Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram 695 019, India.
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 200 002, India.
J Phys Chem B. 2021 May 6;125(17):4428-4437. doi: 10.1021/acs.jpcb.1c00581. Epub 2021 Apr 22.
Pyrene linked to two β-CD (CD = cyclodextrin; PY = pyrene) molecules (CD-PY-CD) and methylviologen (MV) linked to two adamantane (AD) groups (AD-MV-AD) self-assembled in water to give toroidal nanostructures. Photoprocesses taking place in the femtosecond and nanosecond time ranges within the assembly are reported. Fluorescence of the pyrene chromophore was quenched in the toroid, suggesting very efficient electron transfer. Fast quenching of the pyrene fluorescence with a time constant of 6.85 ns was attributed to photoinduced electron transfer from pyrene to methyl viologen within the toroid assembly. Electron transfer leads to the formation of radical ion products, PY and MV, which were identified in the nanosecond transient absorption spectra. Because of the close packing of chromophores, the radical ions undergo fast reactions with chromophores or similar ions in adjacent stacks to give dimeric products. Since the dimeric species are not very stable, the reactions are reversed at longer time scales to generate the radical ions, which then undergo back electron transfer and regenerate the starting materials.
芘与两个 β-环糊精（CD=环糊精；PY=芘）分子（CD-PY-CD）和两个金刚烷（AD）基团连接的甲紫精（MV）（AD-MV-AD）在水中自组装形成环形纳米结构。报告了在组装体中纳秒和飞秒时间范围内发生的光过程。在环形纳米结构中，芘发色团的荧光被猝灭，表明存在非常有效的电子转移。芘荧光的快速猝灭，时间常数为 6.85 ns，归因于在环形组装体中从芘到甲紫精的光致电子转移。电子转移导致自由基离子产物 PY 和 MV 的形成，它们在纳秒瞬态吸收光谱中被识别。由于发色团的紧密堆积，自由基离子与相邻堆叠中的发色团或类似离子快速反应生成二聚体产物。由于二聚体物种不太稳定，反应在较长时间尺度上逆转，生成自由基离子，然后经历反向电子转移并再生起始材料。
