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

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 pi-stacking, and superior photoluminescent quantum yields, promoted by the increased Mn & sdot;& sdot;& sdot;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 (phi=0.59). To highlight the importance of a large Mn & sdot;& sdot;& sdot;Mn distance for achieving high phi values, a mixed-anion analog of complex [BnMIm](2)[MnBr4] was prepared, with the suggested formula of [BnMIm](4)[MnBr4]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 phi value of 0.97. Finally, the optical band gap of [BnMIm](4)[MnBr4]Br-2 was estimated to describe its applicability as light-emitting material.

Automated summary

This study synthesized and investigated ten ionic manganese(II) complexes in terms of their thermal and photophysical properties. It was found that the complexes with the [BnMIm]+ cation exhibited higher crystallinity and superior photoluminescent quantum yields. Additionally, efficient tunability of photophysical parameters was demonstrated in complexes with chlorine and bromine ligands.