Photoswitching in a Liquid Crystalline Pt(II) Coordination Complex.

Photoswitching of photoluminescence has sparked tremendous research interests for super-resolution imaging, high-security-level anti-counterfeiting, and other high-tech applications. However, the excitation of photoluminescence is usually ready to trigger the photoswitching process, making the photoluminescence readout unreliable. Herein, we report a new photoswitch by the marriage of spiropyran with platinum(II) coordination complex. Viable photoluminescence can be achieved upon excitation by 480 nm visible light while the photoswitching can be easily triggered by 365 nm UV light. The feasible photoswitching may be benefited from the formed liquid crystalline (LC) phase of the designed photoswitch as a crystalline spiropyran is normally unable to implement photoswitching. Compared to the counterparts, this LC photoswitch can show distinct and reliable apparent colors and emission colors before and after photoswitching, which may promise the utility in high-security-level anti-counterfeiting and other advanced information technologies.

Regulating Gelation and Luminescence Behaviors of Single Pyridine-Functionalized Cyanostilbene via Metal Ions.

Luminescent metal-organic gels (LMOGs) have gained much attention due to their crucial role in visual recognition and information encryption. However, it is still a challenge to simplify the design of ligands and enrich the stimuli responses in LMOGs simultaneously. Herein, although a single pyridine ligand cannot form gel alone, after coordination with metal ions, two kinds of LMOGs have been obtained with pyridine-metal complexes, where metal ions can act as cogelators and regulate luminescence of the pyridine-functionalized cyanostilbene ligand at the same time. The effects of metal types on the fluorescence emission color, the fluorescence quantum yield, the fibril network, and the assembly mode of the gel have been investigated systematically. In addition, two competitive ligands were used to regulate the fluorescence and phase transition of the gel. Finally, the logic gates and the information encryption and decryption have been successfully constructed. This kind of material is expected to be applied to fluorescence display, advanced information encryption, high-tech anticounterfeit, and so forth.

A quadruple-stimuli responsive supramolecular hydrogel constructed from a poly(acrylic acid) derivative and ß-cyclodextrin dimer.

The fabrication of stimulus-responsive supramolecular hydrogels as smart materials has attracted much attention in recent years. However, the multi-stimuli responsiveness often requires complicated chemical synthesis and rational molecular design. Herein, a quadruple-stimuli responsive supramolecular hydrogel was designed through the host-guest interaction between a ß-CD dimer and a methoxy-azobenzene (mAzo) and ferrocene (Fc) grafted poly(acrylic acid) derivative, as well as through the electrostatic interaction of negatively charged carboxyl side groups. Owing to the dynamic properties of the host-guest and electrostatic interactions, reversible sol-gel transition can be triggered by various stimuli, including temperature, light irradiations, pH changes and chemical redox reagents. As a result, the release of rhodamine B loaded in the hydrogel can be accelerated by green light irradiation, oxidizing agents and low pH, demonstrating potential applications in biomedical materials.

Balancing Compatibility and Gelability for High-Performance Cholesteric Liquid Crystalline Physical Gels.

Liquid crystalline physical gels (LCPGs) have attracted increasing interest because of their mechanical properties and stimulus-response behaviors. However, due to their gelator properties such as thermal stability, gelation capability, and compatibility in liquid crystals, development of LCPGs with high performances still remains a huge challenging task. Herein, four novel gelators ((l)-PH, (d)-PH, (l)-P2H, and (d)-P2H) based on 1,4-benzenedicarboxamide phenylalanine derivatives containing one or two ethylene glycol groups have been designed and synthesized. It is found that the ethylene glycol group plays a significant role in improving the compatibility between the gelator and the liquid crystal. All of the prepared compounds can form stable LCPGs in P0616A. In particular, the storage modulus of LCPG with 9.0 wt % of (l)-PH with one ethylene glycol unit is higher than 106 Pa, which is similar to SmC gels and advantageous over previously reported nematic LCPGs. Furthermore, the prepared gels display a strong Cotton effect with hand-preferred twisted fiber networks and the self-assembled aggregates of (l)-PH can induce P0616A to form a cholesteric fingerprint structure. Thus, these low molecular weight gelators provide a strategy to construct high-performance cholesteric LCPGs for the realization of LC device applications.

Extending Conjugation of Linear Cyanostilbene Derivatives via a Pyridine Moiety for Multi-Stimuli-Responsive Fluorescence Organogels.

In the design of effective gelators with aggregation-induced emission behavior, amide and cholesterol moieties are generally used to provide multiple driving forces for gelation. In this work, a series of linear cyanostilbene gelators with a pyridine moiety and different lengths of the alkoxyl group, i.e., CSpy-Cn, have been synthesized through nucleophilic substitution and Knoevenagel reaction. The direct connection of pyridine extends the conjugation of the cyanostilbene moiety, while the alkoxyl group can regulate the solubility of the compounds so that the compounds can serve as gelators for common solvents such as acetonitrile, dimethyl sulfoxide, and ethanol at ultra-low concentrations. At the same time, the cyanostilbene group makes the compounds undergo photoisomerization and emit fluorescence under UV light, while the pyridine group can serve as an acid-base responsive group due to easy protonation. The gels can respond to temperature, light, and organic acid/base. The fluorescence intensity and color can reversibly change during the gel-sol transitions. Finally, a thin film based on the CSpy-C8 xerogel has been prepared and utilized as a multi-stimuli-responsive fluorescence display for information storage and anti-counterfeiting.

NIR-Cleavable and pH-Responsive Polymeric Yolk-Shell Nanoparticles for Controlled Drug Release.

Responsive drug release and low toxicity of drug carriers are important for designing controlled release systems. Here, a double functional diffractive o-nitrobenzyl, containing multiple electron-donating groups as a crosslinker and methacrylic acid (MAA) as a monomer, was used to decorate upconversion nanoparticles (UCNPs) to produce robust poly o-nitrobenzyl@UCNP nanocapsules using the distillation-precipitation polymerization and templating method. Poly o-nitrobenzyl@UCNP nanocapsules with a robust yolk-shell structure exhibited near-infrared (NIR) light-/pH-responsive properties. When the nanocapsules were exposed to 980 nm NIR irradiation, the loaded drug was efficiently released by altering the shell of the nanocapsules. The photodegradation kinetics of the poly o-nitrobenzyl@UCNP nanocapsules were studied. The anticancer drug, doxorubicin hydrochloride (DOX), was loaded at pH 8.0 with a loading efficiency of 13.2 wt %. The Baker-Lonsdale model was used to determine the diffusion coefficients under different release conditions to facilitate the design of dual-responsive drug release devices or systems. Additionally, cytotoxicity studies showed that the drug release of DOX could be efficiently triggered by NIR to kill cancer cells in a controlled manner.

Two-Color Cholesteric Liquid Crystalline Gels for Reversible Writing and Erasing Information Encryption.

Bright structural color derived from the unique helical superstructure of cholesteric liquid crystals (CLCs) has attracted much attention. In addition, fluorescence color is an intrinsic emission upon excitation, which can be observed often under UV light. However, it is a challenge to combine the fluorescence and structural colors to construct a self-supporting system at the same time. In this work, a photoresponsive cyanostilbene-based gelator (CSpy-C10) is synthesized, which emits blue fluorescence in LC. CSpy-C10 can gel LCs and further construct thermo-/photoresponsive CLC physical gels. The structural color of the CLCs, fluorescence, and mechanical properties of the gels can be independently regulated due to the separation of the chiral unit and photoresponsive unit with aggregation-induced emission behavior. Finally, the reversible information encryption including writing and erasing based on the changes in fluorescence are explored. This kind of two-color material can be applied in the fields ranging from information encryption, fluorescent display to high-tech anticounterfeiting.

Apolipoprotein L Domain Containing 1 Inhibits Tissue Factor to Impede Thrombus Formation in a Rat Model of Deep Vein Thrombosis via Activating PI3K/Akt Pathway.

BACKGROUND: Deep venous thrombosis (DVT) is one of the major health problems worldwide. Apolipoprotein L domain containing 1 (APOLD1) was reported to be downregulated in DVT. The present study intended to investigate whether APOLD1 affects thrombus formation in a rat model of DVT. METHODS: The rat model of DVT was established by inferior vena cava (IVC) stenosis. At 6 hr, 12 hr, 24 hr, and 48 hr after IVC stenosis, the gross IVC with thrombus was dissected and observed. Then, the rats were preinjected with the lentiviral overexpression vector, APOLD1-LVs, 1 hr before IVC stenosis, to evaluate the influence of APOLD1 on thrombosis in rats. The serum levels of D-dimer and TAT as well as the content of TF in IVC tissues were detected by enzyme-linked immunosorbent assay (ELISA). RESULTS: IVC stenosis resulted in thrombus formation in rats, increased serum levels of D-dimer and TAT, and decreased APOLD1 expression. APOLD1 overexpression inhibited in vivo thrombosis, reduced serum levels of D-dimer, and downregulated tissue factor (TF) activity and level. APOLD1 overexpression also increased p-PI3K and p-Akt protein levels. CONCLUSIONS: APOLD1 suppresses thrombus formation in a rat model of DVT via downregulating TF expression by activating the PI3K/Akt pathway.

Helix Induction and Inversion of Polymeric Foldamer Regulated by the Single Enantiomers.

Generally, a single enantiomer can induce a foldamer into a preferred-handed helix, while another condition is required for the helical inversion. Herein, it is found that the helix induction and subsequent inversion of poly(m-phenylene diethynylene)-based foldamer bearing aza-18-crown-6 pendants (Poly-1) can be realized by increasing the concentration of sterically hindered l-amino acid perchlorate salts. When the amount of chiral enantiomers is small, one enantiomer tends to complex with two non-adjacent aza-18-crown-6 rings via three N+ H···O hydrogen bonds in a sandwich mode. Notably, the transition dipole moment is perpendicular to the aza-18-crown-6 ring, so that the induced helical chirality in Poly-1 backbone is opposite to the chirality of enantiomers. When the amount of chiral enantiomers is large enough, each aza-18-crown-6 is occupied by one enantiomer, which causes the transition dipole moment in a parallel direction to aza-18-crown-6 ring. In this case, the increased steric hindrance can facilitate the inversion of screw sense of Poly-1 backbone, which is directed by chiral center of enantiomers. As a result, a helix inversion has been achieved successfully. This work not only provides a novel strategy for regulating the two-stage folded helical conformations by the single enantiomers, but opens a window to develop chiral recognition materials.

Injectable Thermosensitive Iodine-Loaded Starch-g-poly(N-isopropylacrylamide) Hydrogel for Cancer Photothermal Therapy and Anti-Infection.

Although photothermal therapy (PTT) can effectively eliminate tumors, the normal tissues near tumors are inevitably damaged by heat and infected by bacteria, which greatly limits the therapeutic effect. In this work, an injectable thermosensitive hydrogel based on iodine-loaded starch-g-poly(N-isopropylacrylamide) (PNSI) is developed to overcome this problem. FTIR, 1 H NMR, and UV-vis spectra confirm the graft copolymerization of poly(N-isopropylacrylamide) with starch and the formation of "iodine-starch" complex. Transmission electron microscope images show PNSI polymer self-assembles into regular spherical nanogel with a size of ≈50 nm. The concentrated nanogel dispersion is a sol at room temperature and transforms to hydrogel at body temperature. Under NIR laser irradiation for 10 min, the ΔT of the nanogel dispersion approachs about 20 °C with excellent thermal stability and high cytotoxicity due to the photothermal effect of the "iodine-starch" complex. After intratumor injection, this injectable hydrogel efficiently inhibites the tumor growth under 808 nm laser irradiation. Furthermore, it can also suppress Staphylococcus aureus infection in the wound post-PTT due to the release of iodine, which promotes wound healing. Therefore, this injectable thermosensitive "iodine-starch" composite hydrogel with advantages of good biocompatible and easy preparation possesses potential application for tumor photothermal therapy and antibacterial infection.

Configuration-Dependent Liquid Crystal and Gel Behaviors of Tetraphenylethene-Containing Main-Chain Copolyesters.

The construction of aggregation-induced emission-active (AIE-active) gelators with liquid crystal properties remains a challenge. Moreover, the effects of AIE configuration on liquid crystal, gel and AIE behaviors in one system are unclear. Herein, two main-chain liquid crystalline copolyester gelators with a single configuration of AIEgen TPE, mesogen biphenyl, and pendent amide groups are synthesized through melt polycondensation. Both copolyesters display smectic phase, while E-P20 possesses a wider temperature range of liquid crystal and a narrower layer distance owing to the more serious nonlinear "defect" of Z-TPE than E-TPE units. In addition, E-P20 and Z-P20 can form AIE-active gels with the minimum gelation concentration (MGC) values of 10 and 4 wt% in ethyl acetate mainly via hydrogen bonds between the pendent amide groups, respectively. These AIE-active gels show potential applications in temperature sensor, information storage, and so on.

Light regulation and long-lived stability of RGB colors in cholesteric liquid crystal physical gels via a mixing strategy.

Photo-responsive cholesteric liquid crystals (CLCs) have attracted much attention due to the dynamic tunability of their unique helical superstructure. However, it is still a challenge to endow the mechanical properties and to regulate the reflection colors at the same time. In this work, a simple strategy is developed for the construction of thermo-responsive CLC physical gels via the direct mixing of photo-responsive dopants and a gelator with nematic LCs. The reflection colors of CLCs and the mechanical properties of gels can be independently regulated due to the separation of the photo-responsive chiral group from the gelator. In addition, the CLC reflection colors can be regulated via visible light in the range of RGB with long-lived thermal stability. Finally, the information storage properties of this kind of CLC gel have been investigated.

High-Performance Photochromic Hydrogels for Rewritable Information Record.

Rewritable information record materials usually demand not only reversibly stimuli-responsive ability, but also strong mechanical properties. To achieve one photochromic hydrogel with super-strong mechanical strength, hydrophobic molecule spiropyran (SP) has been introduced into a copolymer based on ion-hybrid crosslink. The hydrogels exhibit both photoinduced reversible color changes and excellent mechanical properties, i.e., the tensile stress of 3.22 MPa, work of tension of 12.8 MJ m-3 , and modulus of elasticity of 8.6 MPa. Moreover, the SP-based Ca2+ crosslinked hydrogels can be enhanced further when exposed to UV-light via ionic interaction coordination between Ca2+ , merocyanine (MC) with polar copolymer chain. In particular, hydrogels have excellent reversible conversion behavior, which can be used to realize repeatable writing of optical information. Thus, the novel design is demonstrated to support future applications in writing repeatable optical information, optical displays, information storage, artificial intelligence systems, and flexible wearable devices.

Intrinsically Visible Light-Responsive Liquid Crystalline Physical Gels Driven by a Halogen Bond.

Photoresponsive physical gels using liquid crystals (LCs) as solvents have attracted great interest owing to their potential applications. But, current investigations mainly focus on UV light, which is not environment-friendly enough. On the other hand, the halogen bond is a novel tool for constructing supramolecular gels because of good hydrophobicity, high directionality, tunable strength, and large size of halogen atoms. Herein, to construct an LC physical gel with both the advantages of a halogen bond and visible light response, azopyridine-containing Azopy-C10 is chosen as a halogen bond acceptor, while 1,2-bis(2,3,5,6-tetrafluoro-4-iodophenyl)diazene is selected both as the halogen bond donor and for the intrinsically visible light response. Such a binary gelator can self-assemble in the anisotropic solvent of nematic LC 5CB to form an LC physical gel. It experiences the gel-to-sol transition by green light irradiation. As the gelator concentration increases, the saturation voltage increases, but the switch-off time decreases. The combination of the halogen bond and controllable visible light-responsive LC physical gel provides the feasibilities of manipulating these smart soft materials.

Wholly Visible-Light-Responsive Host-Guest Supramolecular Gels Based on Methoxy Azobenzene and ß-Cyclodextrin Dimers.

Much attention has been paid to construct photoresponsive host-guest supramolecular gels; however, red-shifting the responsive wavelength remains a formidable challenge. Here, a wholly visible-light-responsive supramolecular gel was fabricated through the host-guest interaction between a ß-cyclodextrin (ß-CD) dimer and a tetra-ortho-methoxy-substituted azobenzene (mAzo) dimer (binary gelator) in DMSO/H2O (V/V = 8/2). The minimum gelation concentration of the low-molecular-weight binary gelator was 6 wt % measured via the tube inversion method. The substituted methoxy groups shifted the responsive wavelengths of trans-mAzo and cis-mAzo to the green and blue light regions, respectively. The host-guest interaction between mAzo and ß-CD as the driving force for gelation was confirmed using the 1H-NMR and 2D 1H NOESY spectra. The supramolecular gel showed good self-supporting ability with a storage modulus higher than 104 Pa. The release of Rhodamine B loaded in the gel as a model drug could be controlled by green light irradiation. We envisioned the potential applications of the wholly visible-light-responsive supramolecular compounds ranging from biomedical materials to smart materials.

Reversible Redox Switching of Concurrent Luminescence and Visual Color Change Based on Lanthanide Metallogel.

The development of reversible redox supramolecular gels capable of concurrent luminescence switch and visible color change with the facile redox process has always been an intriguing challenge. A redox-responsive supramolecular lanthanide metallogel with strong luminescence and yellow color is obtained via coordination interaction between 3,5-dinitrosalicylic acid (DNSA) and europium (Eu3+). Upon the addition of TiO2 to the prepared gel (DNSA/Eu3+ gel), the oxidation process of the gel (DNSA/Eu3+/TiO2 gel) can be easily achieved by UV irradiation. The DNSA/Eu3+/TiO2 gel exhibits a concurrent reversible "on-off" luminescence and color change in response to redox stimuli. The DNSA/Eu3+/TiO2 gel shows a concurrent quench of luminescence and a color change from yellow to red when the gel was stimulated by the reductant. Upon UV irradiation, the luminescence and color of the reduced DNSA/Eu3+/TiO2 gel restored to its initial state due to the strong oxidation ability of hydroxyl radicals derived from photocatalytic oxidation of TiO2. The results of UV-vis and mass spectroscopy indicated that the reversible redox responsiveness of DNSA/Eu3+/TiO2 gel depends on the reversible oxidation-reduction reactions of DNSA. Moreover, DNSA/Eu3+/TiO2 gel remains stable because the morphology of the gel had no change during the redox process. Exemplarily, the application of DNSA/Eu3+/TiO2 gels to achieve luminescent patterning was investigated. The results demonstrated that the prepared metallogel has potential applications in the fields of writable materials, anticounterfeiting, sensors, and others.

Visible light-triggered gel-to-sol transition in halogen-bond-based supramolecules.

Photoresponsive supramolecular gels have aroused continuous attention because of their extensive applications; however, most studies utilize UV light, which inevitably brings about some health and environmental issues. The halogen bond is an important driving force for constructing supramolecules due to its high directionality, tunable strength, good hydrophobicity, and large size of the halogen atoms. Yet, it still remains a formidable challenge to utilize halogen bonds as a driving force to fabricate a visible light responsive gel. In this work, to fabricate such a gel, azopyridine-containing Azopy-Cn (n = 8, 10, 12) was selected as a halogen bond acceptor, while 1,2-bis(2,3,5,6-tetrafluoro-4-iodophenyl)diazene (BTFIPD) was chosen as both the halogen bond donor and visible light responsive moiety. The visible light response of BTFIPD resulted from the significant separation of n-π* energy levels between trans and cis isomers due to the introduction of an electron-withdrawing group (fluorine) to azobenzene at the ortho-position. Interestingly, the gel exhibited a good gel-to-sol transition behavior upon green light irradiation. At the same time, the morphologies varied from uniform narrow flakes to broad sheets with increasing illumination time. We provide an environmentally-friendly visible light-triggered method to regulate the phase transition of supramolecular materials in applications ranging from energy conversion to information storage.

Visible Light Rewritable and Long-Lived Colors in Cholesteric Liquid Crystals: A Facile Co-Doping Strategy.

Photoresponsive cholesteric liquid crystals (CLCs) are able to selectively reflect colors upon light exposure. Yet, it still remains a formidable challenge to realize simultaneous rewriting and long-life color in CLCs using visible light. Herein, guided by time dependent density functional theory (TD-DFT) computation, an octafluorinated binaphthyl azobenzene is synthesized to achieve the fast response and long-life color upon visible light exposure. Subsequently, based on the solubility parameter, uniform CLCs are formulated through a facile co-doping strategy. Interestingly, the CLCs change reflection colors from blue to green, red, and then into the near infrared region in seconds upon 550 nm light illumination. The completely reversible process is readily accessable upon 450 nm irradiation. More importantly, each color is independently stable for ≈24 h in the dark.

Photomodulated Morphologies in Halogen Bond-Driven Assembly during Gel-Sol Transition.

Photoresponsive supramolecular gels with various applications are being constantly pursued; however, achieving well-defined morphology changes of gels via light irradiation remains a formidable challenge. In this study, a gel is prepared through halogen bond between azopyridine-containing Azopy-C10 and 1,4-tetrafluorodiiodobenzene. The gel exhibits gel-sol transition due to trans-cis isomerization of the azopyridine moiety upon UV irradiation. During this transition, the morphologies vary from flake to fluffy bobble-like and finally to peony-like with increasing exposure time, which is difficult to achieve in traditional assembly systems. The microstructure change is attributed to the variations of cis-isomer content and halogen-bonding strength. The supramolecular gel provides a novel method to achieve photomodulated morphologies and broadens the applications of such kind of materials, ranging from information storage to high-tech anticounterfeit.

Photomodulated Electro-optical Response in Self-Supporting Liquid Crystalline Physical Gels.

Photoresponsive liquid crystal (LC) physical gels have attracted more and more attention because of the nature of strong response via light stimulus. Although many efforts on the breaking and recovering of physical gels through photoisomerization have been focused, fast electro-optical response and high mechanical properties even upon light irradiations are difficult to achieve at the same time. In this work, two kinds of azobenzene-containing gelators (AG1 and AG2) with different terminal groups were designed and synthesized. Both gelators could induce the nematic LC P0616A self-assemble into anisotropic phase-separated LC physical gels at low contents. Their phase-transition behavior, thermal stability, microstructure, and mechanical strength were systematically studied. Compared with AG2 in P0616A, the P0616A/AG1 gels showed better mechanical property. When the gelator content was above 3 wt %, the P0616A/AG1 gels possessed good self-supporting ability with a storage modulus more than 104 Pa. Thus, the photoresponsive electro-optical properties and structures of P0616A/AG1 gels were focused in detail. It was surprising that the electro-optical response speed of the P0616A/AG1 gels could be promoted upon UV irradiation. In particular, the decay time (τoff) was only about half when compared with the initial state, whereas the gels still exhibited good self-supporting ability; also the network of the LC physical gels had no change at macro- and microstructural levels. These exciting results would open a door for the application of this material in electro-optical devices.