Covalently linked diphenylethyne bridged meso-aryl 22-oxabenzonorrole–porphyrin/metalloporphyrin dyads

Abstract

The first example of covalently linked, diphenyl ethyne-bridged 22-oxabenzonorrole–Zn(II) porphyrin dyad 7 was synthesized by Sonogashira cross-coupling of newly synthesized 10,15-bis(p-tolyl)-5-(p-iodophenyl) 22-oxabenzonorrole 6 with 5-[4-ethynylphenyl]-10,15,20-tri(p-tolyl) porphyrin 14 in toluene/TEA at 45 °C for 12 h. The diphenyl ethyne bridged 22-oxabenzonorrole–porphyrin dyad 8 was obtained by treating dyad 7 with trifluoroacetic acid (TFA) in CH₂Cl₂ at room temperature, whereas the 22-oxabenzonorrole–Cu(II) porphyrin dyad 9 was synthesized by reacting dyad 8 with Cu(CH₃COO)₂ in CHCl₃/CH₃OH under reflux. The synthesized dyads 7–9 contain two different subunits, namely a less aromatic 22-oxabenzonorrole macrocycle having a novel N–C linkage in its macrocyclic framework and a highly aromatic 18π porphyrin with different physicochemical properties. The absorption and electrochemical studies revealed that the dyads 7–9 exhibit the characteristic features of both the constituted macrocycles and indicated a weak interaction between the subunits. The DFT studies revealed that in dyads 7–9, both subunits were oriented with a dihedral angle in the range of 77–81° with respect to each other.