Imahori Hiroshi, Sekiguchi Yuji, Kashiwagi Yukiyasu, Sato Tohru, Araki Yasuyuki, Ito Osamu, Yamada Hiroko, Fukuzumi Shunichi
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, PRESTO, Japan Science and Technology Corporation, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
Chemistry. 2004 Jul 5;10(13):3184-96. doi: 10.1002/chem.200305308.
A meso,meso-linked porphyrin trimer, (ZnP)3, as a light-harvesting chromophore, has been incorporated for the first time into a photosynthetic multistep electron-transfer model including ferrocene (Fc) as an electron donor and fullerene (C60) as an electron acceptor, to construct the ferrocene-meso,meso-linked porphyrin trimer-fullerene system Fc-(ZnP)3-C60. Photoirradiation of Fc-(ZnP)3-C60 results in photoinduced electron transfer from both the singlet and triplet excited states of the porphyrin trimer, 1(ZnP)3* and 3(ZnP)3*, to the C60 moiety to produce the porphyrin trimer radical cation-C60 radical anion pair, Fc-(ZnP)3*+-C60*-. Subsequent formation of the final charge-separated state Fc+-(ZnP)3-C60*- was confirmed by the transient absorption spectra observed by pico- and nanosecond time-resolved laser flash photolysis. The final charge-separated state decays, obeying first-order kinetics, with a long lifetime (0.53 s in DMF at 163 K) that is comparable with that of the natural bacterial photosynthetic reaction center. More importantly, the quantum yield of formation of the final charge-separated state (0.83 in benzonitrile) remains high, despite the large separation distance between the Fc+ and C60*- moieties. Such a high quantum yield results from efficient charge separation through the porphyrin trimer, whereas a slow charge recombination is associated with the localized porphyrin radical cation in the porphyrin trimer. The light-harvesting efficiency in the visible region has also been much improved in Fc-(ZnP)3-C60 because of exciton coupling in the porphyrin trimer as well as an increase in the number of porphyrins.
一种中位-中位连接的卟啉三聚体(ZnP)3作为光捕获发色团，首次被引入到一个光合多步电子转移模型中，该模型以二茂铁(Fc)作为电子供体，富勒烯(C60)作为电子受体，构建了二茂铁-中位-中位连接的卟啉三聚体-富勒烯体系Fc-(ZnP)3-C60。对Fc-(ZnP)3-C60进行光照射会导致卟啉三聚体的单重态和三重态激发态1(ZnP)3和三重态激发态3(ZnP)3向C60部分发生光诱导电子转移，生成卟啉三聚体自由基阳离子-C60自由基阴离子对Fc-(ZnP)3*+-C60*-。通过皮秒和纳秒时间分辨激光闪光光解观察到的瞬态吸收光谱证实了最终电荷分离态Fc+-(ZnP)3-C60*-的形成。最终电荷分离态按一级动力学衰减，具有较长的寿命(在163K的N,N-二甲基甲酰胺中为0.53s)，这与天然细菌光合反应中心的寿命相当。更重要的是，尽管Fc+和C60*-部分之间的分离距离很大，但最终电荷分离态的形成量子产率(在苯甲腈中为0.83)仍然很高。如此高的量子产率源于通过卟啉三聚体的有效电荷分离，而缓慢的电荷复合与卟啉三聚体中局域化的卟啉自由基阳离子有关。由于卟啉三聚体中的激子耦合以及卟啉数量的增加，Fc-(ZnP)3-C60在可见光区域的光捕获效率也有了很大提高。
