Structures and spectroscopic properties of fluoroboron-subtriazaporphyrin derivatives: density functional theory approach on the benzo-fusing effect

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were carried out to comparatively study the molecular structures, atomic charges, molecular orbitals, and electronic absorption spectra of fluoroboron-subtriazaporphyrin (SubTAP) and fluoroboron-subphthalocyanine (SubPc) as well as their benzo-fused low-symmetrical derivatives A_aB_bC_c (3 > a, b, c > 0). The peripherally fused benzene rings are revealed to have a significant effect on the structure and charge density distribution of the inner nitrogen atoms of subtriazaporphyrin core, while the charge of the central fluoroboron group changes very little. The effect of peripherally fused benzene rings on the frontier molecular orbitais of different compounds is comparatively discussed. The nature of the electron excitation between the frontier molecular orbitais of the 20 compounds is assigned according to the calculation results. The benzene rings fused directly onto pyrrole rings have been revealed to show more effect on the inner nitrogen atom than the outer benzene rings fused onto the periphery of isoindole rings. The present work will be helpful toward systematically understanding the effect of ring enlargement through asymmetrically fusing benzene ring(s) onto the subtriazaporphyrin skeleton on the structures and properties of fluoroboron-subtriazaporphyrin and fluoroboron - subphthalocyanine analogues.