Multi-stimuli Responsive Properties Research Articles

High-contrast tricolor-tunable solid luminescent AIE-active Au(I) isocyanide complexes based on thermo- and mechanochromism

Breaking through the limitations of traditional luminescent materials, integrating the charming aggregation-induced emission (AIE) characteristics, high-contrast mechanochromism and thermochromism into one molecule is of great significance to make stimuli-responsive materials more intelligent. Herein, two Au(I) isocyanide complexes with short alkoxyl chains (C2 and C3) in the solid state are designed and synthesized, the length of the alkoxyl chain exerts significant impacts on molecular arrangement. Both C2 and C3 exhibit obvious AIE properties, the green luminescent aggregate of C2 and C3 is result from J-aggregation while the orange luminescent aggregate of C3 is result from the formation of aurophilic bonds, which supported by the single crystal X-ray analysis. Moreover, C2 and C3 not only display red-shifted mechanochromism (20 nm and 26 nm), but also exhibit gradual blue-shifted thermochromism. A tricolored luminescent switch application was demonstrated using C3 as a multi-stimuli responsive material. This molecular design strategy provides a new avenue for efficient luminescent materials with AIE and multi-stimuli responsive properties.

Multi-stimuli fluorescence responsiveness of α-cyanostilbene derivative: AIEE, stimuli response to polarity, acid, force and light, applications in anti-counterfeiting and single phosphor w-OLED

Recently, the small molecule functional materials with a simple synthesis have attracted more and more attention. A multi-stimuli-responsive aggregation-induced emission (AIE) molecule is expected to have great applications in the near future. Identically, the single-component white organic light diode (w-OLED) has a good application field. Herein, a cyanostilbene derivative (TSC) was efficiently synthesized by Vilsmeier and Knoevenagel reactions with only 2 steps under mild conditions. TSC was characterized by NMR (1H, 13C), FT-IR, HRMS and elemental analysis. TSC has aggregation-induced enhanced emission (AIEE) effect, and significant polar-, acid-, force- and light-stimuli fluorescence responsiveness properties. The AIE effect and four different stimulus responses are all simultaneously presented in TSC. This phenomenon is relatively rare in small molecule fluorescent compounds. The results of SEM and DLS reveal the AIEE of TSC is mainly due to the fact that molecular self-assembly into nanofiber networks in the aggregated state limiting the distortion of molecules. DFT calculations show that the polarity stimuli-response (fluorescence from green to orange) is closely related to intramolecular charge transfer (ICT). Acid/base 1H NMR titration proves that the acidochromism results from reversible protonation/deprotonation. The results of DSC, SEM, PXRD and POM prove that the essence of mechanical force stimuli-response is the change of crystallinity. The results of 1H NMR, UV–vis and fluorescence spectra, DFT calculations and SEM reveal that the light stimuli-response is attributed to the Z/E configuration transformation. Based on multi-stimuli responsive properties, TSC can be used for recognition of solvents polarity by naked eyes or fluorophotometer, used as an acid indicator and also used to quantitatively test the concentration of trace acids, used in anti-counterfeiting including safty ink, data rewriting, even can be used to construct supramolecular liquid crystals materials. In addition, TSC can be used to fabricate single phosphor w-OLED, avoiding using multicomponent composite materials.

Colorful variation of tetraphenylethene derivatives in the solid state

This review provides a clear overview of the multi-stimuli responsive properties of tetraphenylethene derivatives in the solid state.

Structural tuning of β-enamino diketones: exploration of solution and crystalline state photochromism.

A library of β-enamino diketones was prepared via base-mediated, three-component reaction of 4-hydroxycoumarins with various aromatic/aliphatic amines and β-nitrostyrenes under microwave irradiation conditions to investigate their photochemical properties. Among the prepared compounds, a thiophene derived β-enamino diketone was found to be light-sensitive and to exhibit unique photochromic behavior, that is, positive photochromism in solution and negative photochromism in crystalline phase. In addition, this prepared photochromic compound was further covalently linked to a structure-related, piezochromic β-enamino diketone moiety to explore its potential multi-stimuli responsive properties.

Cyanostyrene derivative with multi-stimuli responsive properties: Multicolor- and high-color-contrast switching in response to force, heat and light

Multi-stimuli responsive luminescent materials are ideal materials for luminescent anti-counterfeiting technology. Currently, it is still challenging to develop excellent multi-stimuli-responsive material that is easy to synthesize and low-cost. Herein, a dicyanostilbenebenzene derivative (α-CFP) with a symmetrical structure was designed and successfully synthesized, which showed obvious AIE and solvent effects in solution. Two polymorphs of it were prepared by controlling the cooling rate, and it was found that green-emitting Form I and blue-emitting Form II can transform into each other by heat and mechanical force. Crystal structure analysis reveals the possible intrinsic mechanism of polymorphism-dependent emission and interconversion. Further studies found that both Form I and Form II could transform into another new polymorph Form III upon heating to 220 °C. Form III can undergo photoinduced [2 + 2] cycloaddition reaction accompanied by discoloration, and it can return to its original state by heating. Finally, three application scenarios were designed and demonstrated, which confirm their potential applications in information encryption and anti-counterfeiting.

Dehydroabietic acid and triphenylamine combined BioAIEgens with an imine linker and RIM: mechanochromism and acidichromism

The petrochemical-based multi-stimuli responsive materials have been widely explored as advanced functional materials in the past several decades, but they inevitably face problems like complicated synthesis, non-renewability, and non-sustainability. On this basis, the bio-based materials used to construct multi-stimuli responsive due to the unique natural structures have come to the fore. In this work, three novel triphenylamine-based salicylideneanilines have been simply designed with aggregation-induced emission (AIE) properties. Among all, DAMB-TPAOH and DAMB-TPA possessing the natural structure of dehydroabietic acid from rosin are bioproduct-inspired AIE luminogens (BioAIEgens). Derived from the excited-state intramolecular proton transfer (ESIPT) and restriction of intramolecular motion (RIM) dual-mechanism caused by the hydroxyl group and rigidification of alicyclic moiety, respectively, the solid-state DAMB-TPAOH exhibits red-shifted (compared to DAMB-TPA) and stronger (compared to BA-TPAOH) emission, endowing this BioAIEgen with the best fluorescence behavior. Further, the introduction of the natural skeleton, propeller TPA, and imine group results in the high-contrast mechanochromic and acidichromic properties of DAMB-TPAOH. The multi-stimuli responsive properties endow DAMB-TPAOH with potential utilization in the manufacture of rewritable paper and multi-color ink. The current work contributes greatly to the development of BioAIEgens with both mechanochromism and acidichromism.

A novel multi-stimuli responsive fluorescence liquid crystal material with aggregation-induced emission effect

ABSTRACT Scientists are faced with a formidable problem in improving the smart properties of multi-stimuli responsive fluorescent materials. Here, we integrated two kinds of stimuli-responsive materials: aggregation-induced emission (AIE) and liquid crystals (LCs) into one system. An AIE-active fluorescence liquid crystal compound of α-cyanodistyrene derivate Py-CN-LBM8 was synthesised using knoevenagel condensation reaction. Its AIE effect, LC behaviour, multi-stimuli responsive properties and mechanisms were investigated by polarised optical microscopes (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), UV-visible (UV-vis) absorption spectra and photoluminescence (PL) spectra. The results showed that Py-CN-LBM8 exhibited significant physical response to external stimuli including temperature, mechanical force, solvent, pH and trace water. This work provided a strategy for designing new multi-stimuli responsive materials and made it possible to apply in the multifunction anti-counterfeit, sensor and information storage fields.

Solvent-induced MultiStimuli-Responsive properties of cyano-substituted Oligo(p-phenylene vinylene) derivatives

Stimuli-responsive luminescent materials with controllable photophysical properties have attracted much attention because of their potential applications in smart materials and devices. Through the incorporation of electron-donating (NPh3) and electron-withdrawing (CN) functionalities, two donor-acceptor luminophores C4OPV-TPA and C8OPV-TPA bearing two different alkyl chain lengths were prepared and fully characterized. Although both C4OPV-TPA and C8OPV-TPA exhibited similar luminescence and AIEE effects in solution with intramolecular charge-transfer (ICT) transition, remarkable differences were observed in the self-assemble state. Specifically, precipitation of C4OPV-TPA into toluene and CH2Cl2, respectively, afforded two distinctly crystallines, with one in orange color (O-state) and the other in red color (R-state). Notably, C4OPV-TPA in O-state exhibited stimuli-responsive behaviors in solid state, which were ascribed to the formation of an inclusion complex with toluene molecules. Under thermal heating and mechanical grinding, toluene was released from crystal lattice of luminophore accompanied with red-shifted emission spectra. The molecular packing of C4OPV-TPA in R-state, on the other hand, adopted stronger H-aggregates without inclusion of CH2Cl2 molecules, which was further investigated by X-ray diffraction. These excellent optical properties enabled C4OPV-TPA serve as a fluorescent ink for thermal-responsive data storage device.

White-light-emitting Ln-hydrogels with multi-stimuli responsiveness and applications in environmental sensing and anti-counterfeiting.

The construction of smart materials, especially white light emitting (WLE) hydrogels with multi-stimuli responsive properties, has received widespread attention from researchers. In this study, a WLE hydrogel was obtained by the in situ doping of Eu3+ and Tb3+ into a blue emission low molecular weight gelator (MPF). Remarkably, the prepared WLE hydrogel possessed excellent stimuli responsiveness to pH, temperature and chemicals, and could be used as a soft thermometer and a selective sensor for Cu2+. The correlated color temperature of the WLE hydrogel was calculated to be 5063 K, suggesting a potential application in cool white light. Moreover, a series of metallohydrogels with different colors were obtained by modulating the ratio of MPF, Eu3+ and Tb3+ or changing the excitation wavelength, which was an excellent candidate to construct soft materials of a full-color system. Additionally, the WLE hydrogel could be used for constructing anti-counterfeiting materials. Therefore, this study provides a new approach for preparing smart WLE hydrogels with multiple functions.

α-Cyanostilbene functionalized carbazole derivatives exhibiting dual-state emission and multi-stimuli responsive fluorescent switching

Interest in organic luminescent materials that show strong dual state emission (DSE) in both solution and the solid state is rapidly growing due to their widespread applications. The development of DSE luminogens (DSEgens) with multi-stimuli responsive properties capable of achieving multi-parameter detection in complicated environments remains challenging due to the lack of an explicit molecular design strategy. In this work, we devised and prepared two D-π-A-π-D-structured carbazole derivatives, PY-CZ-Pa and PY-CZ-Ta, with intramolecular charge transfer (ICT) characteristics and excellent DSE properties. Both the compounds as fluorescent probes are highly sensitive to trace amount of water and picric acid (PA) in organic solvents. The limits of detection are determined to be 0.016% (PY-CZ-Pa) or 0.040% (PY-CZ-Ta) for water and 320 nM (PY-CZ-Pa) or 538 nM (PY-CZ-Ta) for PA. Moreover, the two compounds exhibit reversible mechanofluorochromism, with spectral shifts of over 24 nm. The results presented in this work suggest that bright DSEgens with multi-stimuli responsive properties are promising materials for applications at both the molecular and aggregated levels.

A multi-responsive system based on intramolecular B ← OP Lewis acid–base pairs

Novel intramolecular B ← OP compounds were synthesized, which can exhibit multi-stimuli responsive properties upon tuning the dynamic B–O bond strength.

D–A–D structured triphenylamine fluorophore with bright dual-state emission for reversible mechanofluorochromism and trace water detection

A donor–acceptor–donor-structured triphenylamine chromophore showing bright dual-state emission (DSE) has been synthesized and demonstrated multi-stimuli responsive properties, including water response, mechanochromism, and solvatochromism.

Spiropyran-incorporated honeycomb porous films with reversible multistimuli-responsive properties

Spiropyran-modified honeycomb porous film with photo-, thermo- and acido-chromic properties.

Mechanical Bending and Modulation of Photoactuation Properties in a One-Dimensional Pb(II) Coordination Polymer

With emergent research on stimuli responsive materials, dynamic crystals are at the forefront of investigation. However, research on the mechanical properties of coordination polymers (CPs) is still in its infancy. Elastic deformation induced by pressure and photoactuation are rare occurrences in CPs, let alone their combination in a single CP. Here, we report a one-dimensional (1D) CP comprising PbBr2 chains with 3-fluoro-4’-styrylpyridine arms showing excellent elasticity and photomechanical properties. A slender crystal can be bent to make a circle and write different shapes with restoration of original shape upon removal of the applied force. In addition, photomechanical properties triggered by [2+2] cycloaddition of the olefinic ligand can be modulated easily by variation of the crystal sizes. Crystals with bigger width show destructive photosalient effects while the smaller ones show plastic deformation like bending, twisting, curling etc. upon UV irradiation. This example provides avenue for designing CPs for multi-stimuli responsive actuating properties.

A multi-stimuli responsive tetraphenylethene derivative: Self-reversible mechanochromism, mechanoluminescence, switchable photochromism

Most of the reported stimuli-responsive aggregation induced emission (AIE) molecules are single-functioned and it remains highly demanded to integrate multi-stimuli responsive properties in one molecule. A multi-stimuli responsive TPE derivative 1 was synthesized bearing multiple properties including mechanochromism, mechanoluminescence and photochromism. Mechanoluminescence was only shown by the single crystal form, while photochromism was only observed in the amorphous powder. The mechanochromic property of 1 was self-reversible, but can also be accelerated by thermal or solvent vapor treatment. The photochromic property of 1 was easily switched on by a phase transition from crystalline state to amorphous state upon grinding. By a combination of mechanochromism and photochromism, a two-step procedure of color response of 1 was demonstrated upon grinding and UV irradiation. This novel molecule provides an important insight to the development of multi-stimuli responsive materials and advanced anti-counterfeiting materials.

Multi-stimuli responsive properties and structure–property studies of tetraphenylethylene functionalized arylimidazole derivatives

Tetraphenylethylene functionalized arylimidazole derivatives G4, G3, G2, L-G4, L-G3 and L-G2 with multi-stimuli responsive properties have been designed and synthesized.

AIE-based donor–acceptor–donor fluorenone compound as multi-functional luminescence materials

A novel fluorenone-based luminescent material with multi-stimuli responsive and multi-functional properties is reported.

Multi-Stimuli Responsive Luminescent β-Diketones and Difluoroboron Complexes with Heterocyclic Substituents.

Emissive β-diketones (bdks) and difluoroboron complexes (BF2bdks) exhibit multi-stimuli responsive luminescence, including solvatochromism, viscochromism, aggregation induced emission, thermal and mechanochromic luminescence, halochromism and pH sensing. In this study, a series of six-membered heterocycle-substituted (piperidine, morpholine, 1-methyl piperazine) bdk ligands and boron complexes were synthesized, and their luminescent properties were investigated. All the compounds exhibited red-shifted emission in more polar solvents due to intramolecular charge transfer as well as higher emission intensity in more viscous environments. In response to solubility changes in water/tetrahydrofuran mixtures, while the piperazine bdk ligand showed aggregation caused quenching, the piperidine and morpholine bdks displayed enhanced emission upon aggregation. In the solid state, all ligands exhibited mechanochromism. More dramatic halochromism was observed for the piperidine boron dye spin cast film. In solution, for the boron dyes under varying pH values (1-13), different protonated and deprotonated forms were analyzed according to the measured emission spectra. Graphical abstract Multi-stimuli responsive luminescent properties were investigated for the six-membered heterocycle-substituted β-diketone ligands and difluoroboron complexes.

White-Light-Emitting AIE/Eu3+-Doped Ion Gel with Multistimuli-Responsive Properties.

A white-light-emitting ion gel composed of a poly[(2-(4-vinylphenyl)ethene-1,1,2-triyl)tribenzene-b-ethylene glycol-b-(2-(4-vinylphenyl)ethene-1,1,2-triyl)tribenzene] aggregation-induced emission (AIE) network and a poly([2,2':6',2″-terpyridin]-4'-yl methacrylate-co-methyl methacrylate) Eu3+-doped network was fabricated via a solution mixing process. This ion gel exhibits special multistimuli-responsive properties, and it can change its luminescent color by changing pH, temperature, or the solvent. The unique color-changing property is attributed to the different luminescent mechanisms of the AIE/Eu3+-doped polymer networks. The former is affected by changes in its aggregation state, while the latter is controlled by the dynamic metal-ligand cross-linking bonds. Furthermore, owing to the interpenetrating networks formed by the two polymers, the hybrid gel has both good mechanical strength and flexibility. It may be used in the fields of sensors, probes, and light-emitting materials.

Combining Theory and Experiment to Get Insight into the Amorphous Phase of Luminescent Mechanochromic Copper Iodide Clusters.

In the field of stimuli-responsive luminescent materials, mechanochromic compounds exhibiting reversible emission color changes activated by mechanical stimulation present appealing perspectives in sensor applications. The mechanochromic luminescence properties of the molecular cubane copper iodide cluster [Cu4I4[PPh2(C6H4-CH2OH)]4] (1) are reported in this study. This compound can form upon melting an amorphous phase, giving an unprecedented opportunity to investigate the mechanochromism phenomenon. Because the mechanically induced crystalline-to-amorphous transition is only partial, the completely amorphous phase represents the ultimate state of the mechanically altered phase. Furthermore, the studied compound could form two different crystalline polymorphs, namely, [Cu4I4[PPh2(C6H4-CH2OH)]4]·C2H3N (1·CH3CN) and [Cu4I4[PPh2(C6H4-CH2OH)]4]·3C4H8O (1·THF), allowing the establishment of straightforward structure-property relationships. Photophysical and structural characterizations of 1 in different states were performed, and the experimental data were supported by theoretical investigations. Solid-state NMR analysis permitted quantification of the amorphous part in the mechanically altered phase. IR and Raman analysis enabled identification of the spectroscopic signatures of each state. Density functional theory calculations led to assignment of both the NMR characteristics and the vibrational bands. Rationalization of the photoluminescence properties was also conducted, with simulation of the phosphorescence spectra allowing an accurate interpretation of the thermochromic luminescence properties of this family of compounds. The combined study of crystalline polymorphism and the amorphous state allowed us to get deeper into the mechanochromism mechanism that implies changes of the [Cu4I4] cluster core geometry. Through the combination of multistimuli-responsive properties, copper iodide clusters constitute an appealing class of compounds toward original functional materials.