title: Generation Dependent Ultrafast Charge Separation and Recombination in a Pyrene-Viologen Family of Dendrons.
abstract: The ability of a dendritic network to intercept electrons and extend the lifetime of a short-lived photoinduced charge separated (CS) state was investigated in a homologous family of methyl viologen (MV(2+)) dendrons spanning four generations, G0 through G3. The CS state in the parent pyrene-methylene-viologen G0 system with a single acceptor exhibits an extremely short lifetime of τ = 0.72 ps. The expansion of the viologen network introduces slower components to the recombination kinetics by allowing the injected electron to migrate further away from the donor. The long-lived fraction of the population increases monotonically in the order G3 > G2 > G1 > G0, while the respective recombination rates decrease. In the highest generation of the dendron ∼14% of the CS state population experiences a 10-fold or greater lifetime extension. Long range tunneling across multiple viologen units and sequential site-to-site hopping both contribute to the overall effect. The large excess energy deposited in the apical viologen upon charge separation and the presence of an extended network of low lying π-orbitals likely facilitate shuttling the electron further down the dendron.
authors.affiliation: Department of Chemistry, Rutgers University , 73 Warren Street, Newark, New Jersey 07102, United States.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Gong
authors.affiliation: Department of Chemistry, Rutgers University , 73 Warren Street, Newark, New Jersey 07102, United States.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Bao
authors.affiliation: Iyoda Supra-Integrated Material Project, Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency (JST), and Frontier Research Center, Tokyo Institute of Technology , 4259-S2-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Keiji
authors.initials: K
authors.lastname: Nagai
authors.affiliation: Iyoda Supra-Integrated Material Project, Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency (JST), and Frontier Research Center, Tokyo Institute of Technology , 4259-S2-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Iyoda
authors.affiliation: Iyoda Supra-Integrated Material Project, Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency (JST), and Frontier Research Center, Tokyo Institute of Technology , 4259-S2-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Takehiro
authors.initials: T
authors.lastname: Kawauchi
authors.affiliation: Department of Chemistry, Rutgers University , 73 Warren Street, Newark, New Jersey 07102, United States.|Institute of Advanced Materials, Devices and Nanotechnology, Rutgers University , 607 Taylor Road, Piscataway, New Jersey 08854, United States.
authors.forename: Piotr
authors.initials: P
authors.lastname: Piotrowiak