An Ultrafast Transient Absorption Study of Charge Separation and Recombination Dynamics in CdSe QDs and Methyl Viologen: Dependence on Surface Stoichiometry,ChemistrySelect

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An Ultrafast Transient Absorption Study of Charge Separation and Recombination Dynamics in CdSe QDs and Methyl Viologen: Dependence on Surface Stoichiometry
ChemistrySelect ( IF 1.9 ) Pub Date : 2018-03-06 , DOI: 10.1002/slct.201800313
M. Chandra Sekhar ₁ , Sneha Paul ₁ , Apurba De ₁ , Anunay Samanta ₁

Affiliation

The dependence of the dynamics of charge separation and recombination between methyl viologen (MV⁺²) and photo‐excited CdSe quantum dots (QDs) on the surface stoichiometry of the latter is studied for QDs with different Cd:Se mole ratios employing ultrafast time‐resolved absorption and emission measurements. The electron transfer rates between photoexcited CdSe QDs and MV⁺² are measured directly by monitoring the ultrafast rise and decay of the transient absorption signal due to methyl viologen monocationic radical (MV^+•). The results show that both forward and back electron transfer rates (5±1 x 10¹² s⁻¹ and 1.3±0.3 x 10¹⁰ s⁻¹, respectively) are independent of the stoichiometry of the QDs. Interestingly, the efficiency of the electron transfer process, estimated from the yield of MV^+•, shows significant dependence on the nature of the QDs, with maximum yield (Φ_rs=0.52±0.01) observed in the case of Cd‐rich QDs. These findings are explained considering the energetics and surface trap states of these systems.

中文翻译：

CdSe量子点和甲基紫精中电荷分离和复合动力学的超快速瞬态吸收研究：取决于表面化学计量

对于具有不同Cd：Se摩尔比的QD，研究了甲基紫精（MV ⁺²）和光激发的CdSe量子点（QDs）之间电荷分离和重组的动力学对后者的表面化学计量的依赖。解析的吸收和发射测量。通过监测由甲基紫精单阳离子基团（MV ^+•）引起的瞬态吸收信号的超快上升和衰减，可以直接测量光激发CdSe QD和MV ⁺²之间的电子传输速率。结果显示正向和反向电子传输速率（5±1 x 10 ¹² s ^-1和1.3±0.3 x 10 ¹⁰ s ^-1分别与QD的化学计量无关。有趣的是，根据MV ^+•的产率估算的电子转移过程的效率显示出对量子点性质的显着依赖性，对于富Cd量子点，其最大产率（_Φrs = 0.52±0.01）。考虑到这些系统的能量学和表面陷阱状态，对这些发现进行了解释。

更新日期：2018-03-06

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