Beckers Edwin H A, Meskers Stefan C J, Schenning Albertus P H J, Chen Zhijian, Würthner Frank, Marsal Philippe, Beljonne David, Cornil Jérôme, Janssen René A J
Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, The Netherlands.
J Am Chem Soc. 2006 Jan 18;128(2):649-57. doi: 10.1021/ja0568042.
The kinetics of photoinduced charge transfer reactions in covalently linked donor-acceptor molecules often undergoes dramatic changes when these molecules self-assemble from a molecular dissolved state into a nanoaggregate. Frequently, the origin of these changes is only partially understood. In this paper, we describe the intermolecular spatial organization of three homologous arrays, consisting of a central perylene bisimide (PERY) acceptor moiety and two oligo(p-phenylene vinylene) (OPV) donor units, in nanoaggregates and identify both face-to-face (H-type) and slipped (J-type) stacking of the OPV and PERY chromophores. For the J-type aggregates, short intermolecular OPV-PERY distances are created that give rise to a charge-transfer absorption band. The proximity of the donor and acceptor groups in the J-type aggregates enables a highly efficient photoinduced charge separation with a rate (k(cs) > 10(12) s(-1)) that significantly exceeds the rate of the intramolecular charge transfer of the same compounds when molecularly dissolved, even in the most polar media. In the H-type aggregates, on the other hand, the intermolecular OPV-PERY distance is not reduced compared to the intramolecular separation, and hence, the rates of the electron transfer reactions are not significantly affected compared to the molecular dissolved state. Similar to the forward electron transfer, the kinetics of the charge recombination in the aggregated state can be understood by considering the different interchromophoric distances that occur in the H- and J-type aggregates. These results provide the first consistent rationalization of the remarkable differences that are observed for photoinduced charge-transfer reactions of donor-acceptor compounds in molecularly dissolved versus aggregated states.
当共价连接的供体 - 受体分子从分子溶解状态自组装成纳米聚集体时，光诱导电荷转移反应的动力学通常会发生显著变化。这些变化的起源往往仅得到部分理解。在本文中，我们描述了由一个中心苝二酰亚胺（PERY）受体部分和两个对苯撑乙烯撑（OPV）供体单元组成的三个同源阵列在纳米聚集体中的分子间空间组织，并确定了OPV和PERY发色团的面对面（H型）和错位（J型）堆积。对于J型聚集体，形成了短的分子间OPV - PERY距离，从而产生电荷转移吸收带。J型聚集体中供体和受体基团的接近使得光诱导电荷分离效率极高，其速率（k(cs) > 10(12) s(-1)）显著超过相同化合物在分子溶解状态下（即使在极性最强的介质中）的分子内电荷转移速率。另一方面，在H型聚集体中，分子间OPV - PERY距离与分子内距离相比并未减小，因此，与分子溶解状态相比，电子转移反应速率没有受到显著影响。与正向电子转移类似，通过考虑H型和J型聚集体中不同的发色团间距离，可以理解聚集态下电荷复合的动力学。这些结果首次对供体 - 受体化合物在分子溶解态与聚集态下光诱导电荷转移反应所观察到的显著差异给出了一致的合理解释。
