Unravelling the origin of dual photoluminescence in Au2Cu6 clusters by triplet sensitization and photon upconversion
Unravelling the origin of dual photoluminescence in Au2Cu6 clusters by triplet sensitization and photon upconversion
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通过三重态敏化和光子上转换揭示 Au2Cu6 团簇中双光致发光的起源
DOI：
10.1039/d1tc04591a
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发表时间：
2022
影响因子：
6.4
通讯作者：
Mitsui Masaaki
中科院分区：
文献类型：
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作者：
Arima Daichi;Niihori Yoshiki;Mitsui Masaaki
配体保护的贵金属簇合物由于其化学组成和结构的多样性，以及易于调节的单原子精度的电子和光物理性质，在发光材料和光敏剂方面具有很好的应用前景。许多研究表明，通过合金化金属核或增加配体环境的刚性可以显著提高这些团簇的光致发光(PL)性质。然而，它们的发光的基本性质(无论是荧光还是磷光)以及提高它们的发光的基本过程还没有完全阐明。在本研究中，我们确定了Au2Cu6(S-Adm)6(PPh_3)_2(S-Adm=1-金刚烷硫酸盐)簇合物在室温下不仅有荧光，而且有磷光。此外，我们发现Au2Cu6作为三重态增敏剂，通过对光子上转换现象的分析，我们确定了所有辐射和非辐射过程的速率常数和量子产额，这些过程涉及到团簇的激发单态和三态。荧光光谱的温度依赖关系和理论计算表明，热激活的系间交叉是通过高激发态(S2和/或T2)介导的自旋-振动耦合机制发生的，在这种机制下，直接的自旋-轨道耦合是可能的。
Ligand-protected, noble-metal clusters are promising as luminescent materials and photosensitizers because of their diverse chemical compositions and structures, as well as their easily tunable electronic and photophysical properties with single-atom precision. Many studies have shown that the photoluminescence (PL) properties of these clusters can be significantly enhanced by alloying the metal core or by increasing the rigidity of the ligand environment. However, the fundamental nature of their PL (whether fluorescent or phosphorescent) and the elementary process for enhancing their PL have not been fully clarified. In this study, we established that Au2Cu6(S-Adm)6(PPh3)2 (S-Adm = 1-adamantanethiolate) clusters exhibit not only fluorescence but also phosphorescence at room temperature. Further, we discovered that Au2Cu6 serves as a triplet sensitizer, and through the analysis of the photon-upconversion phenomenon, we determined the rate constants and quantum yields of all radiative and non-radiative processes involving the excited singlet and triplet states of the clusters. The temperature dependence of the PL and the theoretical calculations indicated that thermally activated intersystem crossing occurs through the spin–vibronic coupling mechanism mediated by higher excited states (S2 and/or T2) where direct spin–orbit coupling is possible.