Long-lived spin-triplet excitons in manganese complexes for room-temperature phosphorescence.

Abstract

Low-dimensional metal halide perovskites have become emerging candidates for applications in light emitting diodes due to the quantum confinement effect by tuning their composition and structure. However, they suffer from longstanding issues of environmental stability and lead toxicity. Herein, we report phosphorescent manganese halides, (TEM)2MnBr4 (TEM = HN(CH2CH3)3, triethylammonium) and (IM)6[MnBr4][MnBr6] (IM = C3H6N2, imidazolium) with a photoluminescence quantum yield (PLQY) of 50% and 7%, respectively. (TEM)2MnBr4 with a tetrahedral configuration exhibits brilliant green light emission centered at 528 nm, while the (IM)6[MnBr4][MnBr6] compound, in which octahedral and tetrahedral units coexist, exhibits red colored emission at 615 nm. The excited state of (TEM)2MnBr4 and (IM)6[MnBr4][MnBr6] is found to exhibit distinct photophysical emission characteristics consistent with triplet state phosphorescence. Efficient phosphorescence was achieved with a long lifetime of several milliseconds, 0.38 ms for (TEM)2MnBr4 and 5.54 ms for (IM)6[MnBr4][MnBr6], at room temperature. By studying the temperature dependent PL and single-crystal X-ray diffraction measurements and comparing our results with those of previously reported analogues, we have found a direct correlation between Mn⋯Mn distances and PL emission. Our study reveals that the long distance between the Mn centers has made a significant contribution to the long-lived phosphorescence with a highly emissive triplet state.