Zhao Guohui, Chen Zongwei, Xiong Kao, Liang Guijie, Zhang Jianbing, Wu Kaifeng
State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China.
School of Optical and Electronic Information, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, China.
Nanoscale. 2021 Jan 21;13(2):1303-1310. doi: 10.1039/d0nr07837a.
Sensitization of molecular triplets using PbS quantum dots (QDs), followed by efficient triplet fusion, has been developed as a novel route to near-infrared-to-visible photon upconversion. Fundamentally, however, the mechanisms of triplet energy transfer (TET) from PbS QDs to surface-anchored polyacence acceptors remain highly debated. Here we study and side-by-side compare the kinetic pathways of TET from photoexcited PbS QDs to surface-anchored tetracene and pentacene derivatives using broad-band transient absorption spectroscopy spanning multiple decades of timescales. We find that the TET pathways are dictated by charge-transfer energetics at the QD/molecule interface. Charge transfer from QDs to tetracene was strongly endothermic, and hence spectroscopy showed one-step transformation from QD excited states to tetracene triplets in 302 ns. In contrast, hole transfer from QDs to pentacene was thermodynamically favoured and was confirmed by the formation of pentacene cation radicals in 13 ps, which subsequently evolved into pentacene triplets through a 101 ns electron transfer process. These results not only are consistent with a recently-established framework of charge-transfer-mediated TET, but also provide a route to manipulate triplet sensitization using lead-salt QDs for efficient upconversion of near-infrared photons.
利用硫化铅量子点（QDs）对分子三线态进行敏化，随后进行高效三线态融合，已被开发为一种实现近红外到可见光光子上转换的新途径。然而，从根本上讲，从硫化铅量子点到表面锚定的多并苯受体的三线态能量转移（TET）机制仍存在激烈争论。在这里，我们使用跨越多个时间尺度的宽带瞬态吸收光谱，研究并并排比较了从光激发的硫化铅量子点到表面锚定的并四苯和并五苯衍生物的TET动力学途径。我们发现，TET途径由量子点/分子界面处的电荷转移能量学决定。从量子点到并四苯的电荷转移强烈吸热，因此光谱显示在302纳秒内从量子点激发态到并四苯三线态的一步转变。相比之下，从量子点到并五苯的空穴转移在热力学上是有利的，并通过在13皮秒内形成并五苯阳离子自由基得到证实，该自由基随后通过101纳秒的电子转移过程演变成并五苯三线态。这些结果不仅与最近建立的电荷转移介导的TET框架一致，而且还提供了一条利用铅盐量子点操纵三线态敏化以实现近红外光子高效上转换的途径。
