Department of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, TX 76203-5017, USA.
Chemistry. 2013 May 27;19(22):7221-30. doi: 10.1002/chem.201204317. Epub 2013 Mar 28.
Donor-acceptor distance, orientation, and photoexcitation wavelength are key factors in governing the efficiency and mechanism of electron-transfer reactions both in natural and synthetic systems. Although distance and orientation effects have been successfully demonstrated in simple donor-acceptor dyads, revealing excitation-wavelength-dependent photochemical properties demands multimodular, photosynthetic-reaction-center model compounds. Here, we successfully demonstrate donor- acceptor excitation-wavelength-dependent, ultrafast charge separation and charge recombination in newly synthesized, novel tetrads featuring bisferrocene, BF2 -chelated azadipyrromethene, and fullerene entities. The tetrads synthesized using multistep synthetic procedure revealed characteristic optical, redox, and photo reactivities of the individual components and featured "closely" and "distantly" positioned donor-acceptor systems. The near-IR-emitting BF2-chelated azadipyrromethene acted as a photosensitizing electron acceptor along with fullerene, while the ferrocene entities acted as electron donors. Both tetrads revealed excitation-wavelength-dependent, photoinduced, electron-transfer events as probed by femtosecond transient absorption spectroscopy. That is, formation of the Fc(+)-ADP-C60(.-) charge-separated state upon C60 excitation, and Fc(+)-ADP(.-)-C60 formation upon ADP excitation is demonstrated.
供体-受体距离、取向和光激发波长是控制自然和合成体系中电子转移反应效率和机制的关键因素。虽然在简单的供体-受体偶联物中已经成功地证明了距离和取向效应，但揭示光激发波长依赖性光化学性质需要多模块、光合作用反应中心模型化合物。在这里，我们成功地证明了新合成的具有双二茂铁、BF2-螯合偶氮二吡咯甲川和富勒烯实体的新型四联体中供体-受体激发波长依赖性超快电荷分离和电荷复合。通过多步合成程序合成的四联体显示出各个组件的特征光学、氧化还原和光反应性，并具有“紧密”和“远离”定位的供体-受体系统。近红外发射的 BF2-螯合偶氮二吡咯甲川与富勒烯一起作为光敏电子受体，而二茂铁实体作为电子供体。两个四联体都通过飞秒瞬态吸收光谱研究揭示了激发波长依赖性的光诱导电子转移事件。也就是说，在 C60 激发时形成 Fc(+)-ADP-C60(.-)电荷分离态，在 ADP 激发时形成 Fc(+)-ADP(.-)-C60。
