Delayed Dual Emission of Two-Dimensional Copper Nanocluster Assembly

Abstract

We report the formation of two-dimensional single crystalline nanosheets of Cu nanoclusters by complexation with Zn metal ion. The so-formed crystals, with augmented prompt photoluminescence and lifetime, exhibited delayed photoluminescence at room temperature with a quantum yield of 83.6 ± 1.3% and a lifetime of 26.4 ± 0.7 μs. The delayed photoluminescence lifetime was further increased to 145.0 ± 7.7 μs by surface functionalization of the nanosheets with 8-hydroxyquinoline. The surface complexation led to the generation of a new emitting channel in the crystal, which thus formed a single nanocomponent with dual channel emitting prompt and delayed near-white light.

Enhanced Chemical Stability in the Twisted Dodecagonal Stacking of Two-Dimensional Copper Nanocluster Assemblies

“…The as-synthesized CuNCs were then assembled into twodimensional structure of hexagonal symmetry via complexation reaction with Zn metal ion (∼21 mM) at the molar ratio of Cu:Zn of 1:21. 25 The Zn complexed CuNCs showed significant increment in photoluminescence intensity supporting the crystalline organization of the NCs (Figure S4A). The successful formation of the two-dimensional nanosheet (Figure S4B) exhibited a hexagonal diffraction pattern with lattice constant 4.7 ± 0.2 Å in the selected area electron diffraction pattern (SAED) analysis (Figure S4C).…”

“…The as-synthesized CuNCs were then assembled into two-dimensional structure of hexagonal symmetry via complexation reaction with Zn metal ion (∼21 mM) at the molar ratio of Cu:Zn of 1:21 . The Zn complexed CuNCs showed significant increment in photoluminescence intensity supporting the crystalline organization of the NCs (Figure S4A).…”

“…This was consistent with the proposed hexagonal structure of the Zn-CuNC nanosheets where CuNCs were proposed to be arranged in a continuous hexagonal pattern with one additional CuNC at the center of each hexagon. 25 Further details of structural bonding are presented later. The FTIR spectrum with significant shifts in carboxylate stretching frequencies also supported the probable bond formation between Zn and carboxylate groups of the ligands attached to the NCs (Figure S5).…”

“…22 Interestingly, in a recent work on the complexation of CuNCs with Zn 2+ ions that resulted in two-dimensional nanosheets, it was shown that the structures could further be functionalized with 8hydroxyquinoline, thereby suggesting the presence of Zn with unsaturated coordination on the surface. 25 The Journal of Physical Chemistry Letters However, it is also known that there were ligands bound to the NCs but not coordinated to the Zn in the hexagonal nanosheets. This would mean that it is plausible that two hexagonal nanosheets could again react with each other involving Zn 2+ ions on the surface of one nanosheet and the free ligands dangling from the surface nanoclusters of the other.…”

“…Copper nanoclusters (CuNCs) stabilized by mercaptopropanoic acid (MPA) and mercaptobenzoic acid (MBA) were synthesized according to a reported procedure . The red luminescent CuNCs with emission maximum at 615 nm did not exhibit any characteristic absorption peak of larger sized nanoparticles at 560 nm in the UV–vis spectrum (Figure S1).…”