Meso-tetrathienylporphyrins: electrochemical and axial ligation properties

5,10,15,20-Tetrakis(2′- and 3′-thienyl)porphyrins [H2T(2′-Thio)P and H2T(3′-Thio)P] and their metal [Zn(II) and Cu(II)] complexes were examined by electrochemical redox and axial ligation properties. A large anodic shift (100–150 mV) in reduction potentials was observed for MT(2′-Thio)Ps relative to MTPPs or MT(3′-Thio)Ps. MT(2′-Thio)Ps exhibited unusual redox behaviour and follows the trend in oxidation; CuT(2′-Thio)P>H2T(2′-Thio)P⩾ZnT(2′-Thio)P in contrast to their corresponding MTPPs, H2TPP>CuTPP>ZnTPP. It is reflected in the enhanced equilibrium constants (>60%) for the ligation of nitrogenous bases with ZnT(2′-Thio)P when compared to ZnTPP. This is interpreted in terms of increased electron deficient nature of the ZnT(2′-Thio)P in contrast to Zn(3′-Thio)P or ZnTPP.