Aruda Kenneth O, Amin Victor A, Thompson Christopher M, Lau Bryan, Nepomnyashchii Alexander B, Weiss Emily A
Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.
Langmuir. 2016 Apr 12;32(14):3354-64. doi: 10.1021/acs.langmuir.6b00689. Epub 2016 Mar 30.
This work describes the quantitative characterization of the interfacial chemical and electronic structure of CdSe quantum dots (QDs) coated in one of five p-substituted thiophenolates (X-TP, X = NH2, CH3O, CH3, Cl, or NO2), and the dependence of this structure on the p-substituent X. (1)H NMR spectra of mixtures of CdSe QDs and X-TPs yield the number of X-TPs bound to the surface of each QD. The binding data, in combination with the shift in the energy of the first excitonic peak of the QDs as a function of the surface coverage of X-TP and Raman and NMR analysis of the mixtures, indicate that X-TP binds to CdSe QDs in at least three modes, two modes that are responsible for exciton delocalization and a third mode that does not affect the excitonic energy. The first two modes involve displacement of OPA from the QD core, whereas the third mode forms cadmium-thiophenolate complexes that are not electronically coupled to the QD core. Fits to the data using the dual-mode binding model also yield the values of Δr1, the average radius of exciton delocalization due to binding of the X-TP in modes 1 and 2. A 3D parametrized particle-in-a-sphere model enables the conversion of the measured value of Δr1 for each X-TP to the height of the potential barrier that the ligand presents for tunneling of excitonic hole into the interfacial region. The height of this barrier increases from 0.3 to 0.9 eV as the substituent, X, becomes more electron-withdrawing.
这项工作描述了包覆在五种对取代苯硫酚盐（X-TP，X = NH₂、CH₃O、CH₃、Cl或NO₂）之一中的CdSe量子点（QD）的界面化学和电子结构的定量表征，以及这种结构对p-取代基X的依赖性。CdSe量子点与X-TP混合物的¹H NMR光谱得出了结合到每个量子点表面的X-TP的数量。结合数据，再加上量子点的第一个激子峰能量随X-TP表面覆盖率的变化以及混合物的拉曼光谱和NMR分析，表明X-TP以至少三种模式与CdSe量子点结合，其中两种模式负责激子离域，第三种模式不影响激子能量。前两种模式涉及邻苯二胺（OPA）从量子点核心的位移，而第三种模式形成与量子点核心没有电子耦合的镉-苯硫酚盐配合物。使用双模结合模型对数据进行拟合还得出了Δr1的值，即由于X-TP在模式1和2中的结合而导致的激子离域的平均半径。一个三维参数化球中粒子模型能够将每个X-TP的Δr1测量值转换为配体对激子空穴隧穿进入界面区域所呈现的势垒高度。随着取代基X的吸电子性增强，这个势垒的高度从0.3 eV增加到0.9 eV。
