Rigidified tetrathiafulvalene–[60]fullerene assemblies: towards the control of through-space orientation between both electroactive units
作者:David Kreher、Michel Cariou、Sheng-Gao Liu、Eric Levillain、Jaume Veciana、Concepció Rovira、Alain Gorgues、Piétrick Hudhomme
DOI:10.1039/b201695h
日期:2002.6.21
Our recent works on fused TTFâC60 dyads, (TTF)nâC60 polyads and C60âTTFâC60 dumbbell triads in which the acceptor C60 is doubly tethered to the donor tetrathiafulvalene through a rigidified cyclohexene ring are presented. This approach was developed in order to control the relative orientation as well as the distance between both donor and acceptor entities. Thereby, through-space interactions which are of great importance for photoinduced electron- and/or energy-transfer processes are expected to dominate because of the special topology of the molecules. The two linked C60 and TTF chromophores in such adducts are not only in close proximity but also have optimal orbital orientations, thus facilitating these through-space electronic interactions. These new C60-based assemblies were synthesized by [4 + 2] DielsâAlder cycloaddition
reactions. The different methodologies considered for their synthesis are discussed, their analytical, spectroscopic characterizations and electrochemical properties are also described. The selective electro-oxidation or reduction afforded the corresponding radical cation and radical anion which were characterized by EPR. These C60-based assemblies were studied for their nonlinear optical and optical limiting applications. Moreover, intramolecular photoinduced charge-separation and charge-recombination processes in a fused C60âTTFâC60 dumbbell triad which was designed to be soluble in organic solvents were investigated by time-resolved absorption and fluorescence techniques. Appreciable interaction between the C60 moiety and TTF moiety in the ground state was suggested by steady-state absorption spectra and the fluorescence spectra showed considerable interaction in the singlet excited state. The nanosecond transient absorption spectra
displayed the formation of the charge-separated radical pair C60âTTFË+âC60Ëâ, characterized by a lifetime of ca. 20 ns in benzonitrile.
我们最近的研究工作集中在融合的TTF–C60二聚体、(TTF)n–C60多聚体和C60–TTF–C60哑铃三聚体,这些体系中受体C60通过刚性的环己烯环与供体四硫富瓦烯双重连接。此方法的开发旨在控制供体和受体之间的相对方向和距离。因此,由于分子的特殊拓扑结构,空间内的相互作用在光诱导电子及/或能量转移过程中预计将占主导地位。这种加合物中连接的C60和TTF色团不仅相互接近,而且具有最佳的轨道取向,从而促进这些跨空间的电子相互作用。这些新的基于C60的组装体是通过[4 + 2]迪尔斯-阿尔德环加成反应合成的。文中讨论了其合成过程中考虑的不同方法,并描述了它们的分析、光谱特性及电化学性质。选择性电氧化或还原生成了相应的自由基阳离子和自由基阴离子,这些都通过电子顺磁共振(EPR)进行了表征。这些基于C60的组装体也被研究用于其非线性光学和光限制应用。此外,设计为可溶于有机溶剂的融合C60–TTF–C60哑铃三聚体中的分子内光诱导电荷分离和电荷重组过程通过时间分辨吸收和荧光技术进行了研究。在基态中,稳态吸收光谱表明C60基团与TTF基团之间存在显著的相互作用,而荧光光谱则显示在单重激发态中也存在较强的相互作用。纳秒瞬态吸收光谱显示了电荷分离的自由基对C60–TTFË+–C60Ë–,其在苯腈中表征的寿命约为20纳秒。