phenyl-phenyl coupling is found to be roughly 7 times stronger than xylyl-xylyl coupling. This difference in electronic coupling strengths can be explained satisfactorily on the sole basis of conformational effects. It is consistent with equilibrium torsion angles of 35–40° between two phenyls and 65–70° between two xylyls.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
在七个分子中研究了跨可变长度低聚对亚
苯基和低聚
对二甲苯桥的光触发分子内电子转移。对于这两种类型的桥,电荷转移率随着间隔单元数量的增加呈指数下降。亚
苯基的距离衰减参数为 0.21 A–1,二
甲苯的距离衰减参数为 0.77 A–1。基于超交换理论的简单分析表明,这种差异是由于相邻桥接单元之间的电子耦合不均造成的。根据实验数据,发现
苯基-
苯基偶联比二
甲苯基-二
甲苯基偶联强大约 7 倍。仅基于构象效应就可以令人满意地解释电子耦合强度的这种差异。