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[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.

Supramolecular crystals of Mn(15-crown-5)(MnCl4)(DMF) with dielectric phase transition, high quantum yield and phase transition-induced luminescence enhancement behavior

“…1 However, intense optical absorption or emission, corresponding to spin–forbidden transitions between the sextet ground state and upper quartet/doublet levels of the Mn 2+ ion, has been observed in various hosts and complexes so far. 2–11 Notably, in some cases, the photoluminescence (PL) yield of Mn 2+ complexes/organic–inorganic hybrids is near 100% at ambient temperature, 12–14 and the mechanisms may be related to effects such as low-symmetry ligand fields, 15 odd-parity vibrations, 16 charge-transfer states, 17 spin–orbit interactions, 18 and magnetic interactions. 19…”