Synthesis, spectroscopic and electrochemical investigation on the conformational features of meso-5-formylthien-2-ylporphyrins and its terpyridinylthien-2-ylporphyrin and Porphyrin-Corrole dyad

A facile approach for the syntheses of regioselective meso- mono, di (cis and trans), and tri formylthien-2-ylporphyrins from meso-tetrathien-2-ylporphyrin (ThP) is presented. The synthesized meso- mono formylthien-2-ylporphyrin ThP-CHO was further functionalized to 5-((5-terpyridinyl)thien-2-yl)-10,15,20-tris(thien-2-yl)porphyrin (ThP-TPy) and Porphyrin-Corrole (Por-Cor) dyad. The influence of formyl substitution and further functionalization on meso- thien-2-yl ring(s) with porphyrin central pi-system is examined through UV-Vis absorption, H-1 NMR spectroscopy and electrochemical studies. The red shift of Soret band and Q bands in the absorption spectrum and the redox potentials are shown to be dependent on the number of substitution (ThP-CHO, 424 nm < ThPt-(CHO)(2) and ThPc-(CHO)(2), 425 nm < ThP(CHO)(3), 427 nm). The significant variation in redox potentials and distinct bathochromic shift in the absorption bands in the series of formyl derivatives, ThP-TPy and Por-Cor dyad have been explained based on the near-planar orientation of the meso-thienyl groups with the porphyrin core.