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

Abstract Utilization of polyethyleneglycol (PEG) functionalized zinc phthalocyanine, (PEG) 4 ZnPc in (i) singlet oxygen generation, and (ii) in building energy harvesting donor‐acceptor systems using fullerene, C 60 as an acceptor via the well‐known metal‐ligand axial coordination approach is reported. The (PEG) 4 ZnPc was found to be capable of producing singlet oxygen with a quantum yield, Φ Δ of 0.77 in toluene, a value higher than that obtained for pristine ( t ‐bu) 4 ZnPc ( Φ Δ =0.54) carrying no PEG groups, revealing its usefulness in photodynamic therapy applications. Spectroscopic studies revealed efficient binding of phenylimidazole functionalized fullerene, C 60 Im with 1:1 stoichiometry to (PEG) 4 ZnPc. Binding constant K for the formation of (PEG) 4 ZnPc:ImC 60 dyad was found to be 6×10 3 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 C 60 entity suggesting formation of (PEG) 4 ZnPc ·+ :ImC 60 · − charge separated state during the process of electron transfer reaction. Redox studies on the (PEG) 4 ZnPc:ImC 60 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) 4 ZnPc:ImC 60 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.