Linear Regulation of Red Emission in an Organic–Inorganic Manganese Bromide via Pressure

Organic–inorganic
metal halides (OIMHs) can show
diverse
optical properties under pressure since their emission pathways can
be facilely manipulated through hydrostatic compression. However,
pressure-induced phase transitions and their irreversibility disrupt
the linear tuning of the pressure-dependent optical properties, thereby
hampering their applications in pressure sensing. To improve structural
stability, we introduced O–H···Br interactions
and synthesized a zero-dimensional (0D) manganese-based (Mn-based)
OIMH, (TDMA)MnBr3(H2O)2 [TDMA = (tetrahydrofuran-3-yl)methylammonium],
with a 625 nm phosphorescence emission. For pressure-induced discoloration,
high pressure enhances the crystal field splitting energy of Mn2+ through octahedral compression and distortion, which leads
to the decrease of the band gap and the red shift of the emission
wavelength. Above all, the strong O–H···Br interactions
formed between adjacent octahedra have effectively improved the structural
stability and suppressed phase transitions under high pressure, which
promotes the generation of a highly linear pressure–emission
wavelength correlation. This encouraging result opens up the potential
applications of pressure sensing within the red emission of 0D Mn-based
OIMHs.

有机-无机金属卤化物（organic–inorganic metal halides，OIMHs）可在高压环境下展现出多样的光学特性，其发光路径可通过静水压压缩实现便捷调控。然而，压力诱导的相变及其不可逆性会破坏光学特性随压力的线性调控规律，进而阻碍其在压力传感领域的应用。为提升结构稳定性，我们引入了O–H···Br相互作用，合成了一种零维（zero-dimensional，0D）锰基（manganese-based，Mn基）OIMH：(TDMA)MnBr₃(H₂O)₂ [TDMA = 四氢呋喃-3-基甲基铵（tetrahydrofuran-3-ylmethylammonium）]，其磷光发射波长为625 nm。针对压力诱导的变色现象，高压通过八面体压缩与畸变提升了Mn²+的晶体场分裂能（crystal field splitting energy），进而导致带隙（band gap）减小、发射波长红移。尤为关键的是，相邻八面体之间形成的强O–H···Br相互作用，有效提升了高压下的结构稳定性并抑制了相变，从而促成了压力与发射波长之间的高度线性相关关系。这一令人振奋的成果为零维锰基OIMHs的红光发射在压力传感领域的潜在应用开辟了道路。