From a blue to white to yellow emitter: a hexanuclear copper iodide nanocluster.

Highly emissive copper(i) halide nanoclusters showing thermally activated delayed fluorescence (TADF) have been paid much attention, but rarely reported so far. Herein, a hexanuclear copper(i) iodide cluster containing a tridentate N∧P∧N ligand, [Cu6I6(ppda)2] {ppda = 2-[2-(dimethylamino)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 the powder state at room temperature and shows a peak at a wavelength of 535 nm (ΦPL = 0.36) with a microsecond lifetime (τ = 4.4 μs). Emission colors can be largely tuned from blue to white to yellow, from the 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 showed good thermal stability. A solution-processed, nondoped device of complex [Cu6I6(ppda)2] exhibits stable yellow emission with the CIE coordinates (x, y) of (0.43, 0.51). [Cu6I6(ppda)2] also shows reasonable photocatalytic H2 evolution activity under visible-light irradiation.