From Blue to White to Yellow Emitter: A Hexanuclear Copper Iodide Nanocluster

Highly emissive copper(I) halide nanoclusters having thermally activated delayed fluorescence (TADF) have been paid much attention, but rarely reported so far. Here, a hexanuclear copper(I) iodide cluster containing tridentate N˄P˄N ligand, [Cu6I6(ppda)2] {ppda = 2-[2-(dimthylamino)phenyl(phenyl)phosphino]-N,N-dimethylaniline}, was synthesized. All six copper atoms are four-coordinate, including four CuPNI2 and two CuI4 units. This complex exhibits intense white emission in powder state at room temperature and has peak wavelength at 535 nm (ΦPL = 0.36) with microsecond lifetime (τ = 4.4 μs). Emission color can be largely tuned from blue to white to yellow, from crystal to powder to film state at 297 K. The emission of [Cu6I6(ppda)2] originates from a combination of MLCT and XLCT transitions. This complex displayed good thermal stability. A solution-processed, nondoped device of complex [Cu6I6(ppda)2] exhibits stable yellow emission with CIE(x,y) of (0.43, 0.51). [Cu6I6(ppda)2] also shows a reasonable photocatalytic H2 evolution activity under visible-light irradiation.