Photophysical Tuning of Imidazolium Tetrahalidomanganate(II) Complexes towards Highly Efficient Green Emitters with Near‐Unity Quantum Yield

• Published in: European journal of inorganic chemistry Vol. 27; no. 5
• Main Authors: Sääsk, Verner, Chen, Yi‐An, Huang, Tse‐Fu, Ting, Li‐Yu, Luo, Ting‐An, Fujii, Saki, Põhako‐Esko, Kaija, Yoshida, Masaki, Kato, Masako, Wu, Tien‐Lin, Chou, Ho‐Hsiu
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 12.02.2024
• Subjects: Bromine; Chlorine; Emitters; hybrid halides; light-emitting diodes; luminescence; Manganese; Photoluminescence; Room temperature; tetrahalidomanganates; transition metal complexes
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.202300562

Ten ionic manganese(II) complexes of [EMIm]2[MnX2Y2] (EMIm=1‐ethyl‐3‐methylimidazolium ion; X, Y=Cl, Br or I) and [BnMIm]2[MnX2Y2] (BnMIm=1‐benzyl‐3‐methylimidazolium ion; X, Y=Cl, Br or I) types were synthesized and studied in terms of their thermal and photophysical properties. Complexes with [BnMIm]+ cation were found to exhibit higher crystallinity, owing to the aromatic π‐stacking, and superior photoluminescent quantum yields, promoted by the increased Mn⋅⋅⋅Mn distance. For complexes with chlorine and bromine ligands efficient tunability of photophysical parameters was demonstrated. Out of all complexes, [BnMIm]2[MnBr4] was found to have the highest photoluminescence quantum yield at room temperature (Φ=0.59). To highlight the importance of a large Mn⋅⋅⋅Mn distance for achieving high Φ values, a mixed‐anion analog of complex [BnMIm]2[MnBr4] was prepared, with the suggested formula of [BnMIm]4[MnBr4]Br2. The latter have shown a significant improvement in d–d absorption efficiency and a reduction in nonradiative deactivation, which led to an outstanding Φ value of 0.97. Finally, the optical band gap of [BnMIm]4[MnBr4]Br2 was estimated to describe its applicability as light‐emitting material. A family of luminescent tetrahalidomanganate(II) complexes with imidazolium‐based cations were synthesized and characterized in detail. Their good thermal stability and photophysical tunability were demonstrated. In particular, [BnMIm]4[MnBr4]Br2, the complex with a novel mixed‐anion structure, showed exceptionally high photoluminescence quantum yield at room temperature, which suggests its future application as light‐emitting material in optoelectronic devices.