Synthesis of oligothiophene-bridged bisporphyrins and study of the linkage dependence of the electronic coupling.
Synthesis of oligothiophene-bridged bisporphyrins and study of the linkage dependence of the electronic coupling.
复制标题
低聚噻吩桥联双卟啉的合成及电子耦合的键依赖性研究。
作者：
F. Odobel;S. Suresh;E. Blart;Y. Nicolas;J. Quintard;P. Janvier;J. Le Questel;B. Illien;D. Rondeau;P. Richomme;T. Häupl;S. Wallin;L. Hammarström
已经制备了一组12个卟啉二聚体，以提供关于卟啉核心和桥之间的连接类型如何影响卟啉间电子相互作用的信息。新的卟啉体系直接在介孔位置上被低聚硫吩链取代，该链由单一的C-C sigma键、反式乙烯基或乙炔基团连接。这些化合物很容易通过钯催化的交叉偶联反应(Stille、Heck和Sonogashira)在5-iodo-10，15，20-(3，5-ditert-butylphenyl)porphyrin和适当的低聚硫吩衍生物之间得到。这种合成方法对于制备低聚硫吩基的卟啉体系是一种简单而有效的方法。二聚体的吸收光谱和荧光性质证明了用于连接桥连到卟啉单元的化学键的特性的关键重要性。因此，通过改变用于连接发色团和桥的键连接性的类型，可以显著地调制电子通信的大小。目前的工作表明，低聚硫吩间隔体是连接卟啉的一类可行的连接物，而带有乙炔基键的季噻吩基在长达28A的距离上提供了高的电子相互作用。对这些二聚体的详细计算研究阐明了共轭体系作为分子导线所需的条件。这些条件是分子的完全平面性，以及桥和卟啉的前线轨道之间适当的能量匹配。用荧光光谱法研究了锌卟啉和游离碱卟啉组成的不对称二元体的分子间能量传递。在所有体系中，该过程的效率超过98%，其速率常数以4ZH>；1ZH>；3ZH约2ZH的数量级稳定下降。因此，最大的反应速率(kent=1.2x10(11)S-1)出现在与二乙炔基季噻吩键相连的二联体上，这是该系列中最长的桥。这些结果清楚地表明，如果选择适当的分子连接器的电子结构，可以在很长的距离内促进强通信和高效的光诱导过程。
A set of twelve porphyrin dimers has been prepared to give information on how the type of connectivity between a porphyrin core and a bridge can influence the interporphyrin electronic interaction. The new porphyrin systems are substituted directly at the meso position with an oligothiophene chain tethered either with a single C-C sigma bond, a trans ethylenyl group, or a acetylenyl group. The compounds are easily obtained by palladium-catalyzed cross-coupling reactions (Stille, Heck, and Sonogashira) between 5-iodo-10,15,20-(3,5-ditert-butylphenyl)porphyrin and the appropriate oligothiophene derivative. This synthetic approach is straightforward and very effective for preparing oligothiophene-based prophyrin systems. The absorption spectra and the fluorescence properties of the dimers demonstrated the crucial importance of the characteristics of the chemical bond used to connect the bridge to the porphyrin unit. The magnitude of the electronic communication can thus be significantly modulated by altering the type of bond connectivity used to link the chromophore to the bridge. The present work shows that an oligothiophene spacer is a viable class of linker for connecting porphyrins, and that a quaterthiophene appended with ethynyl linkages affords a high electronic interaction over a distance as large as 28 A. A detailed computational study of these dimers has clarified the conditions needed for a conjugated system to behave as a molecular wire. These conditions are full planarity of the molecule and proper energy matching between the frontier orbitals of the bridge and the porphyrin. Intermolecular energy transfer in asymmetrical dyads composed of a zinc porphyrin and a freebase porphyrin has been studied by fluorescence spectroscopy. In all systems, this process is more than 98% efficient, and its rate constant decreases steadily in the order 4ZH > 1ZH > 3ZH approximately 2ZH. Thus, the largest rate (kEnT = 1.2 x 10(11) s-1) was found in the dyad linked with bisethynyl quaterthiophene, which represents the longest bridge within the series. These results clearly demonstrate that strong communication and also efficient photoinduced processes can be promoted over a large distance if the electronic structure of the molecular connector is appropriately chosen.