Sky Blue and Yellow Cluster Light-Emitting Diodes Based on Asymmetric Cu₄I₄ 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 Cu₄I₄ nanoclusters with asymmetric configurations, named [tBCzDBFDP]₂Cu₄I₄ and [PTZDBFDP]₂Cu₄I₄. Through changing 3,6-di-tert-butyl-carbazole (tBCz) to phenothiazine (PTZ) with a stronger electron-donating effect, emission color is tuned from greenish blue of [tBCzDBFDP]₂Cu₄I₄ to yellow of [PTZDBFDP]₂Cu₄I₄, 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]₂Cu₄I₄ is superior to [PTZDBFDP]₂Cu₄I₄, in accord with the stabilities of their triplet locally excited state and triplet charge transfer state. As a consequence, these asymmetric Cu₄I₄ 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.