Polyoligopeptides functionalized zinc(II)porphyrins: Step towards artificial hemes

Two new zinc(II)porphyrin oligopeptide conjugates (zinc(II)-5,10,15,20-bis[4-(peptide)- phenyl]porphyrin (5) and -tetrakis[3,5-di(peptide)phenyl]porphyrin (9; peptide = -CH 2 (CO)Gly-Phe-Ala-CNH 2 ) were prepared using the click chemistry with azides and ethynyl-containing precursors. The spectroscopic signature (S 0 →S 1 and transient T 1 →T n absorption, excitation and emission spectra) are typical for zinc(II)porphyrin and shows no perturbation upon anchoring the oligopeptides, whereas some small decreases in the photophysical parameters (𝜏 F and Φ F ), and larger decrease in T 1 lifetimes are noted, which are attributable to the known "loose bolt" effect. The structure for 9 in solution was addressed qualitatively using computer modeling and the comparison of the bimolecular fluorescence quenching rate constants between 5 and 9 using C 60 as a photooxidative agent. While 5 exhibits a totally accessible zinc(II)porphyrin unit for a C 60 approach, 9 shows a slower quenching rate constant meaning some steric hindrance must be present.