Using Meta Conjugation To Enhance Charge Separation versus Charge Recombination in Phenylacetylene Donor−Bridge−Acceptor Complexes

A pair of donor−bridge−acceptor electron-transfer complexes, with a carbazole donor and a naphthalimide acceptor connected by either a para- or meta-conjugated phenylacetylene bridge, are synthesized and studied using time-resolved and steady-state spectroscopy. These experiments show that the charge separation times, which depend on the coupling of the donor and acceptor through the excited bridge moiety, are similar for the two molecules (Meta and Para). The charge recombination time, however, is a factor of 10 slower for Meta than for Para. These results are related to changes in the electronic coupling of the bridge depending on its electronic state, and show that meta-conjugated bridges provide a possible motif for the design of asymmetric molecular wires.研究团队合成了一对给体-桥-受体型电子转移配合物：其给体为咔唑 (carbazole)、受体为萘酰亚胺 (naphthalimide)，并分别通过对位共轭或间位共轭的苯乙炔 (phenylacetylene) 桥连接，随后采用时间分辨光谱与稳态光谱技术对其展开研究。实验结果表明，电荷分离时间取决于给体与受体通过激发态桥单元的电子耦合作用，两种分子 (Meta与Para) 的电荷分离时间相近。然而，间位型分子的电荷复合时间相较对位型分子慢一个数量级。上述结果与桥单元的电子耦合作用随其电子态变化的规律密切相关，同时证明间位共轭桥可为不对称分子导线的设计提供可行的结构基元。