Department of Chemistry, College of Science, Rikkyo University, 3-34-1, Nishiikebukuro, Toshima-ku, Tokyo 171-8501, Japan.
J Am Chem Soc. 2023 Mar 29;145(12):6994-7004. doi: 10.1021/jacs.3c00870. Epub 2023 Mar 20.
Ligand-protected noble-metal nanoclusters exhibit an innately triplet nature and have been recently recognized as emerging platforms for triplet sensitizers of photon upconversion (UC) via triplet-triplet annihilation. Herein, we report that a structurally flexible Au-Cu alloy nanocluster, [AuCu(S-Adm)(DPPM)] (; S-Adm = 1-adamantanethiolate, DPPM = bis(diphenylphosphino)methane), exhibited favorable sensitizer properties and superior UC performance. Contrary to the structurally rigid AuCu(S-Adm)(TPP) (, TPP = triphenylphosphine), exhibited significantly better sensitizer characteristics, such as a near-unity quantum yield for intersystem crossing (ISC), long triplet lifetime (ca. 8 μs), and efficient triplet energy transfer (TET). The efficient ISC of was attributed to the practically negligible activation barriers during the ISC process, which was caused by the spin-orbit interaction between the two isoenergetic isomers predicted by theoretical calculations. A series of aromatic molecules with different triplet energies were used as acceptors to reveal the driving force dependence of the TET rate constant (). This dependency was analyzed to evaluate the triplet energy and sensitization ability of the alloy nanoclusters. The results showed that the maximum value of for was seven times larger than that for , which presumably reflects the structural/electronic fluctuations of during the triplet state residence. The combination of the sensitizer and the 9,10-diphenylanthracene (DPA) annihilator/emitter achieved UC with internal quantum yields of 14% (out of 50% maximum) and extremely low threshold intensities (2-26 mWcm). This performance far exceeds that of and is also outstanding among the organic-inorganic hybrid nanomaterials reported so far.
配体保护的贵金属纳米团簇表现出固有三重态性质，最近被认为是通过三重态-三重态湮灭的光子上转换（UC）三重态敏化剂的新兴平台。在此，我们报告了一种结构灵活的 Au-Cu 合金纳米团簇，[AuCu(S-Adm)(DPPM)]（; S-Adm = 1-金刚烷硫醇，DPPM = 双（二苯基膦）甲烷），表现出良好的敏化剂特性和优异的 UC 性能。与结构刚性的 AuCu(S-Adm)(TPP)（，TPP = 三苯基膦）相比，[AuCu(S-Adm)(DPPM)]表现出明显更好的敏化剂特性，例如近乎完美的系间窜越（ISC）量子产率、长三重态寿命（约 8 μs）和有效的三重态能量转移（TET）。ISC 的高效性归因于理论计算预测的两个等能异构体之间的自旋轨道相互作用，导致ISC 过程中几乎可以忽略不计的活化能垒。一系列具有不同三重态能量的芳香族分子被用作受体，以揭示 TET 速率常数（）的驱动力依赖性。对该依赖性进行了分析，以评估合金纳米团簇的三重态能量和敏化能力。结果表明，对于[AuCu(S-Adm)(DPPM)]，的最大值是对于[AuCu(S-Adm)(TPP)]的七倍，这可能反映了三重态停留期间的结构/电子波动。敏化剂和 9,10-二苯基蒽（DPA）湮灭剂/发射器的组合实现了内部量子效率为 14%（50%最大值）和极低的阈值强度（2-26 mWcm）的 UC。这种性能远远超过了[AuCu(S-Adm)(TPP)]，并且在迄今为止报道的有机-无机杂化纳米材料中也是杰出的。
