Porphyrins. 40. Electronic spectra and four-orbital energies of free-base, zinc, copper, and palladium tetrakis(perfluorophenyl)porphyrins

Article abstract of DOI:10.1021/ic50204a021

Absorption and emission spectra and emission quantum yields are given for free-base (H₂), Zn, Cu, and Pd derivatives of tetrakis(perfluorophenyl)porphyrin (TFPP). The four-orbital model is used to rationalize differences in the optical properties among the derivatives of TFPP and the same derivatives of porphine (P), octaethylporphyrin (OEP), and tetraphenylporphyrin (TPP). It is concluded from absorption data that the energy difference between the two excited singlets, i.e., ¹E(a_2u,e_g) -¹E(a_1u,e_g), decreases along the series Pd > Cu > Zn > H₂ and also along the series OEP > P ? TFPP > TPP. The theory and date are reviewed, and it is concluded that the energy difference between the two excited triplets, i.e., ³E(a_2u,e_g) -³E(a_1u,e_g), also decreases along these series. However the condition of degeneracy, e.g., ¹E(a_2u,e_g) - ¹E(a_1u,e_g) = 0, occurs for different molecules in the singlet and triplet cases. Theory also suggests that if ³E(a_2u,e_g) > ³E(a_1u,e_g), the molecule should form a ²A_1u cation radical and if ³E(a_2u,e_g) < ³E(a_1u,e_g) the molecule should form a ²A_2u radical.