The electronic properties of di-axially substituted metal phthalocyanine complexes have previously been studied experimentally through UV-Vis spectroscopy and magnetic circular dichroism (MCD) spectroscopy. The dominant features of the UV-Vis spectra are a Q-band located above 600 nm, a B-band located below 400 nm and a ligand-dependent band between the Q-band and the B-band. The MCD spectra contain an A-term corresponding to the Q-band, along with multiple A-terms and B-terms corresponding to the transitions comprising the B-band and the ligand-dependent band. One component of the ligand-dependent band is metal to ligand charge transfer (MLCT) transitions between the metal center and the phthalocyanine ring. The first MCD A-term after the Q-band has always been assigned as the MLCT transitions. Theoretical methods have been used to predict the UV-Vis and MCD spectra of metal phthalocyanine complexes. However, the predicted MLCT wavelengths have always been inaccurate compared to the experimental wavelengths. Moreover, a linear correlation between the experimental MLCT wavelengths and the relative strengths of the σ-donating and π-accepting properties of the axial ligands was expected but not seen. It was hypothesized that the assignment of the MLCT transitions to the first A-term after the Q-band may have been incorrect, while the theoretically predicted MLCT wavelengths may have been accurate. One of the goals of the study was to test this hypothesis. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were done in Gaussian 16, with three different functionals containing different amounts of Hartree-Fock exchange, as this has been found to be an important consideration for spectral predictions. Two different solvents were used to correspond to the experimental side of the study.

Metal to ligand charge transfer in iron phthalocyanine complexes

ACS Spring Meeting 2021

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