β‐Trisubstituted “Push–Pull” Porphyrins – Synthesis and Structural, Photophysical, and Electrochemical Redox Properties

Abstract

A family of tri‐β‐substituted porphyrins, MTPP(CH3)2X (M = 2H, Co, Ni, Cu and Zn; X = NO2 or CHO; TPP = tetraphenylporphyrin), was synthesized and characterized by various spectroscopic techniques. The single‐crystal X‐ray structures of NiTPP(CH3)2CHO and H2TPP(CH3)2NO2 revealed ruffled and saddle conformations of the porphyrin core, respectively. The effects of the β substituents were reflected in bathochromic shifts of the electronic spectral features and positive or negative shifts of the redox potentials. H2TPP(CH3)2NO2 and H2TPP(CH3)2CHO exhibited very high dipole moments (5.76–7.59 D) compared with that of H2TPP (0.052 D) owing to the push–pull effect. These push–pull porphyrins exhibited lower HOMO–LUMO gaps than those of MTPP(NO2) and MTPP. The redox tunability was achieved through the introduction of electron donor and acceptor groups at the porphyrin backbone.