Sky Blue and Yellow Cluster Light-Emitting Diodes Based on Asymmetric Cu ₄ I ₄ Nanocubes

Abstract

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 Cu 4 I 4 nanoclusters with asymmetric configurations, named [tBCzDBFDP] 2 Cu 4 I 4 and [PTZDBFDP] 2 Cu 4 I 4 . 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] 2 Cu 4 I 4 to yellow of [PTZDBFDP] 2 Cu 4 I 4 , 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] 2 Cu 4 I 4 is superior to [PTZDBFDP] 2 Cu 4 I 4 , in accord with the stabilities of their triplet locally excited state and triplet charge transfer state. As a consequence, these asymmetric Cu 4 I 4 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.

Electroluminescent Clusters

“…Phenothiazine (PTZ) with stronger electron donating effect made emission of 25 shifted to orange, whose devices also achieved a favourable EQE reaching 8.6 %. [41] Acridine groups with appropriate electron-donating effect and orthogonal configurations were used to form two mono-substituted DBFDP ligands and corresponding Cu 4 I 4 cubes 26 and 27 with bluish-green TADF. [42] Accelerated singlet radiation and reduced triplet quenching gave rise to their PLQYs reaching 73 % and 81 % for 26 and 27, respectively.…”

“…Cationic Ag 6 Cu-based heteronuclear clusters (41) were stablized with CH(PPh 2 ) 3 and ethynyl ligands, whose PH was attributed to 3 [d!s/p] and 3 LLCT. [50] Based on electronic effects of substituents, the emission color and carrier transportation can be modified to support the maximum EQE reaching 13.9 %.…”

“…Mono‐functionalization of DBFDP with tBCz can further alleviate interaction induced quenching of 24 , in addition to limiting 3 CC population, rendering a higher EQE of 12.2 % for its sky blue devices. Phenothiazine (PTZ) with stronger electron donating effect made emission of 25 shifted to orange, whose devices also achieved a favourable EQE reaching 8.6 % [41] …”

Ligand-mediate exciton allocation enables efficient cluster-based white light-emitting diodes via single and heavy doping

“…In recent years, on the basis of ligand engineering, we developed a series of bluish green EL Cu 4 I 4 cubic clusters with the state-of-the-art η EQE beyond 20% 39 – 42 . Nonetheless, despite a single-molecular white-emitting Cu 4 I 4 cluster also demonstrated 43 , there are no white cluster light-emitting devices (CLED) reported until present, since the maximum η EQE of yellow emissive Cu 4 I 4 cubes was still less than 10% 44 . The previous works showed that donor modification can enhance LC components, reduce bandgaps and increase molecular polarity.…”

Efficient doped and non-doped light-emitting diodes based on a TADF-emitting Cu4Br4 cluster

“…26,27 In addition, a substantial number of copper(I)halide clusters are insoluble in conventional solvents and exhibit instability during sublimation, which makes them unsuitable for fabricating cluster light-emitting diodes (CLEDs) via solution-based processes and vacuum deposition. Despite some progress, 10,[28][29][30][31][32][33][34][35] the rational design of copper(I)halide clusters for highly efficient CLEDs and the comprehension of structure-property relationships continue to pose challenges.…”