New Materials Design. Free-base Porphyrin and Its Meso-tetrahalogenated Derivatives

Ab initio electronic structure theory has been applied to predict the structures and electronic spectra of free-base porphyrin (PH2) and its meso-tetrahalogenated derivatives (m-PX8H2; X = F, Cl, Br). Structures, singlet-triplet energy gaps, and electronic spectra are predicted using the B3LYP method in conjunction with the 6-31G(d) basis set and the effective core potentials/basis sets of Stevens et al. Minimum energy structures of the lowest triplet excited states (Τ1) were found to retain D2h symmetry with stretched Cβ-Cβ and Cβ-Cm bond distances. We found that halogenation at the four meso-positions significantly changes the ground state excitation energies and the singlet-triplet gap for the free-base parent compound.