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Operative Mechanism of Hole-Assisted Negative Charge Motion in Ground States of Radical-Anion Molecular Wires

AuthorsFranco, Carlos ; Lloveras, Vega ; Mas Torrent, Marta ; Rovira, Concepció ; Veciana, Jaume
KeywordsIntramolecular electron-transfer
Thienylenevinylene oligomers
Length dependence
Issue Date18-Jan-2017
PublisherAmerican Chemical Society
CitationJournal of the American Chemical Society 139(2): 686-692 (2017)
AbstractCharge 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 tran-sient mobile polaronic states in the bridge that terminate by an electron-hole recombination at the other wire extreme. On the con-trary for the shorter radical-anions our results suggest that a flickering resonance mechanism which is intermediate between hop-ping 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 infor-mation obtained from UV-Vis and Raman spectroscopies and by quantum chemical modelling.
DescriptionFranco, Carlos et al.
Publisher version (URL)http://dx.doi.org/10.1021/jacs.6b08649
Appears in Collections:(ICMAB) Artículos
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