New synthesis of zinc tetrakis(arylethynyl) porphyrins and substituent effects on their redox chemistry

摘要

Sonogashira coupling of zinc 5,10,15,20-tetraethynylporphyrin with various phenyl iodides under mild conditions afforded good yields of the corresponding zinc porphyrins. This method is applicable to a variety of aryl iodides including meso-substituted iodoporphyrin to form a conjugated star-shaped multiporphyrin. The UV-Vis spectra show that peak broadening, red shifts, and changes in the oscillator strength of absorptions increase with the extension of pi-conjugation. In the electrochemical measurements, the first oxidation of porphyrins 4-9 occurs at potentials in the range + 0.89 to + 1.08 V, which are comparable to that of ZnTPP (TPP = tetraphenylporphyrin). The first reduction was observed at potentials from -0.73 to - 0.89 V, which is anodically shifted by 390-550 mV as compared to that of ZnTPP, and the second reduction occurs at potentials in the range -1.12 to -1.33 V. The para-substituted tetrakis(phenylethynyl) porphyrins show substituent effects on their redox chemistry and exhibit only slight substituent effects in their emission and absorption maxima.