Charge separation distance for flexible donor-bridge-acceptor systems after electron-transfer quenching.
Charge separation distance for flexible donor-bridge-acceptor systems after electron-transfer quenching.
复制标题
电子转移淬灭后柔性供体-桥-受体系统的电荷分离距离。
DOI：
10.1021/jp800396d
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
C. Braun
中科院分区：
文献类型：
--
作者：
Jinwei Zhou;L. V. Lukin;C. Braun
用光致瞬变偶极子实验测量了柔性电子给体/受体体系的有效电荷分离距离D-(CH2)n-A(其中D为4-N，N-二甲基苯胺，A为9-苯基，n=3，4，n=3，4)，相当于电子给体/受体柔性体系的光致偶极矩变化。对于n=4的化合物(DBA4)，偶极信号分析表明，在甲苯、1，4-二氧六环、乙酸乙酯、四氢呋喃、二氯甲烷、1，2-二氯乙烷、2-甲基戊酮-3，3-戊酮和苯甲腈中的有效电荷分离距离分别为2.2、2.5、4.5、4.7、5.5、5.5、4.8和6.3A。这些值可以理解为不同溶剂溶液中的均方根电荷分离距离。我们假设折叠接触构型的分离距离为3.5A，扩展的溶剂分离构型的分离距离为8.0A，并且它们是电子转移猝灭后仅有的两个稳定物种。估算了接触自由基离子对(CRIP)和溶剂分离自由基离子对(SSRIP)在不同溶剂中的形成效率。结果表明，当溶剂的介电常数大于10时，相当一部分离子对以溶剂分离离子对的形式存在。这些结果表明，在极性溶剂中，电子转移猝灭确实可以发生在大分离的情况下。它们还揭示了在大间隔时形成的离子对的势垒，阻碍了崩塌到大约3.5A的接触间隔。
Photoinduced transient dipole experiments are used to measure the effective charge separation distance, which is equivalent to the photoinduced change in dipole moment divided by the electron charge of flexible electron-donor/acceptor systems, D-(CH2)n-A, where D is 4- N,N-dimethylaniline, A is 9-anthryl, and n = 3, 4. We find that the dipole moments increase strongly with solvent polarity. For the compound with n = 4 (DBA4), analysis of dipole signals indicates that the effective charge separation distances in toluene, 1,4-dioxane, ethyl acetate, tetrahydrofuran, dichloromethane, 1,2-dichloroethane, 2-methylpentanone-3, 3-pentanone, and benzonitrile are 2.2, 2.5, 4.5, 4.7, 5.5, 5.5, 4.8, and 6.3 A, respectively. These values can be understood as the root-mean-square charge separation distance in the solutions of different solvents. We assume that the folded contact configuration has a separation distance of 3.5 A, the extended, solvent-separated configuration has a separation distance of 8.0 A, and that they are the only two stable species after electron-transfer quenching. The formation efficiencies of contact radical ion pairs (CRIPs) and solvent-separated radical ion pairs (SSRIPs) are estimated in different solvents. The results indicate that a significant fraction of the ion pairs exist as solvent-separated ion pairs when the dielectric constant of the solvent is larger than 10. These results indicate that electron-transfer quenching can indeed happen at large separations in polar solvents. They also reveal that there is a barrier for ion pairs formed at large separations, hindering collapse to a contact separation of around 3.5 A.