Tunneling versus Hopping in Mixed-Valence Oligo-p-phenylenevinylene Polychlorinated Bis(triphenylmethyl) Radical Anions
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- 作者：Vega Lloveras ; Jos茅 Vidal-Gancedo ; Teresa M. Figueira-Duarte ; Jean-Fran莽ois Nierengarten ; Juan J. Novoa ; Fernando Mota ; Nora Ventosa ; Concepci贸 Rovira ; Jaume Veciana
- 刊名：Journal of the American Chemical Society
- 出版年：2011
- 出版时间：April 20, 2011
- 年：2011
- 卷：133
- 期：15
- 页码：5818-5833
- 全文大小：1340K
- 年卷期：v.133,no.15(April 20, 2011)
- ISSN：1520-5126
文摘
Radical anions <b>1b>p>鈭掆€?/sup>鈭?b>5b>p>鈭掆€?/sup>, showing different lengths and incorporating up to five p-phenylenevinylene (PPV) bridges between two polychlorinated triphenylmethyl units, have been prepared by chemical or electrochemical reductions from the corresponding diradicals <b>1b>鈭?b>5b> which were prepared using Wittig鈭扝orner-type chemistry. Such radical anions enabled us to study, by means of UV鈭抳is鈭扤IR and variable-temperature electron spin resonance spectroscopies, the long-range intramolecular electron transfer (IET) phenomena in their ground states, probing the influence of increasing the lengths of the bridges without the need of using an external bias to promote IET. The temperature dependence of the IET rate constants of mixed-valence species <b>1b>p>鈭掆€?/sup>鈭?b>5b>p>鈭掆€?/sup> revealed the presence of two different regimes at low and high temperatures in which the mechanisms of electron tunneling via superexchange and thermally activated hopping are competing. Both mechanisms occur to different extents, depending on the sizes of the radical anions, since the lengths of the oligo-PPV bridges notably influence the tunneling efficiency and the activation energy barriers of the hopping processes, the barriers diminishing when the lengths are increased. The nature of solvents also modifies the IET rates by means of the interactions between the oligo-PPV bridges and the solvents. Finally, in the shortest compounds <b>1b>p>鈭掆€?/sup> and <b>2b>p>鈭掆€?/sup>, the IET induced optically through the superexchange mechanism can also be observed by the exhibited intervalence bands, whose intensities decrease with the length of the PPV bridge.