Mixed β-pyrrole substituted meso-tetraphenylporphyrins and their metal complexes: Synthesis, structures and electrochemical redox properties

• This work reports the synthesis of two new classes of mixed β-octasubstituted MTPPs.
• Porphyrins displayed interesting optical absorption, redox and structural properties.
• X-ray structural analysis of some derivatives showed mainly saddled macrocycle.
• Free base porphyrins showed tunable optical absorption spectral properties.

Synthesis of two new classes of mixed β-pyrrole substituted tetraphenylporphyrins, H2TPP(Ph)4(R)4 (R = 2-thienyl and phenylethynyl, PE) and H2TPP(CH3)4(R)4 (R = 2-thienyl and PE) and their metal complexes have been reported. These porphyrins showed dramatic red-shift in electronic absorption bands relative to their corresponding MTPP(R)4 derivatives. Crystal structures of H2TPP(R)4(2-thienyl)4 (R = Ph and CH3) and MTPP(CH3)4(PE)4 (M = Zn(II) and Cu(II)) derivatives are highly nonplanar as evidenced from the mean displacement of β-pyrrole carbon (ΔCb) in the range ±(0.33–1.07) Å. Normal-coordinate structural decomposition analysis of the 24-atom core in these crystal structures revealed largely saddle (73–93%) combined with different degree of ruffled, domed and wave distortions. Electrochemical redox properties of these porphyrins exhibited interesting trend in redox potentials relative to their corresponding H2TPP(R)4s. The tunable trend in redox potentials and electronic absorption bands of mixed substituted porphyrins suggests the role of nonplanarity of macrocycle and electronic effects of the substituents.

This article reports the synthesis of two new classes of mixed β-octasubstituted porphyrins, H2TPP(R)4(X)4 (R = Ph/CH3 and X = phenylethynyl (PE), 2-thienyl) and their metal (Co(II), Cu(II) and Zn(II)) complexes. Crystal structures of mixed substituted porphyrins revealed mainly saddle distortion of the macrocycle. These free base porphyrins exhibited tunable absorption and electrochemical redox properties.Figure optionsDownload as PowerPoint slide