title: Intramolecular electron and energy transfer in an axial ZnP-pyridylfullerene complex as studied by X- and W-band time-resolved EPR spectroscopy.
abstract: Light-driven electron transfer (ET) and energy transfer (EnT) in a self-assembled via axial coordination Zn-porphyrin-pyridylfullerene (ZnP-PyrF) complex were studied by time-resolved electron paramagnetic resonance (TREPR) spectroscopy at 9.5 GHz (X-band) and 95 GHz (W-band). The studies over a wide temperature range were carried out in media of different polarity, including isotropic toluene and tetrahydrofuran (THF), and anisotropic nematic liquid crystals (LCs), E-7 and ZLI-4389. At low temperatures (frozen matrices), photoexcitation of the ZnP donor results mainly in singlet-singlet EnT to the pyridine-appended fullerene acceptor. In fluid phases ET is the dominant process. Specifically, in isotropic solvents the generated radical pairs (RPs) are long-lived, with lifetimes exceeding that observed for covalently linked donor-acceptor systems. It is concluded that in liquid phases of both polar and nonpolar solvents the separation of the tightly bound complex into the more loosely bound structure slows down the back ET (BET) process. Photoexcitation of the donor in fluid phases of LCs does not result in the creation of the long-lived RPs, since the ordered LC matrix hinders the separation of the complex constituents. As a result, fast intramolecular BET takes place in the tightly bound complex. Contrarily to the behavior of covalently linked donor-acceptor systems in different LCs, the polarity of the LC matrix affects the ET process. Moreover, in contrast to covalently linked D-s-A systems, utilization of LCs for the coordinatively linked D-s-A complexes does not reduce the ET rates significantly.
authors.affiliation: Department of Physical Chemistry and the Farkas Center for Light-Induced Processes, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Tamar
authors.initials: T
authors.lastname: Galili
authors.forename: Ayelet
authors.initials: A
authors.lastname: Regev
authors.forename: Alexander
authors.initials: A
authors.lastname: Berg
authors.forename: Haim
authors.initials: H
authors.lastname: Levanon
authors.forename: David I
authors.initials: DI
authors.lastname: Schuster
authors.forename: Klaus
authors.initials: K
authors.lastname: Möbius
authors.forename: Anton
authors.initials: A
authors.lastname: Savitsky
mesh_terms: D016880:Anisotropy; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004583:Electrons; D004735:Energy Transfer; D037741:Fullerenes / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010777:Photochemistry; D011166:Porphyrins / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013696:Temperature; D013997:Time Factors; D015032:Zinc / Q000737:chemistry*
chemical_list: D037741:Fullerenes; D009942:Organometallic Compounds; D011166:Porphyrins; D015032:Zinc