Intercluster aurophilicity-driven aggregation lighting circularly polarized luminescence of chiral gold clusters
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Intercluster aurophilicity-driven aggregation lighting circularly polarized luminescence of chiral gold clusters Zhen Han§, Xueli Zhao§, Peng Peng, Si Li, Chong Zhang, Man Cao, Kai Li, Zhao-Yang Wang (), and Shuang-Quan Zang () Green Catalysis Center, and College of Chemistry, Zhengzhou University, Zhengzhou 450001, China § Zhen Han and Xueli Zhao contributed equally to this work. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 27 June 2020 / Revised: 18 July 2020 / Accepted: 20 July 2020
ABSTRACT Herein, we prepared two novel pairs of enantiomeric gold cluster complexes, Au4PL4/Au4PD4 and (Au4L4)n/(Au4D4)n with atomic precision. In Au4PL4/Au4PD4, the discrete chiral Au4-based aggregation-induced emission (AIE) luminogens are separated by bulky substitutes. The corresponding aggregates are cyan-emitting with a photoluminescence quantum yield (PLQY) of 14.4%. Upon decreasing the size of the substituents, these chiral Au4 clusters are strung together by inter-cluster Au–Au interactions, which cause a low-energy green emission from the aggregated (Au4L4)n/(Au4D4)n with a much higher PLQY of 41.4% and more intense circularly polarised photoluminescence (CPL) with a dissymmetry factor gPL of 7.0 × 10−3. Using (Au4L4)n/(Au4D4)n, circularly polarised organic light-emitting diodes (CP-OLEDs) were for the first time fabricated with gEL = gPL. These findings signify that inter-cluster metallophilic interactions are a new and important type of driving force for AIE and crystallization-induced emission (CIE), suggesting great potential of CPL-active metal clusters in CP-OLEDs.
KEYWORDS gold cluster, atomic precision, aggregation-induced emission, intercluster aurophilicity, circularly polarized luminescence
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Introduction
Ultrasmall luminescent gold clusters have very promising applications in imaging, sensing, and biological labelling [1–9]. Aggregation-induced emission (AIE) [10], crystallization-induced emission (CIE) [11] and clusterization-triggered emission (CTE) [12, 13] successfully explain the bright emission of aromatic chromophores and nonconjugated structures in aggregates or solid states respectively. Gold clusters have been studied for both AIE and CIE, which provide valuable insight into the underlying emission mechanism of metal clusters [11, 14, 15]. Xie’s group made significant contributions to the AIE of thiolated gold clusters in a discrete state [16–18]. Very recently, they managed to enhance the quantum yield (QY) to 6.2% by assembling ultrasmall gold nanoparticles into nanoribbons [19] via aurophilic interactions [20–22]. Yam’s group produced aggregates of Au(I) clusters under different solvent systems, which led to a change in the extent of Au(I)–Au(I) interactions [20–22] and, hence, variable luminescence [23]. Konish et al. reported the aggregation-induced fluorescence-tophosphorescence switching by intercluster aggregation of gold clusters [24]. However, there has been no substantial research on controlling atomically precise gold clus
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