Singlet Oxygen Generation and Photoinduced Charge Separation of Tetra Polyethyleneglycol Functionalized Zinc Phthalocyanine‐Fullerene Dyad

Abstract

AbstractUtilization of polyethyleneglycol (PEG) functionalized zinc phthalocyanine, (PEG)4ZnPc in (i) singlet oxygen generation, and (ii) in building energy harvesting donor‐acceptor systems using fullerene, C60 as an acceptor via the well‐known metal‐ligand axial coordination approach is reported. The (PEG)4ZnPc was found to be capable of producing singlet oxygen with a quantum yield, ΦΔ of 0.77 in toluene, a value higher than that obtained for pristine (t‐bu)4ZnPc (ΦΔ=0.54) carrying no PEG groups, revealing its usefulness in photodynamic therapy applications. Spectroscopic studies revealed efficient binding of phenylimidazole functionalized fullerene, C60Im with 1:1 stoichiometry to (PEG)4ZnPc. Binding constant K for the formation of (PEG)4ZnPc:ImC60 dyad was found to be 6×103 M−1 revealing moderate stability. Geometric and electronic studies of the dyad was arrived by B3LYP/3‐21G(∗︁) method. The HOMO level was found to be on zinc phthalocyanine entity while the LUMO level was found to be on the C60 entity suggesting formation of (PEG)4ZnPc·+:ImC60· − charge separated state during the process of electron transfer reaction. Redox studies on the (PEG)4ZnPc:ImC60 dyad enabled accurate determination of the oxidation and reduction potentials of the donor‐acceptor system, and to evaluate free‐energy changes associated for the charge separation process. Kinetics of photoinduced charge separation and recombination in the (PEG)4ZnPc:ImC60 dyad was investigated using femtosecond transient absorption studies. Relatively long‐lived charge separated states were confirmed for the dyad suggesting their potential usefulness in energy harvesting applications.