title: Operative Mechanism of Hole-Assisted Negative Charge Motion in Ground States of Radical-Anion Molecular Wires.
abstract: Charge transfer/transport in molecular wires over varying distances is a subject of great interest. The feasible transport mechanisms have been generally accounted for on the basis of tunneling or superexchange charge transfer operating over small distances which progressively gives way to hopping transport over larger distances. The underlying molecular sequential steps that likely take place during hopping and the operative mechanism occurring at intermediate distances have received much less attention given the difficulty in assessing detailed molecular-level information. We describe here the operating mechanisms for unimolecular electron transfer/transport in the ground state of radical-anion mixed-valence derivatives occurring between their terminal perchlorotriphenylmethyl/ide groups through thiophene-vinylene oligomers that act as conjugated wires of increasing length up to 53 Å. The unique finding here is that the net transport of the electron in the larger molecular wires is initiated by an electron-hole dissociation intermediated by hole delocalization (conformationally assisted and thermally dependent) forming transient mobile polaronic states in the bridge that terminate by an electron-hole recombination at the other wire extreme. On the contrary, for the shorter radical-anions our results suggest that a flickering resonance mechanism which is intermediate between hopping and superexchange is the operative one. We support these mechanistic interpretations by applying the pertinent biased kinetic models of the charge/spin exchange rates determined by electron paramagnetic resonance and by molecular structural level information obtained from UV-vis and Raman spectroscopies and by quantum chemical modeling.
authors.affiliation: Department of Molecular Nanoscience and Organic Materials, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN , Campus Universitari de Bellaterra, Cerdanyola, E-08193 Barcelona, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Franco
authors.affiliation: Department of Physical Chemistry, University of Malaga , Campus de Teatinos s/n, 29071 Malaga, Spain.
authors.forename: Paula Mayorga
authors.initials: PM
authors.lastname: Burrezo
authors.affiliation: Department of Molecular Nanoscience and Organic Materials, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN , Campus Universitari de Bellaterra, Cerdanyola, E-08193 Barcelona, Spain.
authors.forename: Vega
authors.initials: V
authors.lastname: Lloveras
authors.affiliation: Instituto de Nanociencia, Nanotecnología y Materiales Moleculares (INAMOL), University of Castilla-La Mancha , Campus de la Fábrica de Armas, 45071 Toledo, Spain.
authors.forename: Rubén
authors.initials: R
authors.lastname: Caballero
authors.affiliation: Department of Materials Science and Physical Chemistry, Faculty of Chemistry, University of Barcelona , Avenida Diagonal, 647, 08028 Barcelona, Spain.
authors.forename: Isaac
authors.initials: I
authors.lastname: Alcón
authors.affiliation: Department of Materials Science and Physical Chemistry, Faculty of Chemistry, University of Barcelona , Avenida Diagonal, 647, 08028 Barcelona, Spain.|Catalan Institution of Research and Advanced Studies (ICREA) , 08010 Barcelona, Spain.
authors.forename: Stefan T
authors.initials: ST
authors.lastname: Bromley
authors.affiliation: Department of Molecular Nanoscience and Organic Materials, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN , Campus Universitari de Bellaterra, Cerdanyola, E-08193 Barcelona, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Mas-Torrent
authors.affiliation: Instituto de Nanociencia, Nanotecnología y Materiales Moleculares (INAMOL), University of Castilla-La Mancha , Campus de la Fábrica de Armas, 45071 Toledo, Spain.
authors.forename: Fernando
authors.identifier: 0000-0002-7694-7722
authors.initials: F
authors.lastname: Langa
authors.affiliation: Department of Physical Chemistry, University of Malaga , Campus de Teatinos s/n, 29071 Malaga, Spain.
authors.forename: Juan T
authors.initials: JT
authors.lastname: López Navarrete
authors.affiliation: Department of Molecular Nanoscience and Organic Materials, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN , Campus Universitari de Bellaterra, Cerdanyola, E-08193 Barcelona, Spain.
authors.forename: Concepciò
authors.initials: C
authors.lastname: Rovira
authors.affiliation: Department of Physical Chemistry, University of Malaga , Campus de Teatinos s/n, 29071 Malaga, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Casado
authors.affiliation: Department of Molecular Nanoscience and Organic Materials, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN , Campus Universitari de Bellaterra, Cerdanyola, E-08193 Barcelona, Spain.
authors.forename: Jaume
authors.identifier: 0000-0003-1023-9923
authors.initials: J
authors.lastname: Veciana