linkage patterns are altered. Nucleus independent chemical shift (NICS) values and anisotropy of the induced current density (AICD) analyses were calculated to evaluate the aromaticity of the porphyrin analogues. The porphyrin analogues exhibit pronounced aromatic character. The electronic properties were further examined by frontier molecular orbital analysis, revealing systematic changes in orbital energies with increasing π-conjugation length and with nitrogen substitution at the meso positions. We expect that these studies will provide new insights and will aid the further development of diverse novel porphyrin analogues.