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

A new family of unsymmetrically mixed β-octasubstituted porphyrins, H2TPP(Ph)3X5 (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 < Cl < Br. The crystal structures of the NiTPP(Ph)3X5 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) Å; CH3, 0.700(2) Å). Similarly, the structure of CuTPP(Ph)3(CH3)5 showed an enhanced distortion (r.m.s. = 0.599(4) Å) 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.

A new class of unsymmetrically mixed β-octasubstituted meso-tetraphenylporphyrins has been reported. These porphyrins reveal a significant red-shift in the electronic absorption spectral bands and an interesting trend in the electrochemical redox properties. The crystal structures of the Ni(II) and Cu(II) complexes of unsymmetrically substituted porphyrins showed notable differences in the out-of-plane distortion of the non-planar macrocycle.Figure optionsDownload as PowerPoint slide