Donor-acceptor Stenhouse Adducts Research Articles

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.

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.

Repurposing Bial’s Reaction to Engender Donor–Acceptor Stenhouse Adducts: A Computational Investigation

In pursuing novel photoresponsive materials, we computationally investigated a series of Bial’s reaction-derived Donor–Acceptor Stenhouse Adducts (BialDASAs), comparing them with a prototypical DASA compound, D1A1. We employed density functional theory to elucidate the electronic and geometric factors influencing their photochromic behaviour. Our study confirmed that BialDASA compounds display dual absorption peaks attributed to the π–π∗ transitions, distinct from the single peak of D1A1, reflecting the involvement of the acceptor group in their excited states. Moreover, minimal Bond Length Alternation (BLA) suggested a potential for extended conjugation, consistent across these compounds’ closed and open forms. Analysis of the Z to E isomerization in the excited state indicated a pathway for deactivation via conical intersection, hinting at efficient photoswitching capabilities. Furthermore, the thermodynamic profiles underscored feasible cyclization barrier heights in the ground state, augmented by solvent effects. These findings emphasis the promise of BialDASA molecules as photoswitchable entities and advance our understanding of photochemical mechanisms, providing a scaffold for further experimental validation and application development in molecular electronics and photonics.

Lewis Acid Catalyzed 4π-Electrocyclization of Donor–Acceptor Stenhouse Adducts

AbstractLewis acid catalyzed 4π-electrocyclization of Donor–Acceptor Stenhouse Adducts (DASAs) has been developed. By employing catalytic quantities of Dy(OTf)3, a highly efficient transformation of acyclic DASAs into the corresponding cyclized isomers was achieved. Notably, this transformation exhibited exceptional yields, particularly in the case of first generation DASAs. In addition, Lewis acid catalysis enabled one-pot synthesis of the cyclopentenone product from the ‘donor’ and ‘acceptor’ components.

Meldrum's Acid Furfural Conjugate MAFC: A New Entry as Chromogenic Sensor for Specific Amine Identification.

Bioactive amines are highly relevant for clinical and industrial application to ensure the metabolic status of a biological process. Apart from this, generally, amine identification is a key step in various bioorganic processes ranging from protein chemistry to biomaterial fabrication. However, many amines have a negative impact on the environment and the excess intake of amines can have tremendous adverse health effects. Thus, easy, fast, sensitive, and reliable sensing methods for amine identification are strongly searched for. In the past few years, Meldrum's acid furfural conjugate (MAFC) has been extensively explored as a starting material for the synthesis of photoswitchable donor-acceptor Stenhouse adducts (DASA). DASA formation hereby results from the rapid reaction of MAFC with primary and secondary amines, which has so far been demonstrated through numerous publications for different applications. The linear form of the MAFC-based DASA exhibits intense pink coloration due to its linear conjugated triene-2-ol conformation, which has inspired researchers to use this easy synthesizable molecule as an optical sensor for primary, secondary, and biogenic amines. Due to its new entry into amine identification, a collection of the literature exclusively on MAFC is demanded. In this mini review, we intend to present the state-of-the-art of MAFC as an optical molecular sensor in hopes to motivate researchers to find even more applications of MAFC-based sensors and methods that pave the way to their usage in medicinal applications.

Visible‐Light‐Responsive Crystalline Solids by Equipping Covalent Organic Frameworks with Donor‐Acceptor Stenhouse Adducts

Comprehensive SummaryControlling properties of crystalline solids by light remains a challenge because the lack of intrinsic structural flexibility limits the necessary molecular mobility for photoisomerization. In this work, we reported a series of visible‐light‐responsive covalent organic frameworks (COFs) by introducing donor‐acceptor Stenhouse adducts (DASAs) with various electron‐withdrawing moieties via a post‐modified strategy. The DASAs‐functionalized COFs exhibit distorted honeycomb layered topology with long‐range periodicity. The DASAs grafted on the skeletons are pointing into the nanopores of COFs, which weakens intermolecular aggregation and ensures sufficient free volume to undergo reversible isomerization between linear and cyclic states. Furthermore, the crystalline and optical properties of COFs as well as the geometrical size and hydrophilicity inside the nanopores were reversibly controlled by alternating visible light irradiation and heat. Finally, methyl violet was used as the cargo molecules to be immobilized into the nanopores of COFs, which showed fast release under controlling of visible light.

Effect of polymer host matrix on multi-stage isomerization kinetics of DASA photochromes

Molecular photoswitches provide a means for imparting synthetic structures with intrinsically logical and highly tunable photoresponsive properties. One variety of organic photoswitches known as Donor-Acceptor Stenhouse Adducts, or DASAs, are promising candidates for next generation light responsive materials because of their unique ability to stabilize three photochemically distinct isomeric states in solution, while their counterparts are strictly limited to binary state behavior. In this work, we show how polymethacrylate host matrices shift the energetic landscape of DASA relative to solution, prohibiting accumulation of an intermediate third isomeric state by decelerating critical steps in the photoswitching mechanism. Specifically, we employ a dual-wavelength, phase locked detection scheme to probe thermal isomerizations in the switching process that occur at fast (∼ms) time scales that are inaccessible by standard UV–Vis spectroscopic techniques. The results of this study provide valuable insight into the mechanism of multistate DASA reactivity and establish the foundation necessary to guide future efforts in offsetting kinetic matrix effects to enable dynamic, three state photoswitching in polymeric hosts.

Novel class of photochromic molecules exhibiting photo-switching in the solid state.

Photo-switching compounds are widely used as super-resolution imaging agents, anti-counterfeiting dyes, and molecules that are able to control drug-receptor interactions. However, advancement of this field has been limited by the number of classes of molecules that exhibit this phenomenon, and thus there are growing activities to discover new photo-switching compounds that diversify and improve current applications and include the so-called donor-acceptor Stenhouse adducts. Herein, a new class of compounds, phenylindole alkene dimers, are presented as a novel class of photochromic molecules that exhibit photo-switching in the solid state. The synthesis of a small library of these compounds allowed the tuning of their optical properties. Surfaces coated with these photo-switches can be used as writable materials in a variety of applications.

Selective control of donor-acceptor Stenhouse adduct populations with non-selective stimuli

Selective control of donor-acceptor Stenhouse adduct populations with non-selective stimuli

Nonlinear Optical Responses of Photoswitchable Donor–Acceptor Stenhouse Adducts

This work combines hyper-Rayleigh scattering (HRS) experiments performed in the NIR range (1.30 and 1.60 μm) and quantum chemical calculations to provide a comprehensive description of the second harmonic generation (SHG) responses of donor-acceptor Stenhouse adducts (DASAs). Representative derivatives of the three generations of DASAs, which differ by the nature of their electron-donating and withdrawing moieties and also include clickable species, have been synthesized and their photoswitching behavior fully characterized. The HRS measurements allow us to establish relationships between the magnitude of the SHG response of open forms and the nature of the donor and acceptor groups. The largest SHG responses are obtained for derivatives incorporating either a barbituric acid or an indanedione acceptor unit, while N-methylaniline appears as the most efficient donor group. The calculations support well the experimental data and show that high hyperpolarizabilities are associated to low excitation energies and large extent of the photoinduced intramolecular charge transfer, which enhances the dipole moment variation between the ground and first dipole-allowed electronic excited state. In addition, a complete investigation of the photoswitching kinetics of DASAs in chloroform solution shows important differences, highlighting in particular the role of the donor group on the photoswitching efficiency.

Highly Selective and Quantitative Point-of-Care Diagnostic Method for Adrenaline.

Adrenaline, also known as epinephrine, is a neurotransmitter/hormone that is an important target in diagnostics. Development of an effective method for detecting it in the presence of other neurotransmitters is a challenging task. The electrochemical and fluorescent techniques commonly used have low selectivity in distinguishing among catecholamines. Herein, a small-molecule organic probe with an activated furfural moiety is reported to exploit the nucleophilicity of epinephrine to generate a bright-colored donor-acceptor Stenhouse adduct. Among nine common neurotransmitters or their analogues, only epinephrine was found to generate a unique colour change discernible with the naked eye, whereas the other ones remain unaffected. Under various in-field detection conditions, including solution, droplet, and paper strip-based detection, the colour change were also noticeable. The low detection limit of 1.37 nM and a limit of quantitation of 4.37 nM were achieved with simple UV/Vis methods in addition to the sub-ppm level sensing under visual conditions with naked eyes. The probe could be used for practical colorimetric measurements as a point-of-care tool without any complex and expensive machinery, making this approach accessible to all. In addition, using a simple smartphone, the determination of epinephrine concentrations is possible by using machine-learning techniques.

Isomerization of DASA Molecules in the Nanopores of Metal-Organic Frameworks: What Determines Its Reversibility?

In recent years, light-responsive molecules have been incorporated in metal-organic frameworks (MOFs) to fabricate light-responsive intelligent devices, where reversible isomerization of the guest molecules in the nanopores is crucial. However, how to design a porous environment of MOFs to achieve a reversible isomerization remains unknown until now. In this work, donor-acceptor Stenhouse adducts (DASAs), a new kind of visible light responsive compound, were confined in the nanopores of different MOFs to study their isomerization upon visible-light irradiation/mild heating. We found that the polarity of the pore environment is the key to control the reversibility of isomerization of such guest molecules. Under the guidance of this principle, MIL-53(Al) was screened to investigate the proton conductivity and switching performance of the DASA-confined MOF. The proton conductance was up to 0.013 S cm-1 at 80 °C and 98 % RH, and at least 30 switching cycles were achieved thanks to the Grotthuss-type mechanism and the low polarity of MIL-53(Al) pore environment.