title: Complete Monitoring of Coherent and Incoherent Spin Flip Domains in the Recombination of Charge-Separated States of Donor-Iridium Complex-Acceptor Triads.
abstract: The spin chemistry of photoinduced charge-separated (CS) states of three triads comprising one or two triarylamine donors, a cyclometalated iridium complex sensitizer and a naphthalene diimide (NDI) acceptor, was investigated by transient absorption spectroscopy in the ns-μs time regime. Strong magnetic-field effects (MFE) were observed for two triads with a phenylene bridge between iridium complex sensitizer and NDI acceptor. For these triads, the lifetimes of the CS states increased from 0.6 μs at zero field to 40 μs at about 2 T. Substituting the phenylene by a biphenyl bridge causes the lifetime of the CS state at zero field to increase by more than 2 orders of magnitude (τ = 79 μs) and the MFE to disappear almost completely. The kinetic MFE was analyzed in the framework of a generalized Hayashi-Nagakura scheme describing coherent (S, T0 ↔ T±) as well as incoherent (S, T0 ⇌ T±) processes by a single rate constant k±. The magnetic-field dependence of k± of the triads with phenylene bridge spans 2 orders of magnitude and exhibits a biphasic behavior characterized by a superposition of two Lorentzians. This biphasic MFE is observed for the first time and is clearly attributable to the coherent (B < 10 mT) and incoherent (10 mT < B < 2 T) domains of spin motion induced by isotropic and anisotropic hyperfine coupling. The parameters of both domains are well understood in terms of the structural properties of the two triads, including the effect of electron hopping in the triad with two donor moieties. The kinetic model also accounts for the reduction of the MFE on reducing the rate constant of charge recombination in the triad with the biphenyl bridge.
authors.affiliation: Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Würzburg, Center for Nanosystems Chemistry, Institut für Organische Chemie, Universität Würzburg , Am Hubland, 97074 Würzburg, Germany.
authors.forename: Johannes H
authors.initials: JH
authors.lastname: Klein
authors.affiliation: Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Würzburg, Center for Nanosystems Chemistry, Institut für Organische Chemie, Universität Würzburg , Am Hubland, 97074 Würzburg, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Schmidt
authors.affiliation: Fachbereich Chemie, Universität Konstanz 78457 Konstanz, Germany.
authors.forename: Ulrich E
authors.initials: UE
authors.lastname: Steiner
authors.affiliation: Wilhelm Conrad Röntgen Research Center for Complex Material Systems, Würzburg, Center for Nanosystems Chemistry, Institut für Organische Chemie, Universität Würzburg , Am Hubland, 97074 Würzburg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Lambert
mesh_terms: D000588:Amines / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007094:Imides / Q000737:chemistry*; D007495:Iridium / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*
chemical_list: D000588:Amines; D007094:Imides; D009281:Naphthalenes; D009942:Organometallic Compounds; C542131:naphthalenediimide; D007495:Iridium