Surface States Mediate Triplet Energy Transfer in Nanocrystal-Acene Composite Systems
Surface States Mediate Triplet Energy Transfer in Nanocrystal-Acene Composite Systems
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DOI：
10.1021/jacs.8b01966
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发表时间：
2018-06-20
影响因子：
15
通讯作者：
Roberts, Sean T.
中科院分区：
文献类型：
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作者：
Bender, Jon A.;Raulerson, Emily K.;Roberts, Sean T.
杂化有机：无机材料是一种很有前途的光子上转换平台，它由半导体纳米晶和并苯配体组成。被纳米晶体吸收的红外光激发电荷载流子，这些载流子可以传递到表面结合的苯并茂，形成能够融合产生可见光辐射的三重态激子。要完全实现这一方案，必须高效地在纳米晶体和并苯之间进行能量转移，但这个过程的机理仍然知之甚少。为了提高我们对纳米粒子中涉及到的基本步骤：并苯能量传递的了解，我们使用超快瞬时吸收研究了6，13-双(三异丙基硅乙炔)并五苯(TIPS-五苯)配体化学官能化的PbS纳米晶的激发电子动力学。我们发现，PbS的光激发并不直接导致三重态能量转移到表面结合的TIPS-并五苯分子，而是在40ps内形成一个中间态。这种中间体持续大约100 ns，然后演化成尖端-并五苯三重态激子。对暂态吸收线形的分析表明，该中间体对应于PbS纳米晶表面的载流子。这一假设得到了约束DFT计算的支持，这些计算发现在PBS NC表面上存在大量的自旋三重态。虽然这些状态中的一些可以促进三胞胎的转移，但另一些状态则是阻碍三胞胎转移的陷阱。我们的结果强调了纳米晶表面在调节能量传递到束缚的ACEN配体中起着积极的作用，并且在优化用于光子上转换、光催化和其他光电子学应用的复合纳米材料时必须考虑到这一点。
Hybrid organic:inorganic materials composed of semiconductor nanocrystals functionalized with acene ligands have recently emerged as a promising platform for photon upconversion. Infrared light absorbed by a nanocrystal excites charge carriers that can pass to surface-bound acenes, forming triplet excitons capable of fusing to produce visible radiation. To fully realize this scheme, energy transfer between nanocrystals and acenes must occur with high efficiency, yet the mechanism of this process remains poorly understood. To improve our knowledge of the fundamental steps involved in nanoparticle:acene energy transfer, we used ultrafast transient absorption to investigate excited electronic dynamics of PbS nanocrystals chemically functionalized with 6,13-bis-(triisopropylsilylethynyl)pentacene (TIPS-pentacene) ligands. We find photoexcitation of PbS does not lead to direct triplet energy transfer to surface-bound TIPS-pentacene molecules but rather to the formation of an intermediate state within 40 ps. This intermediate persists for similar to 100 ns before evolving to produce TIPS-pentacene triplet excitons. Analysis of transient absorption lineshapes suggests this intermediate corresponds to charge carriers localized at the PbS nanocrystal surface. This hypothesis is supported by constrained DFT calculations that find a large number of spin-triplet states at PbS NC surfaces. Though some of these states can facilitate triplet transfer, others serve as traps that hinder it. Our results highlight that nanocrystal surfaces play an active role in mediating energy transfer to bound acene ligands and must be considered when optimizing composite NC-based materials for photon upconversion, photocatalysis, and other optoelectronic applications.