Structural\nDesign of Hybrid Manganese(II) Halides\nfor High Quantum Efficiency and Specific Response to Methanol

Manganese(II) halides have been a new generation of optoelectronic\nmaterials due to their fascinating luminescent properties, however,\nlacking specific solvent-responsive analogues with high quantum efficiency.\nHerein, we prepared three single crystals, [Pr(MIm)<sub>2</sub>][MnBr<sub>4</sub>] ([Pr(MIm)<sub>2</sub>]<sup>2+</sup> = 1,3-di(methylimidazolium)-propane, <b>Compound 1</b>), [Pr(EIm)<sub>2</sub>][MnBr<sub>4</sub>] ([Pr(EIm)<sub>2</sub>]<sup>2+</sup> = 1,3-di(ethylimidazolium)-propane, <b>Compound\n2</b>), and [Bu(MIm)<sub>2</sub>][MnBr<sub>4</sub>] ([Bu(MIm)<sub>2</sub>]<sup>2+</sup> = 1,4-di(methylimidazolium)-butane, <b>Compound\n3</b>), where different Bola-type cations were chosen as organic\ncomponents to separate [MnBr<sub>4</sub>]<sup>2–</sup> tetrahedrons.\nAll three compounds emitted bright green light with excellent quantum\nyields of 95.3, 80.0, and 96.2%, benefiting from the large Mn···Mn\ndistance. More interestingly, <b>Compound 3</b> showed a highly\nselective response to methanol in a series of tested organic solvents,\nwith a rapid and reversible change in emission color from green to\nred. The single crystal of [Bu(MIm)<sub>2</sub>][MnBr<sub>4</sub>]·CH<sub>3</sub>OH with red emission proved that the luminescence switching\nwas attributed to the adsorption of CH<sub>3</sub>OH molecules into\nthe lattice space in the form of the O–H···Br\nhydrogen bonds. To our knowledge, for tetrahedrally coordinated Mn(II)\nspecies, the reversible emission color switching between green and\nred triggered by a solvent without the change of coordination number\nis achieved for the first time, providing promising applications for\nthe specific detection of methanol.