Synthesis And Luminescence Properties Of Metal Halides With Complex/organic Cation

Recently,zero-dimensional organic-inorganic hybrid metal halides（0D HMHs）have attracted great interest owing to their exceptional structural tunability and intriguing emission properties.They typically exhibit broad emissions with large Stokes shift and high photoluminescence quantum yields due to the strong quantum confinement,soft lattice,and strong electron-phonon coupling.These features endow them with wide applications in liquid crystal displays backlighting,illumination,and scintillators.Progresses in recent years have unraveled the important role of the organic cation in determining the optoelectronic and physicochemical properties of high-dimensional HMHs.In 0D HMHs,metal halide polyhedra have weak interactions with limit organic cations.Therefore,their luminescent properties have seldomly been affected by organic cations.Besides,the soft skeletons of organic cations make it difficult to investage the relationships of HMHs’structure and properties.On the other hand,the enhancement of luminescent properties for HMHs is limited by the weak interactions between organic cations and metal halide polyhedra.The research contents are summarized as follows:Luminescence regulation of Sn-based HMHs:Two kinds of organic cations based on DABCO were co-crystallized with Sn X₂（X=Br,I）to obtain 0D HMHs:(C₈N₂H₁₈)₂Sn X₆ and(C₇N₂H₁₆)₂Sn X₆（X=Br,I）.These two types of hybrid tin bromides share similar structural features with different hydrogen bonding interactions between[Sn Br₆]^4-anions and organic cations.Detailed structural analyses and Hirshfeld surface calculations confirm that the enhanced hydrogen bonding interactions are essential to obtain the multiple emissions in(C₇N₂H₁₆)₂Sn Br₆.Construction of Mn-based HMHs with high photoluminescence thermal stability:a rigid complex cation was constructed by 18-crown-6 with strong chelating effect and Pb²⁺,and then co-crystallized with Mn X₂（X=Cl,Br）to obtain a 0D Mn-based HMHs[Pb(C₁₂O₆H₂₄)X]₂[Mn₂X₆]（X=Cl,Br）.Among them,[Pb(C₁₂O₆H₂₄)Cl]₂[Mn₂Cl₆]exhibits a broad yellow emission under the excitation of blue light（445 nm）,and its photoluminescence quantum yield is near-unity.It was found that the Pb²⁺in the pushpin complex cation[Pb(C₁₂O₆H₂₄)Cl]+has an empty coordination site,which plays an important role in promoting the formation and stabilization of the binuclear tetrahedral anion[Mn₂Cl₆]^2-.Meanwhile,the rigidity of the complex cation[Pb(C₁₂O₆H₂₄)Cl]⁺also greatly enhances the structural rigidity of[Pb(C₁₂O₆H₂₄)Cl]₂[Mn₂Cl₆],reduces the non-radiative transitions,and improves the photoluminescence thermal stability.Construction of HMHs with efficient remote thermometry:Based on complex cations[Pb(C₁₂O₆H₂₄)X]⁺（X=Cl,Br）,a series of HMHs with different metal halide polyhedra were synthesized.The metal halide polyhedra include dimeric tetrahedron,square pyramid,octahedron and so on.The photoluminescence of these HMHs can be tuned from cyan（505 nm）to red（720 nm）.More importantly,two kinds of[Pb(C₁₂O₆H₂₄)X]₂[M₂X₆]（X=Cl,Br;M=Zn）based on group 12 metals（Zn and Cd）exhibit broad cyan emissions.The lifetimes of[Pb(C₁₂O₆H₂₄)Br]₂[M₂Br₆]（M=Zn,Cd）show linear relationships with temperature（93-256 K）,which could be used for remote optical thermometry.Compared to other metal halide materials,it is found that the rigidity of complex cations reduces the phonon-assisted nonradiative process and broadens the linear temperature range of Sn-based,Sb-based HMHs.