Heinz Luisa G, Yushchenko Oleksandr, Neuburger Markus, Vauthey Eric, Wenger Oliver S
†Department of Chemistry, University of Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland.
‡Department of Physical Chemistry, University of Geneva, 30 quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland.
J Phys Chem A. 2015 Jun 4;119(22):5676-84. doi: 10.1021/acs.jpca.5b03649. Epub 2015 May 14.
Two donor bridge-acceptor molecules with terminal triarylamine and Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) redox partners were synthesized and investigated by cyclic voltammetry, optical absorption, luminescence, and transient absorption spectroscopy. The two dyads differ only by the central bridging unit, which was tetramethoxybenzene (tmb) in one case and unsubstituted phenylene (ph) in the other case. Photoirradiation of the Ru(bpy)3(2+) complex of the two dyads triggers intramolecular electron transfer from the triarylamine to the (3)MLCT-excited metal complex, and this process occurs with time constants of 1.5 and 6.8 ns for the tmb- and ph-bridged dyads, respectively. Thermal electron transfer in the reverse direction then leads to disappearance of the photoproduct with a time constant of 10 ns in both dyads. The faster rate of photoinduced charge transfer in the tmb-bridged dyad can be understood in the framework of a hole-tunneling model in which the electron-rich tmb bridge imposes a more shallow barrier than the less electron-rich ph spacer. Until now tmb-based molecular wires have received very little attention, and alkoxy substituents have been mostly used for improving the solubility of oligo-p-phenylene vinylene (OPV) and oligo-p-phenylene ethynylene (OPE) wires. Our study illustrates how four alkoxy-substituents on a phenylene backbone can have a significant influence on the charge-transfer properties of a molecular wire, and this is relevant in the greater context of a future molecular electronics technology.
合成了两种具有末端三芳基胺和Ru(bpy)3(2+)（bpy = 2,2'-联吡啶）氧化还原对的供体-桥-受体分子，并通过循环伏安法、光吸收、发光和瞬态吸收光谱对其进行了研究。这两种二元体系仅在中心桥连单元上有所不同，一种情况下是四甲氧基苯（tmb），另一种情况下是未取代的亚苯基（ph）。对这两种二元体系的Ru(bpy)3(2+)配合物进行光照射会引发分子内电子从三芳基胺转移到(3)MLCT激发态金属配合物，对于tmb桥连和ph桥连的二元体系，该过程的时间常数分别为1.5 ns和6.8 ns。然后，反向的热电子转移导致光产物消失，两种二元体系的时间常数均为10 ns。在空穴隧穿模型的框架内可以理解tmb桥连二元体系中光诱导电荷转移速率更快的现象，在该模型中，富电子的tmb桥比电子较少的ph间隔基团施加的势垒更浅。到目前为止，基于tmb的分子导线很少受到关注，烷氧基取代基主要用于提高聚对苯撑乙烯（OPV）和聚对苯撑乙炔（OPE）导线的溶解性。我们的研究表明，亚苯基主链上的四个烷氧基取代基如何对分子导线的电荷转移性质产生重大影响，这在未来分子电子技术的更大背景下具有重要意义。
