Wu Yilei, Zhou Jiawang, Nelson Jordan N, Young Ryan M, Krzyaniak Matthew D, Wasielewski Michael R
Department of Chemistry and Institute for Sustainability and Energy , Northwestern Northwestern University , 2145 Sheridan Road , Evanston , Illinois 60208-3113 , United States.
J Am Chem Soc. 2018 Oct 10;140(40):13011-13021. doi: 10.1021/jacs.8b08105. Epub 2018 Sep 27.
Ultrafast photodriven electron transfer reactions starting from an excited singlet state in an organic donor-acceptor molecule generate a radical pair (RP) in which the two spins are initially entangled and, in principle, can serve as coupled spin qubits in quantum information science (QIS) applications, provided that spin coherence lifetimes in these RPs are long. Here we investigate the effects of electron transfer between two equivalent sites comprising the reduced acceptor of the RP. A covalent electron donor-acceptor molecule (D-C-A) including a p-methoxyaniline donor (D), a 4-aminonaphthalene-1,8-imide chromophoric primary acceptor (C), and a m-xylene bridged cyclophane having two equivalent phenyl-extended viologens (A) as a secondary acceptor was synthesized along with the analogous molecule having one phenyl-extended viologen acceptor and a second, more difficult to reduce 2,5-dimethoxyphenyl-extended viologen in a very similar cyclophane structure (D-C-A). Photoexcitation of C within each molecule results in subnanosecond formation of D-C-A and D-C-A. The spin dynamics of these RPs were characterized by time-resolved EPR spectroscopy and magnetic field effects on the RP yield in both CHCN and CDCN. The data show that rapid electron hopping within A promotes spin decoherence in D-C-A relative to D-C-A having a monomeric acceptor, while the interaction of the RP electron spins with the nuclear spins of the solvent have little or no effect on the spin dynamics. These observations provide important information for designing and understanding novel molecular assemblies of spin qubits with long coherence times for QIS applications.
在有机供体-受体分子中，从激发单重态开始的超快光驱动电子转移反应会产生一个自由基对（RP），其中两个自旋最初是纠缠的，并且原则上可以在量子信息科学（QIS）应用中用作耦合自旋量子比特，前提是这些RP中的自旋相干寿命足够长。在这里，我们研究了组成RP还原受体的两个等效位点之间电子转移的影响。合成了一种共价电子供体-受体分子（D-C-A），它包括对甲氧基苯胺供体（D）、4-氨基萘-1,8-二甲酰亚胺发色团主受体（C）以及具有两个等效苯基扩展紫精（A）作为二级受体的间二甲苯桥连环芳烷，同时还合成了具有非常相似环芳烷结构的类似分子，该分子具有一个苯基扩展紫精受体和第二个更难还原的2,5-二甲氧基苯基扩展紫精（D-C-A）。每个分子中C的光激发会在亚纳秒内形成D-C-A和D-C-A。通过时间分辨电子顺磁共振光谱以及在CHCN和CDCN中磁场对RP产率的影响来表征这些RP的自旋动力学。数据表明，相对于具有单体受体的D-C-A，A内的快速电子跳跃会促进D-C-A中的自旋退相干，而RP电子自旋与溶剂核自旋的相互作用对自旋动力学几乎没有影响。这些观察结果为设计和理解用于QIS应用的具有长相干时间的新型自旋量子比特分子组件提供了重要信息。
