A 1,3-Indandione-Functionalized Tetraphenylethene: Aggregation-Induced Emission, Solvatochromism, Mechanochromism, and Potential Application as a Multiresponsive Fluorescent Probe

Preparation of Langmuir-Blodgett Films from Quinoxalines Exhibiting Aggregation-Induced Emission and Their Acidochromism

The development of aggregation-induced emission (AIE)-exhibiting compounds heavily relies on our evolving comprehension of their behavior at interfaces, an understanding that still remains notably limited. In this study, we explored the preparation of two-dimensional (2D) sensing films from 2,3-diphenylquinoxaline-based diazapolyoxa- and polyazamacrocycles displaying AIE via the Langmuir-Blodgett (LB) technique. This systematic investigation highlights the key role of the heteroatom-containing tether of 2,3-diphenylquinoxalines in the successful fabrication of Langmuir layers at the air-water interface and the transfer of AIE-emitting supramolecular aggregates onto solid supports. Using both diazapolyoxa- and polyazamacrocycles, we prepared AIE-exhibiting monolayer films containing emissive supramolecular aggregates on silica, mica, and quartz glass and characterized them using ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopies, atomic force microscopy (AFM) imaging, and fluorescence microscopy. We also obtained multilayer AIE-emitting films through the LB technique, albeit with increased complexity. Remarkably, by employing the smallest macrocycle N2C3Q, we successfully prepared LB films suitable for the visual detection of acidic vapors. This sensing material, which contains a much lesser amount of organic dye compared with traditional drop-cast films, can be regenerated and utilized for real-life sample analysis, such as monitoring the presence of ammonia in the air and the freshness of meat.

C3-Symmetric Luminescent Diketone with Amido-Linkage as a Polymorphic Fluorescence Emitter

The study introduces a novel C3-symmetric β-diketone compound, BTA-D3, and its monomeric counterpart, D, with a focus on their synthetic procedure, photophysical properties and aggregation behavior. Both compounds exhibit characteristic absorption and weak fluorescence in solution, with BTA-D3 displaying higher absorption coefficients due to its larger number of diketone units. Density Functional Theory (DFT) calculations suggest increased co-planarity of diketone groups in BTA-D3. A significant finding is the Aggregation-Induced Emission (AIE) property of BTA-D3, as its fluorescence intensity increases dramatically when exposed to specific solvent ratios. The AIE behavior is attributed to intermolecular excitonic interaction between BTA-D3 molecules in self-organized aggregates. We also studied fluorescence anisotropy of BTA-D3 and D. Despite its larger size, BTA-D3 showed reduced anisotropy values because of efficient intramolecular energy migration among three diketone units. Furthermore, BTA-D3 demonstrates unique polymorphism, yielding different emission colors and structures depending on the solvent used. A unique approach is presented for promoting the growth of self-organized aggregate structures via solvent evaporation, leading to distinct fluorescence properties. This research contributes to the understanding of C3-symmetric structural molecules and provides insights into strategies for controlling molecular alignment to achieve diverse fluorescence coloration in molecular materials.

Near-infrared fluorescent probe with large Stokes shift for specific detection of lysine

A new near-infrared (NIR) fluorescent probe CL based on coumarin- dicyanoisophorone was synthesized. Addition of Lys to probe CL solution in DMF/H2O (9:1, v/v) medium resulted in noticeable enhancement in the intensity of the fluorescence emission at 702 nm, accompanying distinct color change from yellow to pink. While addition of other amino acids and biothiols (Gly, Hcy, GSH, Glu, Val, Tyr, Arg, Trp, Lys, His, Leu, Phe, Asp and Met) did not bring about substantial changes in both fluorescence emission and color. The detection limit was calculated to be 0.51 μM. Job's plot test revealed that probe CL and Lys formed a complex of 1:1 stoichiometry. Probe CL showed high stability and could be used to recognize Lys in a wide pH range of 4.0-10.0. The sensing mechanism was proposed and verified by 1H NMR spectral measurement. The dual-modal fluorescence turn-on and colorimetric NIR probe with an extremely large Stokes shift of 280 nm may be utilized for highly specific and practical sensing of Lys.

Stimuli-fluorochromic smart organic materials

Smart materials based on stimuli-fluorochromic π-conjugated solids (SFCSs) have aroused significant interest due to their versatile and exciting properties, leading to advanced applications. In this review, we highlight the recent developments in SFCS-based smart materials, expanding beyond organometallic compounds and light-responsive organic luminescent materials, with a discussion on the design strategies, exciting properties and stimuli-fluorochromic mechanisms along with their potential applications in the exciting fields of encryption, sensors, data storage, display, green printing, etc. The review comprehensively covers single-component and multi-component SFCSs as well as their stimuli-fluorochromic behaviors under external stimuli. We also provide insights into current achievements, limitations, and major challenges as well as future opportunities, aiming to inspire further investigation in this field in the near future. We expect this review to inspire more innovative research on SFCSs and their advanced applications so as to promote further development of smart materials and devices.

Mechanofluorochromic Properties of 1,4-Diphenylanthracene Derivatives with Hypsochromic Shift

Several types of 1,4-diphenylanthracene derivatives 1-4 were prepared, and their photophysical properties were observed in the solid and solution states. Interestingly, the CN-group-substituted 1,4-diphenylanthracene derivative 2 was found to exhibit a higher fluorescence quantum yield (ϕf = 0.71) in the solid state than in the solution state, probably due to the formation of an intermolecular Ar-CN⋯H-Ar hydrogen bond and antiparallel type locked packing structure in the solid state. Furthermore, for some derivatives, an increase in the fluorescence quantum yield was observed in the PMMA film (1 wt%) over both the solid state and the solution state. More interestingly, some of the 1,4-diphenylanthracene derivatives exhibited unusual mechanofluorochromic properties with a "hypsochromic shift" in luminous color depending on the substituents of the phenyl group, and with the derivatives having CF3, OMe, CN, and two F substituents (1d-1f, 2-4) showing a significant luminous color change with a "hypsochromic shift" after grinding. However, no change in the luminous color was observed for the derivatives having H, Me, and one F substituent (1a-1c), and especially for some of the CN-substituted derivatives, a reversible luminous color change with a "hypsochromic shift" was observed, probably due to the formation of an antiparallel type packing structure. These "hypsochromic" anthracene derivatives could probably be utilized as new mechanofluorochromic materials.

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Multicolor Adjustable B-N Molecular Switches: Simple, Efficient, Portable, and Visual Identification of Butanol Isomers

As intelligent probes, dynamic and controllable molecular switches are useful tools for probing and intervening in life processes. However, the types and properties of molecular switches are still relatively single and often can only make two actions: "off" and "on". Therefore, the development of novel molecular switches with multiple colors and multiple instructions is very challenging. Herein, we propose a novel strategy based on the instability of the Lewis acid-base pair (boron (B) and nitrogen (N)), such as introducing the Schiff base (C═N) group into the aminoborane skeleton and preparing the novel molecular switches BN-HDZ and BN-HDZ-N. These two molecules were found to have good multicolor fluorescence switching capability for methanol. Surprisingly, the compound BN-HDZ-N shows unprecedented visual identification for the butanol isomers and could be made into a portable strip for simple and rapid visual identification of the four isomers of butanol, promising an alternative to conventional Lucas reagents. This provides a novel strategy for the design and fabrication of novel multicolor-tunable molecular switches with visual identification of isomers.

Aggregation-induced emission of a bis(imino)acenaphthene zinc complex with tetraphenylethene units

Using bis(imino)acenaphthene (BIAN) zinc(II) and palladium(II) complexes with tetraphenylethene (TPE) units as bulky aryl groups, Zn-2 and Pd-2 have been designed and developed, and their photophysical properties in solution and in the solid state have been investigated. Both in solution and in the solid state Zn-2 and Pd-2 show two photoabsorption bands in the ranges of 300 nm to 350 nm and 450 nm to 600 nm, which are assigned to the π-π* transition originating from both the TPE units and naphthalene units and the intraligand charge transfer (ILCT) between the TPE units and the BIAN unit, respectively. Density functional theory (DFT) calculations demonstrated that for Zn-2 the highest occupied molecular orbitals (HOMO) are localized on the TPE units, while the lowest unoccupied molecular orbitals (LUMO) are localized on the BIAN unit, leading to the appearance of a photoabsorption band on the ILCT. The emission from Zn-2 was quenched in solution, but appeared as phosphorescence at around 600 nm by photoexcitation at the ILCT band in the solid state as well as in the aggregated state, which was formed by the addition of n-hexane as a poor solvent to the dichloromethane (DCM) solution. The aggregate formation of Zn-2 in the DCM/n-hexane (10 wt%/90 wt%) solution was confirmed by the Tyndall scattering and scanning electron microscopy (SEM) measurements, demonstrating the aggregation-induced emission (AIE) characteristics of Zn-2. On the other hand, Pd-2 was non-emissive in the solid state and in the aggregated state as well as in solution. Moreover, the DCM-inclusion complexes of Zn-2 and Pd-2 were obtained and their photophysical properties were investigated. It was found that the photoluminescence quantum yield (Φ_PL-solid) values of Zn-2 and Zn-2-DCM in the solid state are less than 1%. Single-crystal X-ray structural analysis of Zn-2-DCM revealed the absence of intermolecular π-π interactions. Consequently, it was suggested that the low Φ_PL-solid value of Zn-2 is mainly due to the radiationless relaxation of the excitons by dynamic rotation of the phenyl groups of the TPE units, even in the solid state and in the aggregation state.

A ratiometric fluorescent dye for detection of Lys and Arg and its bioimaging in live cells and zebrafish larvae

A ratiometric and pH-sensitive fluorescent dye named IDE was applied to the detection of argine and lysine from common amino acids and exploited to monitor the Lys and Arg levels in living cells and zebrafish larvae successfully. IDE will be a useful fluorescence indicator of pH changes by Lys and Arg.

A highly selective red-emitting fluorescent probe and its micro-nano-assembly for imaging endogenous peroxynitrite (ONOO-) in living cells

Endogenous peroxynitrite plays a very important role in the regulation of life activities. However, validated tools for ONOO^- tests are currently insufficient. We designed a fluorescent probe TPA-F-NO₂ with a low fluorescence background in water based on the D-π-A structure for the imaging of endogenous ONOO^- in living cells. TPA-F-NO₂ can realize the naked eye detection of ONOO^- due to the obvious color change. TPA-F-NO₂ has the advantages of large stokes shift, high signal-to-noise ratio, high selectivity and sensitivity. The quantitative detection can be achieved in the range of 0-14 μM ONOO^-. Due to its solvatochromic characteristics, TPA-F-NO₂ has the potential to be used in OLEDs and other fields. In addition, 4-methylumbelliferone has a wide range of anticancer effects as an inhibitor of hyaluronic acid. We prepared TPA-MU-NPs by assembling TPA-F-NO₂ and 4-methylumbelliferone. It also endows TPA-MU-NPs with ONOO^- imaging function and anti-proliferation effect on breast cancer cells and other cells. This 'probe-drug' assembly strategy provides ideas for the design and optimization of dual-functional probes.

Carbazole-based aggregation-induced phosphorescent emission-active gold(I) complexes with various phosphorescent mechanochromisms

A series of carbazole-containing gold(I) complexes modified with different substituents were successfully designed and synthesized, and their molecular structures were characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. The aggregation-induced behaviors of these gold(I) complexes were studied by ultraviolet/visible and photoluminescence spectroscopy. Meanwhile, their mechanical force-responsive emissive properties were also investigated via solid-state photoluminescence spectroscopy. Interestingly, all these gold(I)-based luminogenic molecules were capable of exhibiting aggregation-induced phosphorescent emission phenomena. Furthermore, their solids of three gold(I) complexes displayed contrasting mechano-responsive phosphorescence features. More specifically, trifluoromethyl or methoxyl-substituted luminophores 1 and 3 demonstrated mechanochromic behaviors involving blue-shifted phosphorescence changes, and their mechanoluminochromic phenomena were reversible. However, the solid-state phosphorescence of phenyl-substituted luminophor 2 was not sensitive to external mechanical force.

dl-Serine Covalently Ornamented and Ln3+-Incorporated Arsenotungstates with Fast-Responsive Photochromic and Photoinduced Luminescent Switchable Behaviors

Three isostructural dl-serine covalently functionalized and multinuclear lanthanide (Ln³⁺)-embedded arsenotungstates, K₂[{As₄W₄₄O₁₃₇(OH)₁₈(H₂O)₂(dl-Ser)₂}{Ln₂(H₂O)₄(dl-Ser)}₂{Ln(H₂O)₇}₂]·70H₂O (Ln = Sm (1), Eu (2), and Gd (3); dl-Ser = C₃H₇NO₃), were prepared, where the centrosymmetric [{As₄W₄₄O₁₃₇(OH)₁₈(H₂O)₂(dl-Ser)₂}{Ln₂(H₂O)₄(dl-Ser)}₂]^8- polyanion consists of two {As₂W₁₉O₅₉(OH)₈(H₂O)}^6- fragments, integrated with a two-dl-serine-ornamented [W₆O₂₃(OH)₂(dl-Ser)₂{Ln₂(H₂O)₄}₂]^8- segment. In addition, the photochromic transformation of solid-state compounds 1-3 was observed from colorless to blue after a UV illumination of 4 min, and the decay process lasted as long as ∼20 h in the dark. The coloration kinetic half-life (t_1/2) values of compounds 1, 2, and 3 were calculated to be 0.597, 0.920, and 0.723 min, respectively. Furthermore, the luminescent properties and energy migration from arsenotungstates and organic chromophores to Sm³⁺ and Eu³⁺ ions in 1 and 2 have been intensively investigated. Further analysis manifests that 1 possesses an effective luminescent switchable behavior, triggered by its fast-responsive photochromism effect.

A Cost-Effective Way to Produce Gram-Scale 18O-Labeled Aromatic Aldehydes

Obtaining ¹⁸O-labeled organic substances is of great research importance and also an extremely challenging work. In this work, depending on the reversed Knoevenagel reaction, ¹⁸O-labeled aromatic aldehydes (3a-3x) are successfully obtained with high total yields (52-72%) and sufficient ¹⁸O abundance (90.90-96.09%).

Tetraphenylethene-Modified Colorimetric and Fluorescent Chemosensor for Hg2+ With Aggregation-Induced Emission Enhancement, Solvatochromic, and Mechanochromic Fluorescence Features

A tetraphenylethene (TPE)-modified rhodanine derivative was successfully designed and prepared, and this luminophor showed intramolecular charge transfer nature from the TPE unit to the rhodanine-3-acetic acid unit. Interestingly, this luminogen not only exhibited typical aggregation-induced emission enhancement (AIEE) behavior but also showed good cell imaging performance. Remarkably, this AIEE-active TPE-containing rhodanine derivative possessed noticeable solvatochromic fluorescence effect involving multiple fluorescent colors of green, yellow-green, yellow, orange, and red. Meanwhile, this fluorescigenic compound displayed reversible mechanochromic fluorescence behavior based on the mutual transformation of between stable crystalline and metastable amorphous states. On the other hand, this multifunctional fluorophor could selectively and sensitively detect Hg2+ in an acetonitrile solution. Furthermore, this chemosensor could also be used to detect Hg2+ on test paper strips.

Tetraphenylethene–anthracene-based fluorescence emission sensor for detection of water with photo-induced electron transfer and aggregation-induced emission characteristics

As a fluorescent sensor for water over a wide range from low to high water content regions in organic solvents, we have designed and developed a PET (photo-induced electron transfer)/AIE...

Dark to bright fluorescence state by inter-connecting fluorophores: concentration-dependent blue to NIR emission and live cell imaging applications

Interconnected AIEgens produced concentration dependent tunable emission from blue to NIR.

Luminescent polymorphic crystals: mechanoresponsive and multicolor-emissive properties

Polymorphic organic crystals that can switch their photophysical properties in response to mechanical stimuli are highlighted.

Development of a New Type of Multi-Functional Mechanochromic Luminescence Materials by Infusing a Phenyl Rotator into the Structure of 3,4-diphenylmaleic anhydride

Mechanochromic luminescence (MCL) materials have attracted increasing attention due to their versatile functions in many fields. In this work, based on the structure of 3,4-diphenylmaleic anhydride (BPMA, Mei et. al,...

Achieving Molecular Fluorescent Conversion from Aggregation-Caused Quenching to Aggregation-Induced Emission by Positional Isomerization

In this work, we synthesized a pair of positional isomers by attaching a small electron-donating pyrrolidinyl group at ortho- and para-positions of a conjugated core. These isomers exhibited totally different fluorescent properties. PDB2 exhibited obvious aggregation-induced emission properties. In contrast, PDB4 showed the traditional aggregation-caused quenching effect. Their different fluorescent properties were investigated by absorption spectroscopy, fluorescence spectroscopy, density functional theory calculations and single-crystal structural analysis. These results indicated that the substituent position of the pyrrolidinyl groups affects the twisted degree of the isomers, which further induces different molecular packing modes, thus resulting in different fluorescent properties of these two isomers. This molecular design concept provided a new accurate strategy for designing new aggregation-induced emission luminogens.

Colorimetric and Fluorescent Dual-Signal Chemosensor for Lysine and Arginine and Its Application to Detect Amines in Solid-Phase Peptide Synthesis

Lysine (Lys) and arginine (Arg), as two of the most alkaline amino acids among 20 common amino acids, are closely involved in many vital biological processes and biomaterial synthesis. Abnormal levels of Lys and Arg can lead to various diseases. Although a limited number of fluorescent probes for Lys and Arg have been reported, many of them are not sensitive enough due to the moderate fluorescence signal and on-off mode. In addition, none of them were applied for detecting amine groups in solid-phase peptide synthesis. In this study, we designed and synthesized optical fluorescent probe 1 based on the benzoxadiazole fluorophore, which could undergo an accelerated hydrolysis reaction under basic conditions. Probe 1 revealed excellent selectivity toward alkaline Lys and Arg over other common amino acids with both fluorometric and colorimetric readouts. After treatment with Lys and Arg, probe 1 could emit a turn-on fluorescent response at 580 nm with a distinct color change from pink to yellow. The limit of detection for Lys and Arg was calculated to be 1.1 and 1.39 μM, respectively. We also successfully applied probe 1 for the visualization of Arg in living cells. Moreover, to the best of our knowledge, probe 1 provided the first fluorescent platform to detect -NH₂ groups in solid-phase synthesis of peptides with distinct fluorescent and colorimetric changes. We envision that the probe can provide an alternative method for the traditional Kaiser test.

Fluorescence sensors for detection of water based on tetraphenylethene–anthracene possessing both solvatofluorochromic properties and aggregation-induced emission (AIE) characteristics

TPE-(An-CHO)4 has been developed as an SFC (solvatofluorochromism)/AIEE (aggregation-induced emission enhancement)-based fluorescence sensor for detection of water over a wide range from low to high water content regions in solvents.

Self-reversible mechanofluorochromism of AIE-active C6-unsubstituted tetrahydropyrimidine derivatives

The mechanofluorochromic properties of three C6-unsubstituted tetrahydropyrimidines (THPs), namely, diethyl 1,2,3-triphenyl-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate (1), dimethyl 1,2,3-tri(4-trifluoromethylphenyl)-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate (2), and dimethyl 1,2,3-tri(3-trifluoromethylphenyl)-1,2,3,6-tetrahydropyrimidine-4,5-dicarboxylate (3), with aggregation-induced emission (AIE) characteristics were investigated. The blue-green/cyan emissions of the three THPs can be switched reversibly by a grinding–fuming/heating process, with the change in maximum emission wavelength (λ_em) up to 57 nm and the decrease of fluorescence quantum yields (Φ_F). Interestingly, the green or cyan fluorescence of the ground powder (λ_em is located at 481, 470 and 477 nm for 1b, 2 and 3, respectively) can spontaneously recover to the original blue (λ_em is located at 434, 442 and 436 nm for 1b, 2 and 3, respectively) in 1–2 d at room temperature without any external stimulation. X-ray single-crystal diffraction, powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) studies demonstrate that the conversion between the molecular packing modes is the main reason for the mechanofluorochromism and the spontaneously recoverable mechanofluorochromism relates to intermolecular hydrogen bonds. The sensitively and/or spontaneously recoverable mechanofluorochromism of these THPs is expected to have great potential in sensing, optical recording and self-healing fluorescent materials.

AIE-active THPs exhibit interesting self-reversible mechanofluorochromism. The conversion between molecular packing modes and the intermolecular H-bonds account for the mechanofluorochromism.

An engineer's introduction to mechanophores

Mechanophores (MPs) are a class of stimuli-responsive materials that are of increasing interest to engineers due to their potential applications as stress sensors. These mechanically responsive molecules change color or become fluorescent upon application of a mechanical stimulus as they undergo a chemical reaction when a load is applied. By incorporating MPs such as spirolactam, spiropyran, or dianthracene into a material system, the real-time stress distribution of the matrix can be directly observed through a visual response, ideal for damage and failure sensing applications. A wide array of applications that require continuous structural health monitoring could benefit from MPs including flexible electronics, protective coatings, and polymer matrix composites. However, there are significant technical challenges preventing MP implementation in industry. Effective strategies to quantitatively calibrate the photo response of the MP with applied stress magnitudes must be developed. Additionally, environmental conditions, including temperature, humidity, and ultraviolet light exposure can potentially impact the performance of MPs. By addressing these limitations, engineers can work to move MPs from the synthetic chemistry bench to the field. This review aims to highlight recent progress in MP research, discuss barriers to implementation, and provide an outlook on the future of MPs, specifically focused on polymeric material systems. Although the focus is on engineering MPs for bulk materials, a brief overview of mechanochemistry will be discussed followed by methods for activation and quantification of MP photo response (concentrating specifically on fluorescently active species). Finally, current challenges and future directions in MP research will be addressed.

A phenanthro[9,10-d]imidazole-based AIE active fluorescence probe for sequential detection of Ag+/AgNPs and SCN- in water and saliva samples and its application in living cells

Ag⁺ and SCN^- play extremely important roles in the fields of the physiology and environment. In this work, on the basis of phenanthro[9,10-d]imidazole derivative (DIPIP) which can exhibit the aggregation-induced emission (AIE) properties in aqueous solution, we achieved a sequential on-off-on switch for Ag⁺ and SCN^- with high selectivity and sensitivity. A remarkable fluorescence quenching effect of Ag⁺ on the probe DIPIP was observed with 1:2 stoichiometry, Subsequently, the fluorescence intensity of in situ generated DIPIP-Ag⁺ ensemble was easily switched on after the interaction between Ag⁺ and SCN^-, which was attributed to the stronger affinity of SCN^- to capture Ag⁺. In particular, the extreme limits of detection (LOD) for Ag⁺ and SCN^- in standard solutions were as low as to be 74.5 nM and 7.8 nM, respectively. Furthermore, the probe DIPIP and the DIPIP-Ag⁺ ensemble could be used to detect Ag⁺ in the real water and SCN^- in smoker saliva samples, respectively. In addition, the sequential "on-off-on" fluorescence mode of DIPIP to Ag⁺ and SCN^- were also successfully applied in living HeLa cells.

A Dual-Stimuli-Responsive Coordination Network Featuring Reversible Wide-Range Luminescence-Tuning Behavior

We herein report a new coordination network that deforms in a smooth and reversible manner under either thermal or pressure stimulation. Concomitantly, the organic fluorophores coordinatively bound to the channel in a face-to-face arrangement respond to this structural deformation by finely adapting their conformation and arrangement. As a result, the material exhibits a remarkable dual-stimuli-responsive luminescence shift across almost the entire visible region: The emission color of the crystal gradually changes from cyan to green upon heating and then to red upon pressure compression. Furthermore, each stage exhibits a linear dependence of both the emission maximum and intensity on the stimulus and is fully reversible.

A Versatile Naphthalimide-Sulfonamide-Coated Tetraphenylethene: Aggregation-Induced Emission Behavior, Mechanochromism, and Tracking Glutathione in Living Cells

A tetraphenylethene (TPE) derivative substituted with a sulfonyl-based naphthalimide unit (TPE-Np) was designed and synthesized. Its optical properties in solution and in the solid state were investigated. Photophysical properties indicated that the target molecule, TPE-Np, possessed aggregation-induced emission (AIE) behavior, although the linkage between TPE and the naphthalimide unit was nonconjugated. Additionally, it exhibited an unexpected, highly reversible mechanochromism in the solid state, which was attributed to the change in manner of aggregation between crystalline and amorphous states. On the other hand, a solution of TPE-Np in a mixture of dimethyl sulfoxide/phosphate-buffered saline was capable of efficiently distinguishing glutathione (GSH) from cysteine and homocysteine in the presence of cetyltrimethylammonium bromide. Furthermore, the strategy of using poly(ethylene glycol)-polyethylenimine (PEG-PEI) nanogel as a carrier to cross-link TPE-Np to obtain a water-soluble PEG-PEI/TPE-Np nanoprobe greatly improved the biocompatibility, and this nanoprobe could be successfully applied in the visualization of GSH levels in living cells.

A near-infrared fluorescent probe for monitoring leucine aminopeptidase in living cells

A novel water-soluble near-infrared fluorescent probe (CHMC-M-Leu) for specific monitoring of LAP in vitro and in vivo.

Mechanofluorochromic behaviors of triphenylamine functionalized salicylaldimine difluoroboron complexes

The solid-state emission of D–A type difluoroboron complexes is tuned by external forces.

Remarkable pressure-induced emission enhancement based on intermolecular charge transfer in halogen bond-driven dual-component co-crystals

A series of two-component co-crystals driven by IN interactions based on the bipyridine (BIPY) chromophore with one among three different co-former building blocks, iodopentafluorobenzene (IPFB), 1,4-diiodotetrafluorobenzene (DITFB) and 1,3,5-trifluoro-2,4,6-triiodobenzene (IFB), were prepared and analysed via infared spectroscopy and single-crystal X-ray diffraction. By comparing the IN distances in the co-crystal structures, we found that the higher the -F ratio in the building blocks the closer the contact of the IN bond, enhancing the intermolecular interactions in these co-crystals as well. That is, the positive electrostatic potential on the iodine atom(s) in the co-formers was enhanced by the presence of strong electron-withdrawing groups. The distinct spectroscopic behaviours (fluorescence and Raman spectra) among the two-component BIPY co-crystal systems in response to hydrostatic pressure were also investigated. Interestingly, the fluorescence of BIPY-DITFB presented intriguing abnormal evolution from dark to bright, suggesting a new charge transfer state due to the decreased intermolecular distance and the enhanced IN interactions. Theoretical simulations by Materials Studio also showed the shortened IN distance and the increased angle of C-IN, evidencing the enhanced IN interactions. In contrast, BIPY-IFB showed only slightly enhanced fluorescence intensity at 550 nm consistent with BIPY-DITFB. Once the pressure was relieved, both the Raman and fluorescence spectra for BIPY co-crystal systems entirely self-recovered. Remarkable emission enhancement in a solid-state co-crystal has been rarely reported in previous publications and in fact, this study paves a unique way for designing and developing novel stimuli-responsive photo-functional materials.

Smart composite films of nanometric thickness based on copper-iodine coordination polymers. Toward sensors

One-pot reactions between CuI and methyl or methyl 2-amino-isonicotinate give rise to the formation of two coordination polymers (CPs) based on double zig-zag Cu2I2 chains. The presence of a NH2 group in the isonicotinate ligand produces different supramolecular interactions affecting the Cu-Cu distances and symmetry of the Cu2I2 chains. These structural variations significantly modulate their physical properties. Thus, both CPs are semiconductors and also show reversible thermo/mechanoluminescence. X-ray diffraction studies carried out under different temperature and pressure conditions in combination with theoretical calculations have been used to rationalize the multi-stimuli-responsive properties. Importantly, a bottom-up procedure based on fast precipitation leads to nanofibers of both CPs. The dimensions of these nanofibres enable the preparation of thermo/mechanochromic film composites with polyvinylidene difluoride. These films are tens of nanometers in thickness while being centimeters in length, representing smaller thicknesses so far reported for thin-film composites. This nanomaterial integration of CPs could represent a source of alternative nanomaterials for opto-electronic device fabrication.

Investigation of supramolecular interaction in 4, 4'-bipyridine crystal by hydrostatic pressure spectroscopies

The luminescence and structural changes of 4, 4'-bipyridine in the crystal and powder forms under the effect of high pressure applied by a diamond anvil cell has been investigated through the fluorescence and Raman spectroscopies. In its single crystal structure, the 4, 4'-bipyridine molecules are paralleled arranged with the identifiable CH⋯N and π⋯π interactions among molecules. However, in the powder form, these intermolecular interactions nearly diminish. The 4, 4'-bipyridine crystal shows the obvious bathochromic-shifting of the emission band, which is different from the powder sample that displays a fixed luminescent band during compression. Additionally, the Raman bands of them both show shifts to higher wavenumbers as different degrees. The detailed peak assignments are performed based on the theoretical calculation through B3LYP method. Comparisons in spectral behaviors between the crystal and powder under compression show the crystal form exhibits a superior mechanochromic performance relative to the powder one, because the intermolecular interactions in the crystal form play dominating roles and they can be easily tuned along with pressure in such a highly ordered structure compared to the powder form. The relation investigation between property and supramolecular interactions not only makes deeper understanding in the mechanochromic mechanisms of 4, 4'-bipyridine, but also gives a helpful reference for the molecular designs of coordination polymers and co-crystals with 4, 4'-bipyridine involved.

Highly Sensitive Ratiometric Self-Assembled Micellar Nanoprobe for Nitroxyl and Its Application In Vivo

Nitroxyl (HNO) is a derivative of nitric oxide (NO) that plays an essential role in various biological and pharmacological events. Until now, the in situ trapping and specific detection of HNO in living samples is still challenging. In this project, we fabricated a novel BODIPY-based micellar nanoprobe for monitoring nitroxyl in vitro and in vivo in ratiometric mode in aqueous solution. The probe (P-BODIPY-N) contains an asymmetrical BODIPY dye for fluorescent signaling and a diphenylphosphinobenzoyl as the trigger moiety; then we encapsulated P-BODIPY-N into the hydrophobic interior of an amphiphilic copolymer (mPEG-DSPE) and prepared a novel BODIPY-based micellar nanoprobe: NP-BODIPY-N. As far as we know, this probe is the first reported ratiometric fluorescent nanoprobe for HNO, which exhibits ultrasensitivity, high selectivity, and good biocompatibility. Above all, this nanoprobe shows favorable cellular uptaken and was successfully used to detect intracellular HNO released by Angeli's salt in living cells and zebrafish larvae. These results indicate that our newly designed nanoprobe will provide a promising tool for the studies of HNO in living system.