Electronic structure and theoretical modeling of UV-Vis-NIR spectra of ferrocene containing tetrazaporphyrins

Abstract

The UV-Vis-NIR spectra of two ferrocene substituted tetraazaporphyrins were analyzed by use of time dependent density functional theory (TDDFT) and polarized continuum model TDDFT (PCM-TDDFT) methods. The TDDFT and PCM-TDDFT calculations were done using four different exchange-correlation functionals (BPW91, BP86, B3LYP, PBE1PBE) with varying amounts of Hartree-Fock exchange included in the functional to find the best agreement between theory and experiment. Once the best agreement was found by comparing experimental spectrum to the PCM-TDDFT calculations, using the B3LYP functional, further calculations were carried out with this functional to assign the electronic transitions that made up the UV-Vis-NIR spectrum and generate the contours of the corresponding molecular orbitals involved. Once assigned, transitions toward the near-IR end of the spectrum (Identified by Region 1; see Figure 12) were found to be predominately metal-to-ligand charge transfer transitions (MLCT) between the iron atoms of the ferrocene substituents and the π* system of the tetraazaporphyrin ring. Transitions toward the UV end of the spectrum (Identified by Region 4; see Figure 12) were found to be predominately π→π* transitions of the tetraazaporphyrin ring. If was also found that the major transitions are fairly mixed in character due to mixed nature of the molecular orbitals involved, containing varying percentages of both tetraazaporphyrin and ferrocene character.