Theoretical investigations on electronic structures and absorption spectra of unsymmetrical metal-coordinated neo-confused porphyrin in various solvents

Though the photo-physical properties of free base porphyrin are attractive, there are still problems for the materials with weak and narrow range absorption of visible light. The unsymmetrical neo-confused porphyrin derivatives were introduced as novel materials for the improvement of photo-chemical and photo-physical properties. The density function theory (DFT) and time dependent density function theory (TDDFT) were applied to calculate the absorption spectrum of unsymmetrical neo-confused porphyrin (N-CP) and metal-coordinated N-CP in various solutions. The Ni and Zn coordinated neo-confused porphyrin dipole moment values are smaller than the values of prototype porphyrin (ProP) and N-CP. According to the electrophilicity index ω, Ni coordinated N-CP (Ni-N-CP) is susceptible to the polarity of solvents, while the Zn coordinated derivative (Zn-N-CP) is more immune to the solvent environment. Unlike the Gouterman's four frontier orbital model of common porphyrin materials, the electron transitions of N-CPs and metal-coordinated N-CPs from H-2 or lower molecular orbitals also contribute to ultraviolet and visible absorption. Most of oscillator strength f values of Zn-N-CP are significantly higher than the values of Ni-N-CP, which reflects the higher absorption intensity of Q and Soret bands. The maximum wavelength at 702.2 nm in vacuum drew our attention to the novel material. The broad absorption range, intense red-shifted Q band and higher stability in solvents suggest that N-CPs, especially Zn-N-CP, can be one class of new candidate dye-sensitized materials.