Sky Blue and Yellow Cluster Light-Emitting Diodes Based on Asymmetric CuI Nanocubes.

Controllably optimizing excited-state characteristics is crucial for luminescent nanoclusters but remains a formidable challenge. Herein, we report an effective "ligand-induced asymmetrization" strategy for constructing thermally activated delayed fluorescence-featured cubic CuI nanoclusters with asymmetric configurations, named [tBCzDBFDP]CuI and [PTZDBFDP]CuI. Through changing 3,6-di--butyl-carbazole (tBCz) to phenothiazine (PTZ) with a stronger electron-donating effect, emission color is tuned from greenish blue of [tBCzDBFDP]CuI to yellow of [PTZDBFDP]CuI, as well as the triplet locally excited state of the former to the triplet charge transfer state of the latter. Temperature-correlated spectroscopic investigation indicates that in terms of triplet quenching suppression, [tBCzDBFDP]CuI is superior to [PTZDBFDP]CuI, in accord with the stabilities of their triplet locally excited state and triplet charge transfer state. As a consequence, these asymmetric CuI nanocubes endowed their cluster light-emitting diodes with the external quantum efficiencies beyond 12% for sky blue and 8% for yellow. These results suggest the significance and effectiveness of ligand engineering for optoelectronic nanoclusters.