Multiple Stimuli-responsive Properties Research Articles

Multiple Stimuli-Responsive Color-Changing Polymer Materials for Reversible Writing and Anti-Counterfeiting.

Polymer materials with multiple stimuli-responsive properties have demonstrated many potential and practical applications. By covalently introducing spiropyran (SP1) and spirothiopyran (STP) into the polyurethane backbone, photochromic, mechanochromic, and thermally discolored polymer materials have been prepared. In this work, we report for the first time that white light (violet, blue, and green light) above a certain intensity can activate STP to green color. Based on the above discovery, the polyurethane with SP1 and STP can exhibit reversible three-color changes (brown, green, and purple) in response to four stimuli: ultraviolet irradiation, white light irradiation, mechanical stress, and heat. The color-changing polymer materials have high color contrast and excellent reversibility, and can be used for reversible writing, anticounterfeiting and information encryption, etc.

Dual responsive behaviors in fluorescence of molecular crystals based on naphthalene pyridyl derivatives

Three compounds based on naphthalene and pyridine structures with different nitrogen positions (NP-2, NP-3, and NP-4) were synthesized. Except for displaying aggregation-induced emission (AIE) properties, the solution and crystals of these compounds show reversible fluorescence changes under alternative acid and base treatments. Experimental results, including X-ray diffraction, optical spectroscopy measurements, and cross-polarized microscope characterization, suggested that compounds might undergo reversible crystal-to-crystal transition upon external acid and base stimuli. It also revealed that the position of the heteroatom nitrogen in the pyridine unit significantly affected the intra- and intermolecular interactions, leading to restricted-intermolecular motions (RIMs) that caused the AIE effect. Besides, computational calculations indicated significant changes in molecular geometries and electronic interactions between the initial states and the protonated states. An information encryption system involving activation and operation codes was established based on the multiple stimuli-responsive properties. Our work not only presents a facile way to develop multiple responsive properties in molecular crystal systems but also explores their potential as highly emissive functional dyes for future applications.

Anti-Kasha triplet energy transfer and excitation wavelength dependent persistent luminescence from host-guest doping systems

Anti-Kasha’s process in organic luminogens has attracted many attentions since its discovery. However, only limited examples of anti-Kasha’s rule have been reported and anti-Kasha triplet energy transfer (ET) is even less-touched. Benefiting from anti-Kasha’s rule, this work provided an efficient strategy to realize excitation wavelength dependent (Ex-De) afterglow in a host-guest system. The host has almost imperceptible RTP upon 365 nm excitation and guest is totally RTP inactive, while the doping host-guest system exhibits Ex-De afterglow with improved quantum yields. Anti-Kasha triplet ET process is realized from the higher excited triplet state T2 of host to the lowest excited singlet state S1 of the aggregated/unimolecular guest. ET efficiency in the doping system could be tuned by simply changing its processing methods to guide host and guest to adopt denser or looser intermolecular packing. The strategy of anti-Kasha triplet ET endows the host-guest doping system with multiple stimuli-responsive properties, including Ex-De afterglow, mechano-, and thermal-triggered afterglow behaviors. The corresponding applications of these properties are also realized in multiple information anti-counterfeiting and display.

Construction of intelligent interfaces based on stimulus-responsive hydrogels and ligand-free gold nanoparticles for electrocatalysis of isoquercitrin

In recent years, researchers have taken a keen interest in intelligent electrochemical interfaces. Nevertheless, incorporating multiple stimuli-responsive properties while ensuring a significant electrochemical response remains an interesting question. In this work, ligand-free gold nanoclusters grown on carbon nitride supports (AuNCs@N-C) were loaded on pyrolytic graphite (PG) electrode by layer-by-layer (LbL) method to obtain the {AuNCs@N-C}3 inner layers with good catalytic effect on isoquercitrin (IQ, 3-(β-d-Glucopyranosyloxy)-3′,4′,5,7-tetrahydroxyflavone). Then, the semi-penetrating stimuli-responsive hydrogel poly(N-isopropyl acrylamide)-poly(acrylic acid) (PNIPAM-PAA) was modified on the catalytic layer surface by drop-coating method. As a result, we obtained reversible electrochemical responses triggered by changes in temperature, sodium sulfate concentration, and pH. A new type of logic gate has been created by combining the difference in peak current during the stimulus response with the change in potential corresponding to the peak current. A 3-input/3-output tri-state buffer gate and a 1-to-4 demultiplexer have been designed through careful simplification, offering a fresh approach to building electrochemical pharmaceutical logic gates.

Latest Findings on Stimuli-Responsive Hydrogel Wound Dressings Applied in Diabetic Chronic Wound Repair

Diabetic chronic wounds entail enormous psychological and economic burdens on diabetic patients. Traditional types of wound dressings lack diversity in their functions and do not have sufficient adaptability to the wound environment, which makes it difficult to meet the complicated needs arising during the healing process when they are used. Stimuli-responsive hydrogels respond specifically to the special environment of the wound area, for example, temperature, pH, glucose, etc., and achieve on-demand release by loading active substances, which effectively promotes diabetic wound healing. Herein, based on the research progress in stimulus-responsive wound dressings in recent years and the relevant work of our research team, we summarized and discussed hydrogel wound dressings responsive to temperature, pH, glucose, reactive oxygen species, enzymes, and multiple stimuli. Based on the special physiological environment of diabetic wounds, hydrogels with single or multiple stimuli-responsive properties can be designed so that they can release drugs on demand and improve the microenvironment of the wound, thus meeting the specific needs of different stages of wound healing. Although stimuli-responsive hydrogels currently show excellent therapeutic potential, there is still room for further development-cells or cytokines loaded in wound dressings usually act only at specific healing stages and the timing needs to be precisely controlled in order to avoid counterproductive effects on wound healing. In addition, the construction of sensor-therapeutic integrated devices for real-time monitoring of wound biochemical indicators so that drugs are release on demand and with precision to promote wound healing is also one of the topics that deserve more attention from researchers.

Organic Crystals with Response to Multiple Stimuli: Mechanical Bending, Acid-Induced Bending and Heating-Induced Jumping.

Multiple stimuli-responsive molecular crystals are attracting extensive attentions due to their potential as smart materials, such as molecular machines, actuators, and sensors. However, the task of giving a single crystal multiple stimuli-responsive properties remains extremely challenging. Herein, we found two polymorphs (Form O and Form R) of a Schiff base compound, which could respond to multiple stimuli (external force, acid, heat). Form O and Form R have different elastic deformability, which can be attributed to the differences in the molecular conformation, structural packing and intermolecular interactions. Moreover, both polymorphs exhibit reversible bending driven by volatile acid vapor, which we hypothesize is caused by reversible protonation reaction of imines with formic acid. In addition, jumping can be triggered by heating due to the significant anisotropic expansion. The integration of reversible bending and jumping into one single crystal expands the application scope of stimuli-responsive crystalline materials.

Multiple stimuli-responsive properties of Coumarin-Salicylaldehyde Schiff Bases

Organic small-molecules of multiple stimuli-responses were widely paid attention, which can be applied in multiple fields simultaneously, such as thermal sensor, force response, pH probe, reagents for the detection of metal ion and so forth. In the present work, three novel coumarin derivatives (XDS-R) were synthesized from various salicylaldehydes containing different substituents (R = H, Cl, Br), following by investigations about their multiple stimuli-responsive properties concerning aggregation-induced emission (AIE), mechanochromism, thermochromism and pH response. Single crystals of XDS-R indicate that intramolecular hydrogen bonds cause the restriction of intramolecular vibration, leading to AIE character and mechanochromic property. Interestingly, two substituents (H, Cl) have little effect on fluorescence intensity and color, and whereas have distinguishable influences on functionalized fluorescence response. In the pH range of 2.00–8.00, only XDS-H exhibited regular pH-response, while XDS-Cl and XDS-Br showed excellent pH tolerance. Mechanochromic XDS-R is able to recover to original state under heating. A simple multilevel anticounterfeit label was made by the combination of XDS-Cl and previous-reported DDHAC without an automatic heat-inspired recovery. Combined multilevel stimuli-responsive material of XDS-Cl and previous DDHAC displayed potential application of anti-counterfeiting mark.

New shoots from old roots: multiple stimuli-responsive properties of a common tetraphenylethene derivative

Reversible tricolored mechanochromism and recyclable mechanoluminescence properties (new shoots) of a reported tetraphenylethene derivative (old roots) were explored.

Quinoline-cored Poly(Aryl Ether) Dendritic Organogels with Multiple Stimuli-Responsive and Adsorptive Properties.

Functional supramolecular gel materials have potential applications in sensors, optical switches, artificial antennae, drug delivery and so on. In this paper, quinoline-cored poly(aryl ether) dendritic organogelators were designed, synthesized and fully characterized. The gelation behaviour of the dendritic organogelator was tested in organic solvents, mixed solvents and ionic liquids. The dendron Q-G1 was found to be an efficient and versatile organogelator toward various apolar and polar organic solvents with the critical gelation concentrations (CGCs) approaching 1.2×10-2 mol/L, indicating one dendritic organogelator could immobilize 1.2×103 solvent molecules in the organogel network. Interestingly, these dendrons exhibited excellent gel formation in ionic liquids. Notably, these dendritic organogels were found to display multiple stimuli-responsive properties toward external stimuli including heat, ultrasound and shear stress, with a reversible sol-gel phase transition. In addition, the dendritic organogel could effectively adsorb heavy metals and organic dyes. The removal rate of Pb2+ was up to 20% and the adsorption rate for Rhodamine B was as high as 89%.

Amphiphilic Diazapyrenes with Multiple Stimuli-Responsive Properties.

A series of amphiphilic diazapyrenes exhibiting switchable fluorescence under the stimulus of mechanical force or water vapor are reported for the first time. Comprehensive studies of their photophysical properties in different states based on UV-Vis absorption, FL emission, FT-IR spectroscopy, and XRD analysis have revealed a stimuli-induced excimer-based sensing mechanism. The relationship between molecular structures and optical responsive properties of these diazapyrene derivatives is illustrated. Moreover, the unique fluorescent, stimuli-responsive behaviors of these diazapyrene compounds in the solid state are used to fabricate sensory films for successively and orthogonally sensing mechanical force and water vapor. In contrast to the well-established knowledge on the transformation between the pyrene monomer and excimer, our study offers valuable information about the unknown diazapyrene excimers and demonstrates their potential applications in biocompatible force sensors, data storage, and humidity sensors.

Recent developments in selenium-containing polymeric micelles: prospective stimuli, drug-release behaviors, and intrinsic anticancer activity.

Selenium is capable of forming a dynamic covalent bond with itself and other elements and can undergo metathesis and regeneration reactions under optimum conditions. Its dynamic nature endows selenium-containing polymers with striking sensitivity towards some environmental alterations. In the past decade, several selenium-containing polymers were synthesized and used for the preparation of oxidation-, reduction-, and radiation-responsive nanocarriers. Recently, thioredoxin reductase, sonication, and osmotic pressure triggered the cleavage of Se-Se bonds and swelling or disassembly of nanostructures. Moreover, some selenium-containing nanocarriers form oxidation products such as seleninic acids and acrylates with inherent anticancer activities. Thus, selenium-containing polymers hold promise for the fabrication of ultrasensitive and multifunctional nanocarriers of radiotherapeutic, chemotherapeutic, and immunotherapeutic significance. Herein, we discuss the most recent developments in selenium-containing polymeric micelles in light of their architecture, multiple stimuli-responsive properties, emerging immunomodulatory activities, and future perspectives in the delivery and controlled release of anticancer agents.

Self-healable, Eu3+-based polymeric gels containing terpyridyl groups with tunable luminescence based on ion recognition

Novel luminescent materials that change their emission colors in responding to external stimuli have attracted increasing attentions in the past decades. Herein, we report the preparation of a novel kind of Eu3+-based polymeric organogel with three networks. With dynamic coordination interactions, the organogel shows fast self-healing and adjustable fluorescent emission properties in the presence of different metal ions via coordination interaction competition effect. Dynamic coordination interaction also endows the gel with multiple stimuli-responsive properties such as water, base and acid. The multistimuli responsive fluorochromic organogel demonstrates a new way of preparing optical materials and bio-relevant sensors.

Multi-stimuli responsive novel polyimide smart materials bearing triarylamine and naphthalimide groups

Multiple stimuli-responsive smart polymers have received increasingly attention in recent years. In this work, a series of novel polyimides (PIs) bearing triarylamine and naphthalimide perssad were devised and prepared. These novel polyimides are able to respond to four different stimuli (light, pH, explosives and voltage) and perform four functions (light detectors, electrochromism, fluorescence detectors and memory devices). Furthermore, the smart materials are suitable for complicated environment. This work will open a new route for the development of novel smart materials with multi-functional and multiple stimuli-responsive properties.

Synthesis, luminescent and multiple stimuli-responsive properties of π-extended BF2 β-diketone complexes containing an acridone unit

A class of π-extended BF2 β-diketone chromophores, ADBF2-a and ADBF2-b, that containing electron donating N-butyl acridone units have been synthesized. ADBF2-a and ADBF2-b are highly fluorescent with quantum efficiencies (ΦF) close to unity in toluene. The fluorescence of ADBF2-b displays more pronounced solvatochromism and shows a twisted intramolecular charge transfer (TICT) character in polar solvent and aggregation induced emission enhancement (AIEE) behavior. Furthermore, ADBF2-b shows high contrast and sensitive acid/base induced emission “On/Off” switching that result from the reversible protonation/deprotonation of the nitrogen atom. The compounds are also highly luminescent in solid state with a ΦF value of 0.63 for ADBF2-a and 0.28 for ADBF2-b. Single crystal analysis reveals the highly rigid and planar backbone of ADBF2-a. The emission stimuli-responsive properties of the compounds in solid state have been investigated. ADBF2-a shows yellow emission (λem = 564 nm) in crystalline state while turned to be orange (λem = 586 nm) after grinding. Intriguingly, CH2Cl2 vapor fuming of the ground solid led to red emissive (λem = 624 nm) solid, which turned to original yellow color with further CH2Cl2 vapor fuming. The solid of ADBF2-b emits red (λem = 645 nm) fluorescence in crystalline state and red-shifted to λem = 680 nm for amorphous solid after mechanical grinding. The crystalline state was recovered by CH2Cl2 vapor fuming. We believe that this BF2 system will inspire the development of high luminescent solid-state materials, and provide important insights into smart stimuli-responsive properties.

MPTTF-containing tripeptide-based organogels: receptor for 2,4,6-trinitrophenol and multiple stimuli-responsive properties

A series of monopyrrolotetrathiafulvalene-tripeptide conjugates have been synthesized and investigated as new low-molecular mass organogelators. It was found that most of these compounds could immobilize low-polarity solvents readily and the gelation behaviors of these gelators showed a dependence on the amino acid residues. These organogels were thoroughly studied using various techniques including atomic force microscopy (AFM), field-emission scanning electron microscopy (FE-SEM), circular dichroism (CD) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, (1)H NMR spectroscopy, UV-Vis absorption spectroscopy and X-ray diffraction (XRD). The results showed that the cooperative interplay of hydrogen bonding, π-π stacking and SS interactions were the main driving force for the formation of the gels. Of all the organogels, the aromatic solvent gels, such as toluene gel, exhibited multiple-stimulus responsiveness towards heating, shaking, chemical redox activity and the presence of anions, thus leading to reversible sol-gel phase transitions. Most interestingly, gelation in the presence of 2,4,6-trinitrophenol (TNP) in organic solvents could be observed visually with a concomitant color change through donor-acceptor interactions. The strength of the charge-transfer interaction between gelators and TNP was proportional to the incubation time and increasing critical gelation concentration (CGC). The gels could function as efficient absorbents for potential application in removal of crystal violet and rhodamine B dyes from water.

Rational construction of gel-based supramolecular logic gates by using a functional gelator with multiple-stimuli responsive properties.

A gelator containing a sorbitol moiety and a naphthalene-based salicylideneaniline group exhibits macroscopic gel-sol behavior in response to four complementary input stimuli: temperature, UV light, OH(-), and Cu(2+). On the basis of its multiple-stimuli responsive properties, we constructed a rational gel-based supramolecular logic gate that performed OR and INH types of reversible stimulus responsive gel-sol transition in the presence of various combinations of the four stimuli when the gel state was defined as an output. Moreover, a combination two-output logic gate was obtained, owing to the existence of the naked eye as an additional output. Hence, gelator 1 could construct not only a basic logic gate, but also a two-input-two-output logic gate because of its response to multiple chemical stimuli and multiple output signals, in which one input could erase the effect of another input.

A Borinic Acid Polymer with Fluoride Ion‐ and Thermo‐responsive Properties that are Tunable over a Wide Temperature Range

A new type of smart borinic acid polymer with luminescence and multiple stimuli-responsive properties is reported. In DMSO with small amounts of water, the homopolymer PBA shows a tunable upper critical solution temperature (UCST). As the amount of water increases from 0 to 2.5 % (v/v), the UCST rises linearly from 20 °C to 100 °C (boiling point of water). Thus, the thermal responsive behavior can be tuned over a wide temperature range. Furthermore, polymer solutions in DMSO show a reversible response to fluoride ions, which can be correlated to the presence of the Lewis acidic borinic acid groups. Upon addition of fluoride, the polymer becomes soluble because the functional R2BOH groups are converted into ionic [R2BF2](-) groups, but turns insoluble again upon addition of H2O, which reverses this process.

Controllable self-growth of a hydrogel with multiple membranes

The controllable self-growth of a supramolecular hydrogel of folic acid (FA) was developed based on the conduction of transition metal ions. The growth behavior of the gel could be flexibly controlled by adjusting the ambient environmental factors such as gelator concentration, temperature and external chemical stimuli. The obtained gel was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and rheological measurements. Differential scanning calorimetry (DSC) showed that the gel possessed excellent thermal stability. A mechanism for the fibrous formation of the gel was suggested based on the experimental results of Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR) and UV-Vis spectroscopy. The gel exhibited multiple stimuli-responsive properties to changes in ligand and pH. Furthermore, the gel can be incorporated into multi-layer hydrogels in both artificial and spontaneous ways, showing the advantages of self-growth and flexible control of the gel system. This novel hydrogel and the preparation strategy may provide a new route to rationally design advanced materials for biomedical applications.