Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (USA), Fax: (+1) 847-491-1009; Present Address: Department of Chemistry Faculty of Science, Zagazig University, Zagazig (Egypt).
Chemistry. 2014 Nov 3;20(45):14690-7. doi: 10.1002/chem.201403744. Epub 2014 Sep 26.
Understanding the mechanism of efficient photoinduced electron-transfer processes is essential for developing molecular systems for artificial photosynthesis. Towards this goal, we describe the synthesis of a donor-acceptor dyad comprising a zinc porphyrin donor and a tetracationic cyclobis(paraquat-p-phenylene) (CBPQT(4+) ) acceptor. The X-ray crystal structure of the dyad reveals the formation of a dimeric motif through the intermolecular coordination between the triazole nitrogen and the central Zn metal of two adjacent units of the dyad. Photoinduced electron transfer within the dyad in MeCN was investigated by femtosecond and nanosecond transient absorption spectroscopy, as well as by transient EPR spectroscopy. Photoexcitation of the dyad produced a weakly coupled ZnP(+.) -CBPQT(3+.) spin-correlated radical-ion pair having a τ=146 ns lifetime and a spin-spin exchange interaction of only 0.23 mT. The long radical-ion-pair lifetime results from weak donor-acceptor electronic coupling as a consequence of having nine bonds between the donor and the acceptor, and the reduction in reorganization energy for electron transfer caused by charge dispersal over both paraquat units within CBPQT(3+.) .
理解高效光诱导电子转移过程的机制对于开发人工光合作用的分子系统至关重要。为此，我们描述了一种由锌卟啉给体和四阳离子环双（对亚甲基-paraquat-p-苯撑）（CBPQT(4+)）受体组成的给体-受体二聚体的合成。该二聚体的 X 射线晶体结构显示通过二聚体中两个相邻单元的三唑氮和中心 Zn 金属之间的分子间配位形成二聚体基序。通过飞秒和纳秒瞬态吸收光谱以及瞬态 EPR 光谱研究了二聚体在 MeCN 中的光诱导电子转移。二聚体的光激发产生了一个弱耦合的 ZnP(+.) -CBPQT(3+.) 自旋相关自由基离子对，其 τ=146 ns 寿命和自旋-自旋交换相互作用仅为 0.23 mT。自由基离子对的长寿命是由于供体和受体之间有九个键，导致供体和受体之间的电子耦合较弱，并且 CBPQT(3+.) 中的两个对亚甲基-paraquat 单元内的电荷分散导致电子转移的重组能降低。
