Legislative Documents

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Tuning Light-Driven Motion and Bending in Macroscale-Flexible Molecular Crystals Based on a Cocrystal Approach

Flexible molecular crystals with stimuli-responsive properties are highly desirable; however, uncovering them is still a challenging goal. Herein, we report a cocrystal approach to obtain elastic molecular crystals that exhibit light-induced fluorescence changes and dynamic mechanical responses at the macroscale level. Cocrystals of naphthylvinylpyridine and tetrafluoroterephthalic acid were fabricated in different stoichiometry ratios (2:1 and 1:1), which present different shapes [two-dimensional (2D) and one-dimensional (1D) morphologies], photoemission, and mechanical properties (rigidity and flexibility). Moreover, obviously different photomechanical energy conversions (light-driven cracking/popping and bending/motion) occur for the 2D and 1D cocrystals, respectively. Nuclear magnetic resonance (NMR) spectra show the occurrence of photoinduced [2 + 2] cycloaddition in both cocrystals, which is the primary mechanism for their photoactuating behaviors. Crystal structure analysis and theoretical calculation further reveal that protonation and the hydrogen-bonding network play important roles in light-stimulus-bendable 1D cocrystal. Thus, the transformation from rigidity to flexibility based on cocrystallization with different stoichiometry may offer an effective means to tune the dynamic light-driven responses for smart crystalline materials

Tuning Light-Driven Motion and Bending in Macroscale-Flexible Molecular Crystals Based on a Cocrystal Approach

Flexible molecular crystals with stimuli-responsive properties are highly desirable; however, uncovering them is still a challenging goal. Herein, we report a cocrystal approach to obtain elastic molecular crystals that exhibit light-induced fluorescence changes and dynamic mechanical responses at the macroscale level. Cocrystals of naphthylvinylpyridine and tetrafluoroterephthalic acid were fabricated in different stoichiometry ratios (2:1 and 1:1), which present different shapes [two-dimensional (2D) and one-dimensional (1D) morphologies], photoemission, and mechanical properties (rigidity and flexibility). Moreover, obviously different photomechanical energy conversions (light-driven cracking/popping and bending/motion) occur for the 2D and 1D cocrystals, respectively. Nuclear magnetic resonance (NMR) spectra show the occurrence of photoinduced [2 + 2] cycloaddition in both cocrystals, which is the primary mechanism for their photoactuating behaviors. Crystal structure analysis and theoretical calculation further reveal that protonation and the hydrogen-bonding network play important roles in light-stimulus-bendable 1D cocrystal. Thus, the transformation from rigidity to flexibility based on cocrystallization with different stoichiometry may offer an effective means to tune the dynamic light-driven responses for smart crystalline materials

Ultralong Persistent Room Temperature Phosphorescence of Metal Coordination Polymers Exhibiting Reversible pH-Responsive Emission

Ultra-long-persistent room temperature phosphorescence (RTP) materials have attracted much attention and present various applications in illumination, displays, and the bioimaging field; however, the persistent RTP is generally from the inorganic phosphor materials to date. Herein, we show that the metal coordination polymers (CPs) could be new types of emerging long-lived RTP materials for potential sensor applications. First, two kinds of Cd-based CPs, Cd­(<i>m</i>-BDC)­(H₂O) (<b>1</b>) and Cd­(<i>m</i>-BDC)­(BIM) (<b>2</b>) (<i>m</i>-BDC = 1,3-benzenedicarboxylic acid; BIM = benzimidazole), were obtained through a hydrothermal process, and the samples were found to exhibit two-dimensional layered structures, which are stabilized by interlayer C–H···π interaction and π···π interaction, respectively. The CPs show unexpected second-time-scale ultra-long-persistent RTP after the removal of UV excitation, and this persistent emission can be detected easily on a time scale of 0–10 s. The CPs also feature a tunable luminescence decay lifetime by adjusting their coordination situation and packing fashion of ligands. Theoretical calculation further indicates that the introduction of the second ligand could highly influence the electronic structure and intermolecular electron transfer toward tailoring the RTP of the CP materials. Moreover, CP <b>2</b> exhibits well-defined pH- and temperature-dependent phosphorescence responses. Therefore, this work provides a facile way to develop new type of CPs with steady-state and dynamic tuning of the RTP properties from both experimental and theoretical perspectives, which have potential applications in the areas of displays, pH/temperature sensors, and phosphorescence logic gates. On account of suitable incorporation of inorganic and organic building blocks, it can be expected that the ultra-long-persistent RTP CPs can be extended to other similar systems due to the highly tunable structures and facile synthesis routes

Flexible Self-Supporting Nanofibers Thin Films Showing Reversible Photochromic Fluorescence

Highly sensitive stimuli-responsive fluorescent films play an important role in smart sensors and readable optical devices. However, systems involving light-driven fluorescence changes are still limited compared with photochromic materials that simply change color upon photostimulation. Herein, by incorporation of stilbene-based molecules into a poly­(vinyl alcohol) host, we have developed new flexible self-supporting nanofiber films that exhibited fast and obvious photochromic fluorescence (PCF). The reversible transfer between two fluorescent states can be easily recycled. Fluorescence microscopy and atomic force microscopy images supplied in situ evidence of changes in fluorescence and surface morphology, respectively. Density functional theoretical calculations showed that the PCF can be attributed to photoisomerization of the stilbene-based molecules. Therefore, based on the combination of experimental and theoretical studies, this work not only supplies new stilbene-based systems with light-induced fluorescence change, but also gives detailed understanding on the photoisomerization and PCF processes of the nanofibers systems. We anticipate that these PCF films can be applied in erasable memory devices and antiforgery materials, and that our strategy may be extended to other systems to fabricate multistimuli-responsive fluorescent materials

Fast and Reversible Humidity-Responsive Luminescent Thin Films

Highly sensitive stimuli-responsive fluorescent films are playing an increasingly important role in the development of smart sensors and erasable optical devices. However, systems involving humidity-responsive fluorescence (HRF) are still very limited compared to those responsive to other common environmental stimuli (e.g., light, heat, pressure, or pH). Herein, by incorporating the 4-[4-(dimethylamino)­styryl]­pyridine chromophore into a polyvinylpyrrolidone host, we have developed new flexible self-supporting nanofiber films that exhibit fast and obvious HRF. The reversible transformation between two fluorescence states can be easily observed and recycled at least 200 times. Fluorescence microscopy images provided in situ evidence of changes in both fluorescence and morphology. This work therefore offers an alternative to conventional humidity sensors based on changes in color and electrical properties. Furthermore, we anticipate that these HRF films can also be employed as optical antiforgery materials

Niflumic Anion Intercalated Layered Double Hydroxides with Mechano-Induced and Solvent-Responsive Luminescence

Stimuli-responsive luminescent materials play an important role in fluorescent switches, optical storage devices and smart sensors. In this work, we report a mechano-induced and solvent stimuli-responsive luminescent change by the assembly of a typical aggregation-induced-emissive (AIE) molecule, niflumic acid (NFC), into the interlayer region of Zn–Al-layered double hydroxides (LDHs) with heptanesulfonate (HPS) as a cointercalation guest. The structure, chemical composition, and thermostability of the as-prepared NFC-HPS/LDHs composites were characterized by X-ray diffraction, elemental analysis, and thermogravimetry and differential thermal analysis (TG-DTA). Fluorescence spectra demonstrate that the sample with 5% NFC initial molar percentage, with respect to the interlayer guests, exhibits the optimal luminescent intensity. The NFC-HPS/LDH (5%) sample also exhibits the most obvious luminescent mechano-response with a 16 nm blue-shift and increase in the fluorescent intensity after grinding, while the pristine NFC solid shows little to no mechano-responsive behavior. Moreover, the NFC-HPS/LDH (5%) also presents reversible luminescent response to different volatile organic compounds (VOCs) (such as tetrahydrofuran, methanol, acetone, toluene, and chloroform). Therefore, this work not only gives a detailed description on the dual stimuli (mechanics and solvent)-responsive luminescence for future sensor applications but also supplies a deep understanding of the optical properties of the new AIE molecule within the confined LDH layers

Layered Dinitrostilbene-Based Molecular Solids with Tunable Micro/Nanostructures and the Reversible Fluorescent Response to Explosives

The ability to modulate and control the fluorescence properties of molecular solids at the micro/nanoscale is important to develop high-performance optoelectronic materials and sensors. Here we report the tunable one-photon and two-photon fluorescence as well as micro/nanostructures of dinitrostilbene-based (DNS) chromophore by the formation of layered multicomponent crystals with guanidinium cation (GD) through hydrogen-bonding assembly. The as-prepared GD₂DNS bulk crystal shows a red-shift emission as well as enhanced photoluminescence quantum yield and fluorescence lifetime compared with those of the Na₂DNS sample, which is related to the structural transfer of DNS from staggered arrangement to parallel fashion within the crystal. Periodic density functional theoretical calculations further show that the introduction of different cationic units can modify the frontier orbital distribution and electronic structure of DNS anions within the multicomponent crystals. Moreover, one-dimensional GD₂DNS nanobelts with well-aligned orientation can be further obtained by a combined ultrasound and coprecipitation method. The GD₂DNS nanobelts undergo a blue-shift fluorescence compared with its bulk crystal, and exhibit alternated photoresponse (such as emission wavelength and intensity) upon interaction with different nitroaromatic explosives (trinitrotoluene, picric acid and m-dinitrobenzen). Therefore, this work gives a facile bottom-up self-assembly rout to prepare organic multicomponent materials with tunable fluorescence properties and micro/nanostructures, which can be potentially used as luminescence detector for nitroaromatic explosives