Unsymmetrically mixed β-octasubstituted meso-tetraphenylporphyrins: Structural and electrochemical redox properties

A new family of unsymmetrically mixed beta-octasubstituted porphyrins, H2TPP(Ph)(3)X-5 (X = H, Cl, Br and CH3), and their metal complexes were synthesized. These porphyrins feature red-shifted electronic absorption bands, depending on the nature of the 'X' group and following the trend: H < CH3 < CI < Br. The crystal structures of the NiTPP(Ph)(3)X-5 complexes reveal an enhanced distortion of the macrocycle, as evidenced from root-mean square (r.m.s.) values, and it varies with the size of X (H. 0.407(2) angstrom; CH3, 0.700(2) angstrom). Similarly, the structure of CuTPP(Ph)(3)(CH3)(5) showed an enhanced distortion (r.m.s. = 0.599(4) angstrom) of the macrocycle. Normal-coordinate structure decomposition analysis of the crystal structures revealed mainly saddling (40-78%) and ruffling (15-51%) deformations. The electrochemical properties of these derivatives generally exhibited an anodic shift of the redox potentials and the HOMO-LUMO gap determined from the redox data correlates reasonably well with the longest wavelength absorption spectral data. (C) 2014 Elsevier Ltd. All rights reserved.