Highly emissive coordination polymer derived from tetraphenylethylene-tetrazole chromophore:Synthesis,characterization and piezochromic luminescent behavior

Solid-state materials that exhibit pressure stimulus-response characteristics in a manner of emission signal,known as piezochromic luminescence(PCL),demonstrate great potential in photoelectric devices.The weakened luminescence and insignificant color change in the aggregation state,however,hampers their practical applications.Herein,a highly emissive coordination polymer,[Zn2(H4TTPE)(H2O)4]·H2O(CUST-805),is successfully constructed by employing an AIE-active chromophore as the building block.The structural characterization and photophysical properties are systematically studied.Owing to intrinsic twisted conformation and AIE feature of tetraphenylethylene-tetrazole ligand,CUST-805 achieves the visible and reversible PCL from blue to green switched by different external stimuli.The transformation between crystalline and amorphous states is proved to be the origin of present PCL behavior.Moreover,on basis of electron and energy transfer quenching mechanism,the highly selective and sensitive sensor based on CUST-805 is realized,showing the low detection limit of 0.29 ppm towards 2,4,6-trinitrophenol.

Thiomethyl Derivatives of Two Oligo(p-phenylene vinylenes) as New Aggregation-Induced Piezofluorochromic Emitters

Two piezochromic fluorescent compounds are prepared by introducing thiomethyl substituents to the peripheralpositions of two related cyano oligo(p-phenylene vinylenes) (CN-OPV). The new derivatives, namely, 1,4-bis[2-cyano-2(4-thiomethylphenyl)ethenyl]benzene (TOPV1) and 1,4-bis(1-cyano-2-(4-thiomethylphenyl)ethenyl) benzene (TOPV2), are characterized by NMR, powder X-ray diffraction data (XRD) and differential scanning calorimetric (DSC) data. UV-Vis and fluorescence spectra are also measured. TOPV1 with the cyano groups farther away from the central aromatic ring is photoluminescent, and on application of pressure exhibits a more obvious color change and higher Stokes shift than those measured for TOPV2. We also observe piezochromic aggregation-induced emission (PAIE) for TOPV2, but TOPV1 does not exhibit any PAIE.

Pressure effects on metal/covalent-organic frameworks:structural and optical properties

Metal-organic frameworks(MOFs)and covalent organic frameworks(COFs)with highly ordered porous structure,tunable bandgap,large specific surface area and structural diversity,provide an appealing platform for the development of stimulus response,sensing,imaging and optoelectronics.Among various tuning methods,pressure engineering using the diamond anvil cell is a highly powerful in-situ technique,which can efficiently modulate the structural and optical properties of MOFs/COFs.This is beyond the realization of traditional chemical methods.This review outlines the research progress in the experimentoriented discovery of new phases or unique properties under high pressure,including phase transition,abnormal compression,photoluminescence(PL)discoloration and enhancement.Notably,the improvement of PL quantum yield in MOFs could be achieved by pressure-treated engineering and hydrogen-bonding cooperativity effect.We also propose and establish the relationship between structure and optical properties under high pressure.Finally,the challenge and outlook of the current fields are summarized.We hope that this review will supply guidance for comprehending the development of high-pressure MOF/COF-related research fields,and offer novel strategies for designing more high-performance MOF/COF materials to ultimately expand their applications.

Recent advances in organic pressure-responsive luminescent materials

Organic luminescent materials are very sensitive to external stimuli,such as pressure,temperature,and electric field.The luminescent properties of some organic luminescent materials significantly change under high pressure.Some materials may show luminescence discoloration,whereas some may exhibit luminescence enhancement.These properties have many potential applications in anticounterfeiting,force sensor,data recording and storage,and luminescent devices,thereby greatly attracting the attention of scientists.In this review,the progress of research on these materials at high pressure in recent years is summarized.

Pressure-induced photoluminescence enhancement and ambient retention in confined carbon dots

Piezochromic luminescent materials have shown great potential in advanced optoelectronic applications.However,most of luminescent materials usually undergo emission quenching under external stimuli.Herein,we demonstrate for the first time that the photoluminescence of carbon dots(CDs)confined within sodium hydroxide can be enhanced when high pressure is applied.They exhibit a 1.6-fold fluorescence enhancement compared with pristine CDs.Importantly,the enhanced fluorescence intensity can be retained after the release of pressure to ambient conditions.A combination of experimental analysis and theoretical simulations indicates that such an enhanced emission is mainly attributed to the strong confinement resulting from the sodium hydroxide matrix,which can separate the CDs spatially and restrict the nonradiative pathway.These results provide a rational strategy for manipulating the optical properties of CDs with enhanced and retainable photoluminescence(PL)performance,thus opening up a venue for designing luminescent CDs-based materials.

Manipulating Emission Enhancement and Piezochromism in Two-Dimensional Organic–Inorganic Halide Perovskite[(HO)(CH_(2))_(2)NH_(3)]_(2)PbI_(4)by High Pressure

Two-dimensional(2D)organic–inorganic halide perovskites present remarkable stability and diversity and are promising alternatives to their three-dimensional(3D)counterparts.The 2D halide perovskite[(HO)(CH_(2))_(2)NH_(3)]_(2)PbI_(4)is regarded as a superior moisture-stabile“smooth”perovskite because of distinct hydrogen-bond networks that connect adjacent organic–inorganic layers.