Work

Iridium(III) Carbene Complexes Featuring Either Metal‐to‐Ligand Charge Transfer (MLCT) or Through‐Space Charge Transfer (TSCT) Blue Luminescence

Year: 2025

Type: article

Abstract: Through‐space charge transfer (TSCT), rather than the commonly postulated metal‐to‐ligand charge transfer (MLCT) process, was proposed in getting the lowest lying excited state of newly designed Ir(III) blue phosphors. Accordingly, two benzo[d]imidazolylidene pro‐chelates, L12H2+ and L13H2+, one with two cyano groups at the peri‐benzo and N‐aryl pendent and the other with its peri‐cyano group being replaced with methyl substituent, were employed in syntheses of Ir(III) complexes f‐ct12b,c and f‐ct13b,c. Notably, complexes f‐ct12b,c exhibited the traditional MLCT process, while f‐ct13b,c were dominated by the TSCT transition, resulting in a smaller S1–T1 energy gap ΔEST. Next, it prompted us to explore whether their long‐lived emission originated from phosphorescence or thermally activated delayed fluorescence (TADF). Although temperature‐dependent emission studies favor TADF, the unresolved concerns are still discussed in depth. For application, OLED with the TSCT‐based dopant f‐ct13b delivered a maximum external quantum efficiency (EQE) of 22.2% and a max. luminance of 10 000 cd m‒2, together with CIExy of (0.155, 0.120). Moreover, the hyper‐OLED with f‐ct13c sensitizer and v‐DABNA terminal emitter exhibited a max. EQE of 28.2% and CIExy of (0.123, 0.129), demonstrating a new approach in developing efficient Ir(III) blue phosphors.

Source: Angewandte Chemie

DOI: 10.1002/ange.202424694