Department of Chemistry & IRIS Adlershof, Humboldt-Universität zu Berlin , Brook-Taylor-Strasse 2, 12489 Berlin, Germany.
Theoretische Chemie, Institut für Chemie, Universität Potsdam , Karl-Liebknecht-Strasse 24-25, 14476 Potsdam-Golm, Germany.
J Am Chem Soc. 2017 Jan 11;139(1):335-341. doi: 10.1021/jacs.6b10822. Epub 2016 Dec 20.
A variety of azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo)switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization direction (Z → E) by the same wavelength of light, which normally triggers E → Z isomerization. The behavior we report appears to be general, implying that the metastable isomer of a photoswitch can be isomerized to the more stable one catalytically upon reduction, permitting the optimization of azobenzene switching in new as well as indirect ways.
合成了各种偶氮苯化合物，以研究其 E 和 Z 异构体在电化学还原过程中的行为。我们的结果表明，Z 异构体的自由基阴离子能够快速异构化为相应的 E 构型异构体，其速率明显高于中性物种。由于形成的 E 自由基阴离子随后向中性 Z 起始物质发生电子转移，整个转化过程在电子上是催化的；即，亚化学计量的还原物种可以异构化整个混合物。这种途径大大提高了（光）开关的效率，同时也允许人们达到不受单个偶氮苯异构体的光谱分离及其量子产率限制的光稳定态组成。此外，通过光电电子转移试剂激活这种自由基异构化途径，我们可以通过相同波长的光触发反向异构化方向（Z→E）来克服偶氮苯物种的固有性质，通常这会触发 E→Z 异构化。我们报道的行为似乎是普遍的，这意味着光开关的亚稳态异构体可以在还原时通过催化异构化为更稳定的异构体，从而以新的和间接的方式优化偶氮苯的开关。
