Structural and photophysical studies of trans-AB2C-substituted porphyrinligands and their zinc and copper complexes

Abstract

trans-AB₂C porphyrins with A = C₆H₄–COOR, C = C₆H₄–NX₂ and B = C₆H₅ (R = CH₃, H; X = O, H) have been synthesised by a rational high-yield procedure (1a–1d) and their zinc(II) and copper(II) complexes have been prepared (2a–2d, 3a–3d). 1a, 2a·THF and 3a display different distortions of the porphyrin core as shown by single crystal X-ray crystallography and NSD analyses. The Soret and Q bands of free-base and metalated porphyrins with mixed electron donating and withdrawing substituents (NH₂/COOR) are red-shifted as are the corresponding emission bands of free-base and zinc porphyrins. The electronic asymmetry revealed by spectrocopy is rationalised by DFT calculations.