A Density Functional Study of the Redox Properties of H2TPP Porphyrin*

Properties of the ground state of free base meso-tetraphenylporphyrin (H2TPP) have been calculated with various charges using the B3LYP functional and the 6-31$+$G basis set. The porphyrin skeleton was rippled and saddled and the meso-phenyl rings were twisted to yield the C$_{\mathrm{2h}}$, C$_{\mathrm{2v}}$, D$_{2}$, D$_{\mathrm{2h}}$ planar and D$_{\mathrm{2h}}$ non-planar symmetries and the structures optimized. The ground state structure was found to be of C$_{\mathrm{2v}}$ symmetry although the C$_{\mathrm{2h}}$, D$_{\mathrm{2}}$ and D$_{\mathrm{2h}}$ non-planar structures were basically degenerate, a conclusion not supported by experimental data. The C$_{\mathrm{2v}}$ structure indicated a nonzero net dipole moment for all levels of charge studied. Increase in negative charge increased the distortion of the H2TPP structure. The Raman spectra was calculated and compared with experimental data.\footnote{J.E. Parker, R. J. Thomas, D. R. Morrison, L. Brancaleon, \textit{J. Phys. Chem. B}, 2012, 116 (36), pp 11032--11040.} In addition, the results were used to select the most likely binding configuration among a set of solutions yielded by computational docking algorithms. Calculations using higher basis sets will also be presented.