van Turnhout Lars, Congrave Daniel G, Yu Zhongzheng, Arul Rakesh, Dowland Simon A, Sebastian Ebin, Jiang Zhao, Bronstein Hugo, Rao Akshay
Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom.
J Am Chem Soc. 2024 Aug 14;146(32):22612-22621. doi: 10.1021/jacs.4c07004. Epub 2024 Aug 5.
Lanthanide-doped nanoparticles (LnNPs) possess unique optical properties and are employed in various optoelectronic and bioimaging applications. One fundamental limitation of LnNPs is their low absorption cross-section. This hurdle can be overcome through surface modification with organic chromophores with large absorption cross-sections. Controlling energy transfer from organic molecules to LnNPs is crucial for creating optically bright systems, yet the mechanisms are not well understood. Using pump-probe spectroscopy, we follow singlet energy transfer (SET) and triplet energy transfer (TET) in systems comprising different length 9,10-bis(phenylethynyl)anthracene (BPEA) derivatives coordinated onto ytterbium and neodymium-doped nanoparticles. Photoexcitation of the ligands forms singlet excitons, some of which convert to triplet excitons via intersystem crossing when coordinated to the LnNPs. The triplet generation rate and yield are strongly distance-dependent. Following their generation, TET occurs from the ligands to the LnNPs, exhibiting an exponential distance dependence, independent of solvent polarity, suggesting a concerted Dexter-type process with a damping coefficient of 0.60 Å. Nevertheless, TET occurs with near-unity efficiency for all BPEA derivatives due to the lack of other triplet deactivation pathways and long intrinsic triplet lifetimes. Thus, we find that close coupling is primarily important to ensure efficient triplet generation rather than efficient TET. Although SET is faster, we find its efficiency to be lower and more strongly distance-dependent than the TET efficiency. Our results present the first direct distance-dependent energy transfer measurements in LnNP@organic nanohybrids and establish the advantage of using the triplet manifold to achieve the most efficient energy transfer and best sensitization of LnNPs with π-conjugated ligands.
镧系元素掺杂纳米粒子（LnNPs）具有独特的光学性质，被应用于各种光电子和生物成像领域。LnNPs的一个基本限制是其低吸收截面。通过用具有大吸收截面的有机发色团进行表面修饰可以克服这一障碍。控制从有机分子到LnNPs的能量转移对于创建光学明亮系统至关重要，但其机制尚未完全理解。我们使用泵浦 - 探测光谱法，研究了由不同长度的9,10 - 双（苯乙炔基）蒽（BPEA）衍生物配位到镱和钕掺杂纳米粒子上组成的系统中的单线态能量转移（SET）和三线态能量转移（TET）。配体的光激发形成单线态激子，其中一些在与LnNPs配位时通过系间窜越转化为三线态激子。三线态产生速率和产率强烈依赖于距离。三线态激子产生后，TET从配体发生到LnNPs，呈现指数距离依赖性，与溶剂极性无关，表明这是一个具有0.60 Å阻尼系数的协同德克斯特型过程。然而，由于缺乏其他三线态失活途径和长的固有三线态寿命，所有BPEA衍生物的TET效率几乎都达到了单位效率。因此，我们发现紧密耦合对于确保高效的三线态产生而非高效的TET至关重要。尽管SET更快，但我们发现其效率比TET效率更低且对距离更敏感。我们的结果首次展示了LnNP@有机纳米杂化物中直接的距离依赖性能量转移测量，并确立了利用三线态能级实现最有效的能量转移以及用π共轭配体对LnNPs进行最佳敏化的优势。
