Donor-acceptor Stenhouse Adducts Research Articles

Self-adaptive photochromism.

Organisms with active camouflage ability exhibit changeable appearance with the switching of environments. However, manmade active camouflage systems heavily rely on integrating electronic devices, which encounters problems including a complex structure, poor usability, and high cost . In the current work, we report active camouflage as an intrinsic function of materials by proposing self-adaptive photochromism (SAP). The SAP materials were fabricated using donor-acceptor Stenhouse adducts (DASAs) as the negative photochromic phases and organic dyes as the fixed phases (nonphotochromic). Incident light with a specific wavelength induces linear-to-cyclic isomerization of DASAs, which generates an absorption gap at the wavelength and accordingly switches the color. The SAP materials are in the primary black state under dark and spontaneously switch to another color upon triggering by transmitted and reflected light in the background. SAP films and coatings were fabricated by incorporating polycaprolactone and are applicable to a wide variety of surfaces.

Crowding for Confinement: Reversible Isomerization of First-Generation Donor-Acceptor Stenhouse Adduct Derivatives in Water Modulated by Thermoresponsive Dendritic Macromolecules.

Mimicking nature, the reversible isomerization of hydrophobic dyes in aqueous solutions is appealing for bio-applications. Here, we report on the reversible isomerization of first-generation solvatochromic donor-acceptor Stenhouse adducts (DASAs) in water within dendritic matrices, realized either through the dendronization of DASAs or the incorporation of DASA pendants into dendronized copolymers. These dendritic macromolecules contain three-fold dendritic oligoethylene glycols (OEGs), which afford the macromolecules water-solubility and unprecedented thermoresponsive behavior. The thermoresponsive behavior of both dendronized DASAs and dendronized copolymers is dominated by the peripherals of dendritic OEGs. However, the hydrophilicity of the acceptor from DASA moieties also play a role in mediating their thermal phase transitions, and more importantly, tailor the hydrophobic interactions between dendritic OEGs and DASA moieties. Intriguingly, dendritic topologies contribute confinement to encapsulate the DASA moieties through crowding effects, and cooperative interactions from the crowded dendritic OEGs modulate the DASA moieties with different isomerization in aqueous media. The thermally induced collapse of dendritic OEGs, accompanied by the aggregation of dendritic macromolecules, leads to the formation of hydrophobic domains, which exert enhanced crowding effects to efficiently encapsulate the DASA moieties. Compared to the low molar mass of dendronized DASAs, thermally collapsed dendronized copolymers can efficiently retard the hydration of DASA pendants through cooperation between neighboring dendritic OEGs and afford the DASA pendants with better confined microenvironments to mediate their isomerization recovery by up to 90% from a cyclic charged (hydrophilic) state into a noncharged (hydrophobic) linear state in water. This dendritic confinement exhibits excellent fatigue resistance after several cycles of alternating photo-irradiation and thermal annealing at elevated temperatures.

Reconfigurable Visible Light-Driven Liquid Crystalline Network Showing Off-Equilibrium Motions Enabled by Mesogen-Grafted Donor-Acceptor Stenhouse Adducts.

Liquid crystalline network (LCN)-based soft actuators have opened up great opportunities to fabricate emerging and intriguing smart materials, serving as potential building blocks for intelligent soft robotics. Endowing LCN actuators with complex responsive behaviors to enhance their intelligence is both challenging and highly demanded. Herein, Donor-Acceptor Stenhouse Adducts (DASAs) molecules with rod-like mesogen and the polymerizable group are judiciously designed and synthesized, which is strong-colored at linear form and de-coloration at cyclic form after visible light. In the colored state, the DASA presents a striking photothermal effect that is capable of driving the motions of LCN film. Upon visible light irradiation, the DASA becomes colorless, making the diminishing photothermal effect. The light-gated switching of the photothermal effect renders the LCN films to be reconfigurable and perform off-equilibrium motions. The varying glass transition temperature of LCN matrix endowing tunable isomerization rates of DASAs and the equilibrium balance of photo- and thermal-isomerization at different temperatures in LCN-P-DASA film mainly guiding the off-equilibrium or stable motions, providing high adjustability of the novel visible light-driven LCN actuators. The multiply modulated LCN-P-DASA film holds great potential in constructing complex visible light-driven soft actuators based on the synergetic effect and interactions of photochemical and photothermal effects.

Integrated Sensing Platform Validated for the Efficient and On-Site Screening of Amine-Containing Illicit Drugs.

Efficient and reliable technologies for the on-site detection of illicit drugs are important in drug-facilitated crime investigations. However, the development of such technologies is challenging. Based on the synthetic optimization, introducing a boron ester functional group to the two furanic indicators endows the stimulus-responsive properties synergistically. The ring-opening reaction of the indicators in the presence of amine-containing illicit drugs generated well-known donor-acceptor Stenhouse adducts, accompanied by strong color changes. A small-size and lightweight laminated sensor was integrated based on the outstanding ratiometric variations of the two active furanic indicators. A prototype platform was fabricated equipped with a circuit control, a mini pump, and a signal processing system. A user-friendly detection and efficient screening of amine-containing illicit drugs, including phenethylamines, amphetamines, cathinones, and tryptamines in the liquid states were conducted. The ratiometric response of the sensor was linear in the concentration range of 2.1-10.6 μg·mL-1 for methamphetamine·HCl and methcathinone ·HCl. The detection limits for the two illicit drugs at the sublevel (ng·mL-1) were found to be 8.4 and 9.0 ng·mL-1, respectively. Double-blind field tests and different illicit drugs were evaluated with good screening capability. Successful trials showed the potential applications of the developed prototype platform for efficient and on-site analytical determination.

Precisely regulation of photochromism via absorption-induced photoreaction attenuation and light intensity dependence for time-resolved asymmetric encryption

With the growing need for secure information storage, encryption materials are required to be designed with high information capacity, easy to prepare, and hard to decode. Here, donor–acceptor Stenhouse adducts (DASAs), known for their straightforward synthesis, are used to develop a new time-resolved asymmetric encryption strategy, enhancing information capacity. The photoswitching property of DASAs is regulated by the intensity of initial absorbance and the intensity of light irritation. Besides, we recognize the relationship between the intensity of initial absorbance and photoswitching rate constant is caused by the absorption-induced photoreaction attenuation (AIPA). By rationally regulating the photo-bleching time of DASAs, the information can be sequentially revealed (colored state) or concealed (bleached state) in the desired temporal order. As a result, a quick response (QR) code label for practical application and a multi-level encoding scheme for sophisticated asymmetric encryption have been proposed. Specifically, the advanced asymmetric encryption technique employs layer sequence and light intensity as private keys, diverging from traditional public key systems. Information is sequentially displayed over time. The accurate information can only be revealed at the correct temporal dimension (layer sequence) and the appropriate decoding parameter (light intensity), both of which are precisely controlled by AIPA. This study not only unveils an approach to time-resolved asymmetric encryption using DASAs, enhancing the security and capacity of information storage, but also paves the way for the development of high-security encryption materials that are both highly efficient and resistant to unauthorized decoding efforts.

Supramolecular assemblies of amphiphilic donor-acceptor Stenhouse adducts as macroscopic soft scaffolds.

In the design of photoharvesting and photoresponsive supramolecular systems in aqueous medium, the fabrication of amphiphilic photoswitches enables a noninvasive functional response through photoirradiation. Although most aqueous supramolecular assemblies are driven by high-energy and biodamaging UV light, we have previously reported a design of amphiphilic donor-acceptor Stenhouse adducts (DASAs) controlled by white light. Herein, we present a series of DASA amphiphiles (DAs) with minor structural modifications on the alkyl linker chain length connecting the DASA motif with the hydrophilic moiety. The excellent photoswitchability in organic medium and the photoresponsiveness in aqueous medium, driven by visible light, were investigated by UV-vis absorption spectroscopy. The assembled supramolecular nanostructures were confirmed by electron microscopy, while the supramolecular packing was revealed by X-ray diffraction analysis. Upon visible-light irradiation, significant transformations of the DA geometry enabled transformations of the supramolecular assemblies on a microscopic scale, subsequently disassembling macroscopic soft scaffolds of DAs. The current work shows promising use for the fabrication of visible-light-controlled macroscopic scaffolds, offering the next generation of biomedical materials with visible-light-controlled microenvironments and future soft-robotic systems.

Photoactivation of Millimeters Thick Liquid Crystal Elastomers with Broadband Visible Light Using Donor-Acceptor Stenhouse Adducts.

Light-responsive liquid crystal elastomers (LCEs) are stimuli-responsive materials that facilitate the conversion of light energy into a mechanical response. In this work, a novel polysiloxane-based LCE with donor-acceptor Stenhouse adduct (DASA) side-chains is synthesized using a late-stage functionalization strategy. It is demonstrated that this approach does not compromise the molecular alignment observed in the traditional Finkelmann method. This easy, single-batch process provides a robust platform to access well-aligned, light-responsive LCE films with thickness ranging from 400µm to a 14-layer stack that is 5mm thick. Upon irradiation with low-intensity broadband visible light (100-200mW cm-2), these systems undergo 2D planar actuation and complete bleaching. Conversely, exposure to higher-intensity visible light induces bending followed by contraction (300mW cm-2). These processes are repeatable over several cycles. Finally, it is demonstrated how light intensity and the resulting heat generation influences the photothermal stationary state equilibrium of DASA, thereby controlling its photoresponsive properties. This work establishes the groundwork for advancement of LCE-based actuators beyond thin film and UV-light reliant systems.

Development and characterization of amino donor-acceptor Stenhouse adducts

Donor-acceptor Stenhouse adducts (DASAs) are molecular photoswitches spurring wide interest because of their dynamic photophysical properties, complex photoswitching mechanism, and diverse applications. Despite breakthroughs in modularity for the donor, acceptor, and triene compartments, the backbone heteroatom remains static due to synthetic challenges. We provide a predictive tool and sought-after strategy to vary the heteroatom, introduce amino DASA photoswitches, and analyze backbone heteroatom effects on photophysical properties. Amino DASA synthesis is enabled by aza-Piancatelli rearrangements on pyrrole substrates, imparting an aromaticity-breaking rearrangement that capitalizes on nitrogen’s additional bonding orbital and the inductive properties of sulfonyl groups. Amino DASA structure is confirmed by single crystal X-ray diffraction, the photochromic properties are characterized, and the photoswitch isomerization is investigated. Overall, the discovered pyrrole rearrangement enables the study of the DASA backbone heteroatom compartment and furthers our insight into the structure-property relationship of this complex photoswitch.

Sustainable Harnessing of Waste Polycarbonate for Synthesizing Activated Furans to Generate Stenhouse Adducts on Polymer Surface.

Plastics are versatile materials, offering lightweight, durable, and affordable solutions across various industries. However, their non-degradable nature poses challenges by end of their life. This study presented an innovative carbonyl extraction method to utilize waste poly(bisphenol A carbonate) (PC) as reaction precursor to synthesis of activated furan as precursor for photoswitchable Stenhouse adducts. This innovative chemical strategy not only generated N,N'-functionalized barbiturates but also provided an eco-friendly and cost-effective alternative to traditional synthesis methods. The method presented hereby not only promotes sustainability by repurposing waste polycarbonate as carbonyl equivalent under green conditions but also yielded reusable bisphenol A (BPA). Furthermore, the derived activated furans exhibited their functionality by forming colored donor-acceptor Stenhouse adducts (DASAs) on aminated polymer surfaces. This work demonstrated a transition from a linear plastics economy toward a circular one, highlighting the potential of plastic waste as a resource for creating materials with improved properties.

Robust Red-Absorbing Donor-Acceptor Stenhouse Adduct Photoswitches.

Donor-Acceptor Stenhouse Adduct (DASA), a class of push-pull negative photochrome, has received large interest lately owing to its versatile synthesis, modularity and excellent photoswitching in solutions. From a technological perspective, it is imperative for this class of photoswitches to work robustly in solid state, e. g. thin films. We feature a molecular framework for the optimized design of DASAs by introducing a new thioindoline donor (D3) and assessing its performance against known 2nd generation indoline-based donors. The systematic structure-function investigations suggest that to achieve robust reversible photoswitching, a ground state with low charge separation is desired. DASAs with stronger electron donors and a larger charge separation in the ground state result in a low population of the photothermalstationary state (PTSS) and reduced photostability. The DASA with thioindoline donor (D3A3) seems to be a special case among the donor series as it causes a red shift (ca. 15 nm), however with less polarization of the ground state and marginally better photostability as compared to the unsubstituted 2-methyl indoline (D1A3). We also emphasize the consideration of the key additional factors that can modulate the red-light photoswitching properties of DASA chromophores in polymer thin films, which might not be dominant in homogenous solution state.

Reversible isomerization of donor-acceptor Stenhouse adduct derivatives in water through dendritic confinement

Reversible isomerization of donor-acceptor Stenhouse adduct derivatives in water through dendritic confinement

Polymer Mechanochemistry on Reactive Species Generated from Mechanochemical Reactions†

Comprehensive SummaryPolymer mechanochemistry on reactive species has attracted more and more attentions over the past 20 years, as the mechanochemical generation of reactive species has a great potential in developing different polymeric materials for various purposes, such as stress detection, self‐healing, self‐strengthening, controllable degradation and release of small molecules. In this review, we first discuss the recent progress on polymer mechanochemistry of the reactive species that are generated from the mechanochemical reactions of mechanophores. Five types of reactive species, including radical, zwitterion, ionic, carbene and neutral intermediates, and their applications were reviewed in detail. Since mechanochemical reactions are sensitive to the mechanophore structure and polymer framework, we then discuss how mechanophore isomerism, polymer structure, polymer attachment point, and polymer architecture influence the mechanophore activation. At last, we provide our perspectives on the polymer mechanochemistry of reactive species. Key ScientistsIn the 1930s, a seminal work by Staudinger showed that the molecular weight of poly(styrene) reduced after mastication. However, polymer mechanochemistry mainly focused on the destructive effects of mechanical force, until Moore reported that the azo‐mechanophore was cleaved selectively upon sonication in 2005. Afterwards, his group also found that mechanical force changed the reaction pathway of benzocyclobutene and made spiropyran display purple color under stress. In 2009, Sijbesma revealed that metal–NHC could be used as a latent catalyst to catalyze transesterification and polymerization. Subsequently, the Craig group disclosed the special mechanical reactivity of perfluorocyclobutane in 2011 and examined the influence of polymer backbone on the reactivity of epoxides in 2012. Later, they also reported that the lever‐arm effect enhanced gDBC or gDCC mechanochemistry. Since 2015, Otsuka's group has developed a series of mechanophores that generated various carbon radicals and showed different colors under mechanical force. De Bo subsequently investigated the effect of regio‐ and stereochemistry on the reactivity of furan–maleimide adduct in 2017, and he examined the different mechanisms of the mechanical activation of tetrafluorobenzene–NHC (N‐heterocyclic carbene) adduct in 2020. During that time, the Choi group explored the influence of polymer architecture on the mechanophore activation, and Robb's group utilized a furan‐maleimide adduct to achieve the release of different small molecules. In 2020, Göstl and Herrmann employed the scission of the disulfide within polymers to release drugs and reporting molecules by ultrasound, and the Chen group also investigated the mechanochemistry of diselenides which afforded selenium radicals. In 2021, Boydston's group realized the “flex‐activation” of NHC‐carbodiimide to release NHC small molecules. Recently, the Chen group achieved multistate mechanochromism by combining two Rh structures together through a conjugated connector. In addition, Robb designed a furan‐maleimide adduct to mechanically give a donor–acceptor Stenhouse adduct that reacted with different amines to display various colors. This review has focused on the chemistry of reactive species that are generated from mechanochemical reactions.

Programmable Encryption Based on Photochromism of Spiropyrans and Donor–Acceptor Stenhouse Adducts

AbstractImproving information security is a persistent challenge for conventional secrecy approaches such as single and double encryption. In this work, programmable encryption is reported, involving multiple stimuli to independently control different encrypted information, to boost data security. The linear‐cyclic isomerization of donor–acceptor Stenhouse adducts (DASAs) and spirocyclic‐merocyanine (SC‐MC) isomerization of spiropyrans (SPs) on paper substrate surface are optimized by integration of ester‐contained functional molecules, making them be controlled by light irradiation and heat. By controlling the sequence of three inputs (UV light, visible light, heat), the hybrid encrypted message combining DASAs and SPs exhibits distinct outputs. The encrypted message can be recorded in various forms including characters, text, and figures. Because of the multiplied number of outputs, this method offers a straightforward and powerful solution for safeguarding data in different contexts, which enhances clarity and effectiveness, ensuring resistance to tampering and counterfeiting of the encrypted information.

Enhancing solid-state photochromic performance of Stenhouse Adducts doped in bulk polymers by C3-Symmetric multipolar design

Here, we introduce a C3-symmetric molecular design strategy to develop a brand-new visible-light organic photoswitch, named tri-branched multipolar Stenhouse Adduct (TMSA). After doping TMSA into low glass transition polymers (i.e. thermoplastic urethane, TPU) via simple blending and solution casting, the resultant composite films exploit unique geometric and electronic effects of TMSA to afford markedly-improved photoswitching performance compared to those doped with dipolar donor-acceptor Stenhouse Adduct (DASA) counterparts with suppressed solid state photochromism. Importantly, they display good fatigue resistance over 50 photo-discoloration/thermal-recovery cycles with slow degradation, surpassing those literature-reported composites involving various DASAs (<30 cycles). As revealed by combined experiment and computation studies, the multi-dimensional electronic coupling in multipolar TMSA facilitates the thermal cyclization and non-planar branched structures of TMSA afford large free space in polymers for efficient molecular isomerization, while the promoting effect on TMSA isomerization induced by ester-rich polymer micro-environments is more pronounced relative to DASA counterpart.

A DASA displaying highly efficient and rapid reversible isomerization within sustainable nano/micro capsules: one step closer to sustainability.

Donor-acceptor Stenhouse adducts (DASAs), derived from bio-based furfural, demonstrate reversible isomerization when exposed to light and heat, positioning them as attractive candidates for sustainable smart materials. However, achieving efficient and rapid isomerization in high bio-content solid-state matrices, especially under mild conditions, remains a significant hurdle due to restricted molecular mobility and limited matrix options. To address this, we developed a novel solid matrix in the form of sustainable nano/micro capsules, which boast the highest bio-content reported to date (57%). Composed of polymethylmethacrylate (PMMA) and a lauric-stearic acid eutectic mixture (L-SEM), these capsules facilitate highly efficient and rapid reversible isomerization of a third-generation DASA (DASA-1). Remarkably, the system achieves 84% forward and 90% reverse isomerization under mild temperatures, significantly enhancing the material's photo-switching capabilities. This advancement not only addresses the critical challenge of isomerization within high bio-content solid matrices but also opens broader possibilities for the application of bio-based DASAs in environmentally friendly technologies, such as color-rich rewritable papers. By innovating in the design of sustainable smart materials, this work has the potential to extend the utility of DASAs across various scientific fields, contributing to the global shift towards a low-carbon, environmentally sustainable society.

Complete kinetic and photochemical characterization of the multi-step photochromic reaction of donor-acceptor Stenhouse adducts.

Donor-acceptor Stenhouse adducts (DASA) are negative photochromic compounds exhibiting a multi-step photoisomerization mechanism. Previous studies have described a first photoactivated step, followed by a thermally controlled one. This study emphasizes the key role of the intermediate species, using high-rate acquisition photokinetic absorption spectroscopy. We have investigated the multi-step processes at different temperatures and irradiation power values. For the first time, we have combined our experimental setup with a three-species photokinetic model to determine the kinetic constants and quantum yields of each step of a DASA compound. Finally, we have identified the key role of the intermediate species, showing that double irradiation experiments allow the tuning of the photochromic reaction.

Characteristics and long-term kinetics of an azobenzene derivative and a donor-acceptor Stenhouse adduct as orthogonal photoswitches.

Light-triggered molecular switches are extensively researched for their applications in medicine, chemistry and material science and, if combined, particularly for their use in multifunctional smart materials, for which orthogonally, i.e. individually, addressable photoswitches are needed. In such a multifunctional mixture, the switching properties, efficiencies and the overall performance may be impaired by undesired mutual dependences of the photoswitches on each other. Within this study, we compare the performance of the pure photoswitches, namely an azobenzene derivative (Azo) and a donor-acceptor Stenhouse adduct (DASA), with the switching properties of their mixture using time-resolved temperature-dependent UV/VIS absorption spectroscopy, time-resolved IR absorption spectroscopy at room temperature and quantum mechanical calculations to determine effective cross sections, switching kinetics as well as activation energies of thermally induced steps. We find slightly improved effective cross sections, percentages of switched molecules and no increased activation barriers of the equimolar mixture compared to the single compounds. Thus, the studied mixture Azo + DASA is very promising for future applications in multifunctional smart materials.

Enriched switching in a donor-acceptor Stenhouse adduct via reversible covalent bonding.

We have utilized reversible covalent bonding to expand the accessible states of a molecular switch. Introducing a hydroxyl group onto the donor moiety of a donor-acceptor Stenhouse adduct (DASA) imparts an acidity response by forming an oxazolidine ring through intramolecular nucleophilic addition. Furthermore, we observed distinct color changes under cryogenic conditions, extending the thermal responsiveness beyond the cyclization equilibrium observed at elevated temperatures. These unique responses present promising prospects for diverse applications compared to traditional photoinduced binary isomerization.

Dynamic effects on the nonlinear optical properties of donor acceptor stenhouse adducts: insights from combined MD + QM simulations.

The second-order nonlinear optical (NLO) responses of a donor-acceptor stenhouse adduct (DASA) are investigated by using a computational approach combining molecular dynamics simulations and density functional theory (DFT) calculations. Specific force fields for the open and closed photoswitching forms are first parameterized and validated according to the Joyce protocol, in order to finely reproduce the geometrical features and potential energy surfaces of both isomers in chloroform solution. Then, DFT calculations are performed on structural snapshots extracted at regular time steps of the MD trajectories to address the influence of the thermalized conformational dynamics on the NLO responses related to hyper-Rayleigh scattering (HRS) experiments. We show that accounting for the structural dynamics largely enhances the HRS hyperpolarizability (βHRS) compared to DFT calculations considering solely equilibrium geometries, and greatly improves the agreement with experimental measurements. Furthermore, we show that the NLO responses of the NLO-active open form are correlated with the bond order alternation along the triene bridge connecting the donor and acceptor moieties, which is rationalized using simple essential state models.

Anti-counterfeiting fiber system with near-infrared wavelength selectivity based on photothermal and thermochromic dyes.

Anti-counterfeiting (ACF) technology plays a crucial role in distinguishing genuine products from counterfeits, as well as in identity verification. Moreover, it serves as a protective measure for safeguarding the rights of individuals, companies, and governments. In this study, a high-level ACF technology was developed using a color-conversion system based on the photothermal effect of near-infrared (NIR) wavelengths. Diimonium dye (DID), which is a photothermal dye, was selected because it is an NIR absorbing dye with over 98% transparency in the visible light (vis) region. Due to the photothermal properties of DID, the temperature increased to approximately 65 °C at 1064 nm and 39 °C at 808 nm, respectively. Additionally, we employed a donor-acceptor Stenhouse adduct dye, a thermochromic dye, which exhibits reversible color change due to heat (red color) and light (colorless). Our ACF technology was applied to the brand-protecting fiber utilizing the difference in photothermal temperature according to the NIR wavelength. We successfully implemented anti-counterfeit clothing using alphabet K labels that could distinguish between genuine and counterfeit products by irradiating with specific NIR wavelengths.