Comparative electronic structures and UV-vis spectra of tribenzosubporphyrin, tribenzomonoazasubporphyrin, tribenzodiazasubporphyrin, and subphthalocyanine: Insight from DFT and TDDFT calculations

Electronic structures, geometries, and vertical excitation energies of chloroboron subphthalocyanine, tribenzodiazasubporphyrin, tribenzomonoazasubporphyrin, and tribenzosubporphyrin were calculated using density functional theory (DFT) and time-dependent (TD) DFT coupled with polarized continuum model (PCM) approach. Molecular geometries calculated at the BP86/6-311G(d) level reveal bowl-shape, trigonal prismatic conformations for all compounds with a variable bowl-depth that depends on the number of meso-nitrogen atoms in corresponding molecule. TDDFT-PCM calculations predict that the Q-band should undergo gradual high-energy shift, while the B-band should undergo low-energy shift upon stepwise substitution of the meso-nitrogen atoms in subphthalocyanine toward tribenzosubporphyrin. The TDDFT-PCM predicted trend was rationalized on the basis of electronic structures of target macrocycles. When comparison between theory and experiment is available, TDDFT-PCM calculations are in qualitative and quantitative agreement with experimental data.