Xiang Bo, Li Yingmin, Pham C Huy, Paesani Francesco, Xiong Wei
Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093-0418, USA.
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0358, USA.
Sci Adv. 2017 Nov 17;3(11):e1701508. doi: 10.1126/sciadv.1701508. eCollection 2017 Nov.
The ability to control direct electron transfer can facilitate the development of new molecular electronics, light-harvesting materials, and photocatalysis. However, control of direct electron transfer has been rarely reported, and the molecular conformation-electron dynamics relationships remain unclear. We describe direct electron transfer at buried interfaces between an organic polymer semiconductor film and a gold substrate by observing the first dynamical electric field-induced vibrational sum frequency generation (VSFG). In transient electric field-induced VSFG measurements on this system, we observe dynamical responses (<150 fs) that depend on photon energy and polarization, demonstrating that electrons are directly transferred from the Fermi level of gold to the lowest unoccupied molecular orbital of organic semiconductor. Transient spectra further reveal that, although the interfaces are prepared without deliberate alignment control, a subensemble of surface molecules can adopt conformations for direct electron transfer. Density functional theory calculations support the experimental results and ascribe the observed electron transfer to a flat-lying polymer configuration in which electronic orbitals are found to be delocalized across the interface. The present observation of direct electron transfer at complex interfaces and the insights gained into the relationship between molecular conformations and electron dynamics will have implications for implementing novel direct electron transfer in energy materials.
控制直接电子转移的能力有助于新型分子电子学、光捕获材料和光催化的发展。然而，关于直接电子转移的控制鲜有报道，分子构象与电子动力学之间的关系仍不明确。我们通过观察首个动态电场诱导振动和频产生（VSFG），描述了有机聚合物半导体薄膜与金基底之间埋藏界面处的直接电子转移。在对该系统进行的瞬态电场诱导VSFG测量中，我们观察到了依赖于光子能量和偏振的动态响应（<150飞秒），这表明电子直接从金的费米能级转移到有机半导体的最低未占据分子轨道。瞬态光谱进一步揭示，尽管界面制备时没有进行刻意的取向控制，但表面分子的一个子集合能够采用有利于直接电子转移的构象。密度泛函理论计算支持了实验结果，并将观察到的电子转移归因于平躺的聚合物构型，其中电子轨道在界面上是离域的。目前在复杂界面处对直接电子转移的观察以及对分子构象与电子动力学之间关系的深入理解，将对在能量材料中实现新型直接电子转移具有重要意义。
