New Strategy for Control of Electron Transfer in Photosynthetic Models -Local Electric Field and Hydrogen Bond

1)合成了含季铵中心的卟啉（H）-均苯四甲酸酰亚胺（I）二元配合物，并通过测定它们在各种溶剂中的荧光光谱，研究了它们的分子内电子转移反应。电荷位点增强了电子转移，但其影响在极性溶剂如DMF和THF中相对较小，但在低极性介质如苯和己烷中非常大。皮秒时间分辨的瞬态吸收光谱表明形成了电荷分离态，H+-I-，给出了荧光猝灭的电子转移的有力证据。通过多步合成，将电荷位点引入到更精细的光合作用模型中，如二聚体-单体-均苯四酰亚胺三元组。这些模型的电子转移动力学目前正在研究中。2）制备了一种带有2，6-二酰氨基吡啶结合位点的卟啉主体，并发现其在非极性溶剂中与萘二酰亚胺客体络合。在苯中，缔合常数约为10^3M。用皮秒时间分辨荧光寿命和瞬态吸收光谱研究了络合物内的电子转移。氢键上的电子转移被认为是相当有效的，可比的共价连接的模型具有相同的能隙，但离子对状态被发现是相当短的寿命相比，在共价连接的对应物。

1) Porphyrin (H) -pyromellitimide (I) dyads bearing a quaternary ammonium site have been prepared and their intramolecular electron transfer reaction has been studied by measuring their fluorescence spectra in a wide range of solvents. The charges site enhances the electron transfer, but its effects are relatively small in polar solvents such as DMF and THF but are very large in low polarity media such as benzene and hexane. Pico-second time resolved transient absorption spectra revealed the formation of a charge separated state, H+-I-, giving firm evidence of the electron transfer for the fluorescence quenching. Introduction of a charges site into a more elaborated photosynthetic models such as dimer-monomer-pyromellitimide triad has been achieved through multi-step synthesis. The electron transfer dynamics of these models are now in being pursued.2) A porphyrin host bearing 2,6-diacylaminopyridine binding site was prepared and was found to be complexed with naphthalene-diimide guest in nonpolar solvents. In benzene, the association constant is ca.10^3M.Intracomplex electron transfer has been studied by the picosecond time-resolved fluorescence lifetime and the transient absorption spectra. Electron transfer over hydrogen-bond is found to be quite effective, comparable to that of covalently-linked models having the same energy gap, but the ion-pair state was found to be rather short-lived in comparison to that in the covalently linked counterpart.