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

Abstract Ten ionic manganese(II) complexes of [EMIm] 2 [Mn X 2 Y 2 ] (EMIm=1‐ethyl‐3‐methylimidazolium ion; X , Y =Cl, Br or I) and [BnMIm] 2 [Mn X 2 Y 2 ] (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 [MnBr 4 ] 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 [MnBr 4 ] was prepared, with the suggested formula of [BnMIm] 4 [MnBr 4 ]Br 2 . 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 [MnBr 4 ]Br 2 was estimated to describe its applicability as light‐emitting material.