Structural, photophysical, and electrochemical redox properties of meso-tetrakis(pentafluorophenyl)porphyrins

Abstract

This study delineates the synthesis and comprehensive characterization of metal complexes of meso-tetrakis(pentafluorophenyl)porphyrin (H₂TPF${}_{20}$P, 1) with first-row transition metal ions (M = Mn(III) 2, Fe(III) 3, Co(II) 4, Ni(II) 5, Cu(II) 6, and Zn(II) 7) to elucidate their structural, electronic spectral, and electrochemical redox properties. Co, Ni, Cu and Zn Complexes exhibit planar structure ($\mathrm{\Delta }$24 = 0.003-0.021 Å and $\mathrm{\Delta }$C${}_{\beta }$ = 0.004−0.041 Å) which is also confirmed by the single crystal data of complex ZnTPF${}_{20}$P, 7 shows the planar geometry, while Fe and Mn complexes show the slightly nonplanar structure ($\mathrm{\Delta }$24 = 0.101–0.143 Å and $\mathrm{\Delta }$C${}_{\beta }$ = 0.080–0.112 Å), which are distorted due to their occupied axial sites by −Cl ligand as revealed by density functional theory (DFT) calculations. Furthermore, electronic spectroscopy revealed a gradual bathochromic shift following the order of NiTPF${}_{20}$P < CoTPF${}_{20}$P < CuTPF${}_{20}$PCl < H₂TPF${}_{20}$P = FeTPF${}_{20}$PCl < ZnTPF${}_{20}$P < MnTPF${}_{20}$PCl by appending different metal ions in the porphyrin core. MnTPF${}_{20}$PCl exhibited the most significant bathochromic shift ($\mathrm{\Delta }{\lambda }_{\text{max}}$ = 63 nm) in the Soret band compared to H₂TPF${}_{20}$P. Also, MnTPF${}_{20}$PCl and FeTPF${}_{20}$PCl show a unique pattern of split Soret band at around 364 and 345 nm due to the interaction between the metal $d$-orbitals and the surrounding ligands. The electrochemical redox potentials of the filled 3d orbital of Zn endow ZnTPF${}_{20}$P (ring centered) with the lowest oxidation potential.