Narra Sudhakar, Nishimura Yoshifumi, Witek Henryk A, Shigeto Shinsuke
Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu 30010 (Taiwan).
Chemphyschem. 2014 Oct 6;15(14):2945-50. doi: 10.1002/cphc.201402411. Epub 2014 Jul 17.
Back electron transfer (BET) is one of the important processes that govern the decay of generated ion pairs in intermolecular photoinduced electron transfer reactions. Unfortunately, a detailed mechanism of BET reactions remains largely unknown in spite of their importance for the development of molecular photovoltaic structures. Here, we examine the BET reaction of pyrene (Py) and 1,4-dicyanobenzene (DCB) in acetonitrile (ACN) by using time-resolved near- and mid-IR spectroscopy. The Py dimer radical cation (Py2(·+)) and DCB radical anion (DCB(·-)) generated after photoexcitation of Py show asynchronous decay kinetics. To account for this observation, we propose a reaction mechanism that involves electron transfer from DCB(·-) to the solvent and charge recombination between the resulting ACN dimer anion and Py2(·+). The unique role of ACN as a charge mediator revealed herein could have implications for strategies that retard charge recombination in dye-sensitized solar cells.
反向电子转移（BET）是分子间光致电子转移反应中控制所产生离子对衰变的重要过程之一。遗憾的是，尽管BET反应对分子光伏结构的发展至关重要，但其详细机制在很大程度上仍不为人知。在此，我们通过使用时间分辨近红外和中红外光谱研究了芘（Py）与1,4-二氰基苯（DCB）在乙腈（ACN）中的BET反应。Py光激发后产生的Py二聚体自由基阳离子（Py2(·+)）和DCB自由基阴离子（DCB(·-)）表现出异步衰变动力学。为了解释这一观察结果，我们提出了一种反应机制，该机制涉及电子从DCB(·-)转移到溶剂以及所得ACN二聚体阴离子与Py2(·+)之间的电荷复合。本文揭示的ACN作为电荷介质的独特作用可能对染料敏化太阳能电池中延缓电荷复合的策略具有启示意义。
