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

Abstract

Utilization 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.

New Insight into an Old Problem: Analysis, Interpretation, and Theoretical Modeling of the Absorption and Magnetic Circular Dichroism Spectra of Monomeric and Dimeric Zinc Phthalocyanine Cation Radical

“…Such a transition can be observed both in solution and in the solid state. Formation and understanding of the spectroscopic signatures of the phthalocyanine-centered cation radicals are also important when electron transfer, and specifically formation of the charge-separated states, in the phthalocyanine-containing supramolecular systems are needed for solar cell applications. − Typically, upon oxidation of main group and transition-metal phthalocyanines to their respective cation radical forms, both the monomeric cation radical [MPc] +• and the dimeric [MPc] 2 2+ species (M is a divalent metal) can be formed in solution . The monomeric cation radical is paramagnetic and can be easily identified by electron paramagnetic resonance (EPR) spectroscopy (classic signal observed at g ≈ 2, which is characteristic for delocalized organic radical cations) .…”

Fullerene as Spin Converter

“…For their possible application in photodynamic therapy, a prototype macromolecule bearing a distyrylbenzene dimer as TPA unit and a [60] fullerene moiety for singlet oxygen generation endowed with a high two-photon absorption (TPA) cross section and a high singlet oxygen quantum yield were reported by Collini et al (Figure 5) [105]. The singlet oxygen generation and photoinduced charge separation of zinc phthalocyaninefullerene dyad bearing tetra polyethylene glycol moieties were also reported for PDT application [106].…”