Influence of Surface Ligands on Charge-Carrier Trapping and Relaxation in Water-Soluble CdSe@CdS Nanorods
Influence of Surface Ligands on Charge-Carrier Trapping and Relaxation in Water-Soluble CdSe@CdS Nanorods
复制标题
DOI：
10.3390/catal10101143
复制
发表时间：
2020-10-01
期刊：
影响因子：
3.9
通讯作者：
Wachtler, Maria
中科院分区：
文献类型：
--
作者：
Micheel, Mathias;Liu, Bei;Wachtler, Maria
在本研究中，密切研究了胶体CdSe@CdS棒中点纳米结构表面配体类型对基本激子弛豫和电荷局部化过程的影响。这些系统已被引入到人工光合作用领域，作为光驱动制氢组件的有效光敏剂。在光诱导激子产生后，电子可以转移到催化反应中心，而空穴则定位在CdSe种子中，这可以防止电荷重组，并导致在含有催化反应中心的组件中形成长寿命的电荷分离。这些过程与表面缺陷处电荷的捕获过程是竞争的。表面缺陷的密度和类型很大程度上取决于所使用的配体的类型。在这里，我们报告了一个系统的稳态和时间分辨光谱研究，研究了锚定基团（氧化膦、硫醇、二硫醇、胺）的类型和配体的体积（烷基链与聚乙二醇（PEG））的影响，以揭示捕获途径和定位效率。我们发现，与三辛基膦氧化物（TOPO）覆盖棒相比，广泛使用的硫醇配体的引入导致表面空穴陷阱的增加，这阻止了CdSe核心的空穴定位。另一方面，空间限制，例如在二硫酯中或具有大体积侧链（PEG）的空间限制，减少了表面覆盖率，增加了电子陷阱态的密度，影响了在ns时间尺度上的重组动力学。另一方面，聚乙烯亚胺（PEI）中的胺可以在很大程度上饱和和去除表面陷阱。讨论了催化的意义。
In this study, the impact of the type of ligand at the surface of colloidal CdSe@CdS dot-in-rod nanostructures on the basic exciton relaxation and charge localization processes is closely examined. These systems have been introduced into the field of artificial photosynthesis as potent photosensitizers in assemblies for light driven hydrogen generation. Following photoinduced exciton generation, electrons can be transferred to catalytic reaction centers while holes localize into the CdSe seed, which can prevent charge recombination and lead to the formation of long-lived charge separation in assemblies containing catalytic reaction centers. These processes are in competition with trapping processes of charges at surface defect sites. The density and type of surface defects strongly depend on the type of ligand used. Here we report on a systematic steady-state and time-resolved spectroscopic investigation of the impact of the type of anchoring group (phosphine oxide, thiols, dithiols, amines) and the bulkiness of the ligand (alkyl chains vs. poly(ethylene glycol) (PEG)) to unravel trapping pathways and localization efficiencies. We show that the introduction of the widely used thiol ligands leads to an increase of hole traps at the surface compared to trioctylphosphine oxide (TOPO) capped rods, which prevent hole localization in the CdSe core. On the other hand, steric restrictions, e.g., in dithiolates or with bulky side chains (PEG), decrease the surface coverage, and increase the density of electron trap states, impacting the recombination dynamics at the ns timescale. The amines in poly(ethylene imine) (PEI) on the other hand can saturate and remove surface traps to a wide extent. Implications for catalysis are discussed.