Synthesis and intramolecular charge-transfer properties of new tetrathiafulvalene–σ-tetracyanoanthraquinodimethane diad (TTF–σ-TCNAQ) and triad (TTF–σ-TCNAQ–σ-TTF) molecules
作者:Pilar de Miguel、Martin R. Bryce、Leonid M. Goldenberg、Andrew Beeby、Vladimir Khodorkovsky、Lev Shapiro、Angelika Niemz、Alej,ro O. Cuello、Vincent Rotello
DOI:10.1039/a704013j
日期:——
We report the use of functionalised electron acceptor tetracyanoanthraquinodimethane (TCNAQ) units in the synthesis of novel diad DâÏ-A compounds 6 and 7 [D=tetrathiafulvalenyl (TTF) and ferrocenyl] and the triad TTFâÏ-TCNAQâÏ-TTF assembly 8. Compounds 6â8 display a very weak, broad, low-energy intramolecular charge-transfer band in the UVâVIS spectra. Nanosecond laser flash photolysis of compound 6 did not lead to any new transient absorptions in the 300â800 nm region, suggesting that if a charge-separated species is formed upon excitation, then back electron transfer occurs very rapidly to regenerate the ground state. Cyclic voltammetry of compounds 6â8 shows that reversible oxidation processes occur for the TTF and ferrocene moieties, and a reversible two-electron reduction occurs for the TCNAQ moiety. Spectroelectrochemical studies on compound 6 have enabled the redox processes to be assigned to the sequential formation of the TTF radical cation and dication upon oxidation, and the TCNAQ dianion upon reduction. Simultaneous electrochemistry and EPR (SEEPR) experiments provide further evidence for intramolecular interaction between the TTF and TCNAQ moieties in compound 6. Quantum mechanical calculations on compound 6, performed by the AM1 method, predict that in its minimum energy conformation the TTF and TCNAQ moieties are approximately orthogonal to one another, with the TCNAQ unit folded into a butterfly conformation.
我们报告了利用官能化电子受体四氰基蒽醌二甲烷(TCNAQ)单元合成新型二元 DâÏ-A 化合物 6 和 7 [D=tetrathiafulvalenyl (TTF) and ferrocenyl] 以及三元 TTFâÏ-TCNAQâÏ-TTF 组合物 8 的情况。化合物 6â8 在紫外可见光谱中显示出非常微弱、宽广、低能的分子内电荷转移带。化合物 6 的纳秒激光闪烁光解并没有在 300â800 nm 区域产生任何新的瞬态吸收,这表明如果在激发时形成了电荷分离的物种,那么回电子转移就会非常迅速地发生,从而重新生成基态。化合物 6â8 的循环伏安法显示,TTF 和二茂铁分子发生了可逆的氧化过程,TCNAQ 分子发生了可逆的双电子还原。通过对化合物 6 的光谱电化学研究,可以确定氧化还原过程是 TTF 自由基阳离子和二阳离子在氧化时依次形成,TCNAQ 二阴离子在还原时依次形成。同时进行的电化学和 EPR(SEEPR)实验进一步证明了化合物 6 中 TTF 和 TCNAQ 分子之间的分子内相互作用。通过 AM1 方法对化合物 6 进行的量子力学计算预测,在其最小能量构象中,TTF 和 TCNAQ 分子近似相互正交,TCNAQ 单元折叠成蝶形构象。