Excited-State Charge Transfer and Extended Charge Separation within Covalently Tethered Type-II CdSe/CdTe Quantum Dot Heterostructures: Colloidal and Multilayered Systems.
Excited-State Charge Transfer and Extended Charge Separation within Covalently Tethered Type-II CdSe/CdTe Quantum Dot Heterostructures: Colloidal and Multilayered Systems.
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DOI：
10.1021/acsami.1c05653
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发表时间：
2021-06
影响因子：
9.5
通讯作者：
Caitlin R. McGranahan;G. E. Wolfe;Alejandro Falca;David F. Watson
中科院分区：
文献类型：
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作者：
Caitlin R. McGranahan;G. E. Wolfe;Alejandro Falca;David F. Watson
我们使用N，N'-二环己基碳二亚胺（DCC）偶联化学来合成（1）在胶体分散体中的CdSe和CdTe量子点（QDs）的异质结构和（2）在金属氧化物薄膜上固定的CdSe和CdTe QDs以及CdS和CdSe QDs的异质结构。DCC介导的酰胺键的形成之间的末端羧酸和不同的量子点上的配体的胺基驱动异质结构的形成。这种交联机制选择性地产生异质结构，并阻止不期望的形成仅由一种类型的QD组成的同质结构。通过透射电子显微镜、ATR-FTIR、1H NMR、电子吸收、稳态发射和时间分辨发射光谱对吸附、配体交换和共价偶联反应的产物进行了表征。组成量子点的基态吸收光谱未受干扰纳入异质结构，使电子性质的控制。异质结构的CdSe和CdTe量子点表现出II型界面能量偏移，促进电荷分离激发后的量子点。事实上，光激发的CdTe量子点转移电子到CdSe，和光激发的CdSe量子点转移空穴到CdTe，在10 - 100 ns的时间尺度上，证明了带边和陷阱态发射的动态淬火。非相互作用量子点的混合分散体没有进行激发态电荷转移。在TiO2薄膜上构建异质结构引入了一个额外的电荷转移途径，即从量子点到TiO2的电子转移，它发生在亚纳秒的时间尺度上，并使光生电子和空穴的空间分离得以扩展。我们的研究结果表明，碳二亚胺耦合化学可用于拴胶体量子点选择性和共价相互，产生分散或固定的异质结构与可编程的组合物和能量偏移，可以进行有效的激发态界面电子转移。
We used N,N'-dicyclohexylcarbodiimide (DCC) coupling chemistry to synthesize (1) heterostructures of CdSe and CdTe quantum dots (QDs) in colloidal dispersions and (2) heterostructures of CdSe and CdTe QDs, as well as CdS and CdSe QDs, immobilized on metal oxide thin films. The DCC-mediated formation of amide bonds between terminal carboxylic acid and amine groups of ligands on different QDs drove the formation of heterostructures. This cross-linking mechanism selectively yields heterostructures and prohibits the undesired formation of homostructures consisting of just one type of QD. Products of adsorption, ligand-exchange, and covalent-coupling reactions were characterized by transmission electron microscopy and ATR-FTIR, 1H NMR, electronic absorption, steady-state emission, and time-resolved emission spectroscopy. Ground-state absorption spectra of constituent QDs were unperturbed upon incorporation into heterostructures, enabling control over electronic properties. Heterostructures of CdSe and CdTe QDs exhibit type-II interfacial energetic offsets that promote charge separation following excitation of either QD. Indeed, photoexcited CdTe QDs transferred electrons to CdSe, and photoexcited CdSe QDs transferred holes to CdTe, on time scales of 10-100 ns, as evidenced by dynamic quenching of band-edge and trap-state emission. Mixed dispersions of noninteracting QDs did not undergo excited-state charge transfer. Constructing heterostructures on TiO2 thin films introduced an additional charge-transfer pathway, electron transfer from QDs to TiO2, which occurred on subnanosecond time scales and enabled extended spatial separation of photogenerated electrons and holes. Our results reveal that carbodiimide coupling chemistry can be used to tether colloidal QDs selectively and covalently to each other, yielding dispersed or immobilized heterostructures with programmable compositions and energetic offsets that can undergo efficient excited-state interfacial electron transfer.