β-Heptasubstituted Porphyrins: Synthesis, Structural, Spectral, and Electrochemical Properties

Abstract

A new series of β-heptasubstituted porphyrins MTPP(NO2)(Me)6 (M = 2H, CoII, NiII, CuII, and ZnII) was synthesized and characterized by various spectroscopic techniques. The single-crystal X-ray structure analysis of CoTPP(NO2)(Me)6 revealed the significant saddle distortion of the macrocyclic core from the porphyrin mean plane (ΔCβ = 0.928 Å). These porphyrins exhibit significant redshifted electronic spectral features (Δλmax = 40–62 nm) as compared with MTPP due to the combined effect of the nonplanar conformation of the macrocyclic core and mixed β-substituents. H2TPP(NO2)(Me)6 has shown a high dipole moment (7.12 D) as compared with H2TPP (0.052 D) due to cross-polarized push–pull substituents. The redox tunability was achieved by appending the electron-donating methyl and electron-withdrawing NO2 group at the β-positions of the porphyrin skeleton.