Highly emissive 4-carbazole-appended salen-indium complex: the effect of strong donor-acceptor interaction

Herein, we report our findings on 4-carbazole (CBZ)-appended salen-based indium complexes, CBZIn1 and CBZIn2, which feature diimine bridges exhibiting different electron-accepting properties. Notably, CBZIn2 exhibited a significantly higher photoluminescence quantum efficiency (PLQY, & phi;PL) in toluene than CBZIn1, with a value over 15 times greater (& phi;PL = 57.7% for CBZIn2; & phi;PL = 3.7% for CBZIn1). In particular, in the rigid state of THF at 77 K, CBZIn2 exhibited a near-unity PLQY of 98.2%. Even in the PMMA film, CBZIn2 maintained a high level of PLQY (& phi;PL = 70.2%). These results can be attributed to the highly efficient radiative decay process based on intramolecular charge-transfer (ICT) transition between the moderately twisted CBZ, characterized by its conformational rigidity and the 1,2-dicyanoethylene-bridged salen, which exhibits a strong electron-accepting ability. Furthermore, these findings are supported by theoretical calculations. The paper presents a highly photoluminescent 4-CBZ-appended indium-based complex in THF at 77 K (& phi;PL = 98.2%) and PMMA film (& phi;PL = 70.2%). These results were obtained by the formation of an efficient D-A interaction.

Automated summary

In this study, we investigated 4-carbazole (CBZ)-appended salen-based indium complexes, CBZIn1 and CBZIn2. Our findings revealed that CBZIn2 exhibited significantly higher photoluminescence quantum efficiency in toluene compared to CBZIn1. The high efficiency of CBZIn2 can be attributed to the intramolecular charge-transfer transition between the moderately twisted CBZ and the 1,2-dicyanoethylene-bridged salen, which exhibits a strong electron-accepting ability. These results were supported by theoretical calculations.