Preparation of metallo porpyrins and photoinducued electron transfer from porphyrins to biointerface

光致电子转移系统将光能转化为高能电子，是自然光合作用获取太阳能的模型系统。电子受体连接光敏剂是一种利用光照产生长寿命电荷分离物质的良好体系。然而，电荷分离是在有机溶剂中而不是在水溶液中实现的。人们对如何在水溶液中实现电荷分离的实验有着浓厚的兴趣。我们报道了在水中产生长寿命的电荷分离物质，并有效地发生了光致析氢。疏水卟啉-丁基紫素-氨基丙基紫素三联体分子在水溶液中通过光诱导的两步电子转移反应生成了具有微秒时间尺度寿命的还原性紫素。紫连卟啉的结构如图1所示。紫紫素连接的卟啉具有从疏水性卟啉到氨基丙基紫紫素的逐渐亲水分子，并有利于电子在水中向氨基丙基紫紫素的定向转移，因为紫紫素与紫紫素之间以及卟啉环与紫紫素之间保持线性排列，没有分子内面对面的pi电子相互作用。逐渐亲水的形式也有利于溶剂笼，使电子从光激发卟啉转移到相邻的紫质，因此电子通过光激发单线态在水溶液中转移。并将卟啉应用于光致析氢体系中，观察到有效的析氢效果。

Photoinduced electron transfer systems, which changes light energy to high-energy electrons, are model systems of natural photosynthesis to harvest solar energy. Electron acceptor linked photosensitizers are one of good system to generate long lifetime charge separated species by light illumination. The charge separated species, however, are achieved in not water solution but organic solvent. There is intense interest in experiments which reveal how achieve charge separated species in aqueous solution. We report that long lifetime charge separated specie in water is generated and that photoinduced hydrogen evolution occurs effectively.Hydrophobic porphyrin-butylviologen-aminopropylviologen triad molecules undergo a photoinduced two-step electron transfer reaction which results in the generation of reduced viologen with a lifetime on the microsecond time scale in aqueous solution. Structure of the viologen linked porphyrin is shown in Fig. 1. The viologen linked porphyrin has a gradually hydrophilic molecule from hydrophobic porphyrin to aminopropylviologen, and facilitates a directional electron transfer to the aminopropylviologen in water, because the two viologen moieties stay under a linear arrangement which shows no intramolecular interaction with face to face of pi-electron between viologens and between the porphyrin ring and viologen. The gradually hydrophilic form also facilitates solvent cages for electron transfer from the phoexcited porphyrin to adjacent viologen, so that electron transfer via the photoexcited singlet state occurs in aqueous solution. The porphyrin was also applied for photoinduced hydrogen evolution system, and effective hydrogen evolution was observed.