Wolffs Martin, Delsuc Nicolas, Veldman Dirk, Nguyên Vân Anh, Williams René M, Meskers Stefan C J, Janssen René A J, Huc Ivan, Schenning Albertus P H J
Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
J Am Chem Soc. 2009 Apr 8;131(13):4819-29. doi: 10.1021/ja809367u.
Here we report the synthesis and characterization of four quinoline-derived foldamers with increasing oligomeric length; dimer O2P, tetramer O4P, pentamer O5P, and nonamer O9P functionalized with on one end an oligo(p-phenylene vinylene) (OPV) and on the other end a perylene bisimide (PB) chromophore. (1)H NMR confirms the formation of the expected folded structures in both toluene and chloroform solution. The structural predictability and rigidity of the oligomeric series enabled us to investigate the effect of a helical bridge and chromophore position on the photoinduced processes in the electron OPV-PB donor-acceptor pair in chloroform and toluene. The helical properties of the bridge ensured that the chromophore separation distance through space is different from the separation distance through the bridge. For all foldamer-solvent combinations studied, excitation of either OPV or PB results in nearly quantitative quenching of the fluorescence indicating a fast charge separation reaction between the OPV and PB. Femtosecond photoinduced absorption measurements confirmed the fast formation of a charge-separated state. The recombination reaction involves a combination of direct decay to the ground state and the formation of an intermediate triplet state, with their balance depending on the foldamer-solvent combination. Molecular orbital calculations rationalize the fast photoinduced charge separation, by revealing that the bridging foldamer mediates the charge transfer from donor to acceptor via the superexchange mechanism. Remarkably low attenuation factors (beta(CS) approximately 10(-2) A(-1)) were obtained using either through space or through bridge separation distance. However, in these calculations only three of the four foldamers show the expected linear behavior between the logarithm of the charge separation rate constant and the distance between the chromophores. The combined results show when a helical bridge is separating the charge transfer couple, hampering the usefulness of a uniform description of the charge-separation phenomena.
在此，我们报道了四种喹啉衍生的折叠体的合成与表征，这些折叠体的寡聚长度不断增加；二聚体O2P、四聚体O4P、五聚体O5P和九聚体O9P，一端用聚对苯撑乙烯（OPV）功能化，另一端用苝二酰亚胺（PB）发色团功能化。核磁共振氢谱（¹H NMR）证实了在甲苯和氯仿溶液中均形成了预期的折叠结构。该寡聚体系列的结构可预测性和刚性使我们能够研究螺旋桥和发色团位置对氯仿和甲苯中电子OPV - PB供体 - 受体对光诱导过程的影响。桥的螺旋性质确保了发色团通过空间的分离距离与通过桥的分离距离不同。对于所研究的所有折叠体 - 溶剂组合，激发OPV或PB都会导致荧光几乎完全猝灭，这表明OPV和PB之间发生了快速的电荷分离反应。飞秒光诱导吸收测量证实了电荷分离态的快速形成。复合反应涉及直接衰减到基态和形成中间三重态的组合，它们之间的平衡取决于折叠体 - 溶剂组合。分子轨道计算通过揭示桥连折叠体通过超交换机制介导从供体到受体的电荷转移，从而解释了快速的光诱导电荷分离。无论是通过空间还是通过桥的分离距离，都获得了极低的衰减因子（β(CS)约为10⁻² Å⁻¹）。然而，在这些计算中，四种折叠体中只有三种在电荷分离速率常数的对数与发色团之间的距离之间呈现出预期的线性行为。综合结果表明，当螺旋桥分隔电荷转移对时，妨碍了对电荷分离现象进行统一描述的有效性。
