Center for Chemical Dynamics and Nanomaterials Research, Department of Chemistry, Case Western Reserve University , 10900 Euclid Avenue, Cleveland, Ohio 44106, United States.
Department of Chemistry, University of Miami , Coral Gables, Florida 33124, United States.
J Phys Chem B. 2018 Jan 11;122(1):328-337. doi: 10.1021/acs.jpcb.7b11306. Epub 2017 Dec 22.
Results of our study on ultrafast electron transfer (eT) dynamics from coumarins (coumarin-1, coumarin-480, and coumarin-153) incarcerated within octa acid (OA) capsules as electron donors to methyl viologen dissolved in water as acceptor are presented. Upon photoexcitation, coumarin inside the OA capsule transfers an electron to the acceptor electrostatically attached to the capsule leading to a long-lived radical-ion pair separated by the OA capsular wall. This charge-separated state returns to the neutral ground state via back electron transfer on the nanosecond time scale. This system allows for ultrafast electron transfer processes through a molecular wall from the apolar capsular interior to the highly polar (aqueous) environment on the femtosecond time scale. Employing femtosecond transient absorption spectroscopy, distinct rates of both forward (1-25 ps) and backward eT (700-1200 ps) processes were measured. Further understanding of the energetics is provided using Rehm-Weller analysis for the investigated photoinduced eT reactions. The results provide the rates of the eT across a molecular wall, akin to an isotropic solution, depending on the standard free energy of the reaction. The insights from this work could be utilized in the future design of efficient electron transfer processes across interfaces separating apolar and polar environments.
我们的研究结果表明，香豆素（香豆素 1、香豆素 480 和香豆素 153）在作为电子供体的辛酸（OA）胶囊内超快电子转移（eT）动力学，以及溶解在水中的作为受体的甲紫精之间存在关系。光激发后，OA 胶囊内的香豆素通过静电作用将电子转移到与胶囊相连的受体上，导致自由基离子对被 OA 胶囊壁隔开。这个荷电分离态通过纳秒时间尺度上的反向电子转移回到中性基态。这个系统允许超快的电子转移过程通过分子壁从非极性的胶囊内部到极性（水）环境中，时间尺度在飞秒范围内。采用飞秒瞬态吸收光谱法，测量了正向（1-25 ps）和反向 eT（700-1200 ps）过程的明显速率。使用 Rehm-Weller 分析对所研究的光诱导 eT 反应进行了进一步的能量理解。结果提供了跨分子壁的 eT 速率，类似于各向同性溶液，取决于反应的标准自由能。这项工作的见解可以在未来设计分离非极性和极性环境的界面处的有效电子转移过程中得到利用。
