Donor-acceptor Stenhouse Adducts Research Articles

Ester Matters? Promoting Photoisomerization of Donor-Acceptor Stenhouse Adducts in Solid and “Burn after Reading” Encryption

Ester Matters? Promoting Photoisomerization of Donor-Acceptor Stenhouse Adducts in Solid and “Burn after Reading” Encryption

Acidochromism of donor-acceptor Stenhouse adducts in organic solvent.

First generation DASA derivatives can be reversibly isomerized from the coloured, open form to the colourless, closed isomer upon protonation, thus behaving as acidochromic compounds in halogenated organic solvent.

Different Conical Intersection Profiles between the First and Second Generation of Donor-Acceptor Stenhouse Adducts Accounting for Their Largely Different Z-E Photoisomerization Rates

Different Conical Intersection Profiles between the First and Second Generation of Donor-Acceptor Stenhouse Adducts Accounting for Their Largely Different Z-E Photoisomerization Rates

Improving the kinetics and dark equilibrium of donor-acceptor Stenhouse adduct by triene backbone design.

DFT calculations were used to find an optimal substitution site on the triene backbone of a donor-acceptor Stenhouse adduct photoswitch to tune the equillibrium and switching kinetics of DASA without modifying the donor and acceptor groups. Using this approach we demonstrate a new means to tuning DASA based photoswitches by increasing the energy of the closed form relative to the open form. To highlight the potential of this approach a new DASA derivative bearing a methyl substituent on the 5-position of the triene was synthesized and the effect of this substitution was studied using 1H NMR spectroscopy, time-dependent UV-Vis and solvatochromic analysis. The new DASA derivative shows a higher dark equillibrium, favoring the open form, and drastically faster thermal recovery than the unsubstituted derivative with the same donor and acceptor.

Donor–acceptor Stenhouse adduct formation for the simple and rapid colorimetric detection of amphetamine-type stimulants

Widespread abuse of amphetamine-type stimulants (ATS) calls for the development of reliable and rapid on-site analytical methods for their detection and quantitation. A simple, rapid, sensitive, selective, and inexpensive method for the colorimetric detection of ATS using furylidene Meldrum’s acid derivative 1 is reported herein. This colorimetric assay is based on the formation of Stenhouse adducts, through a chromogenic ring-opening mechanism upon the reaction of 1 with secondary amines, including methamphetamine (METH), 3,4-methylenedioxymethamphetamine (MDMA), and related illicit drugs. The reaction is accompanied by the formation of a new, red shifted absorption band resulting in a distinct color change from colorless to red. The utility of the colorimetric assay is demonstrated in aqueous solution, spiked drinks, and ‘ecstasy’ tablets. Detection limits of 0.36 μg·mL−1 METH and 0.57 μg·mL−1 MDMA in aqueous solution are achieved, and the naked-eye detection of ATS is also realized within 5 min in multiple matrices. Moreover, this method is resistant to interference from various pharmaceuticals, controlled substances, or common cutting agents found in illicit drugs. Paper-based portable indicators based on 1, suitable detection of ATS by agents in the field, are additionally reported.

In Silico Discovery of Multistep Chemistry Initiated by a Conical Intersection: The Challenging Case of Donor-Acceptor Stenhouse Adducts.

Detailed mechanistic understanding of multistep chemical reactions triggered by internal conversion via a conical intersection is a challenging task that emphasizes limitations in theoretical and experimental techniques. We present a discovery-based, hypothesis-free computational approach based on first-principles molecular dynamics to discover and refine the switching mechanism of donor-acceptor Stenhouse adducts (DASAs). We simulate the photochemical experiment in silico, following the "hot" ground state dynamics for 10 ps after photoexcitation. Using state-of-the-art graphical processing units-enabled electronic structure calculations we performed in total ∼2 ns of nonadiabatic ab initio molecular dynamics discovering (a) critical intermediates that are involved in the open-to-closed transformation, (b) several competing pathways which lower the overall switching yield, and (c) key elements for future design strategies. Our dynamics describe the natural evolution of both the nuclear and electronic degrees of freedom that govern the interconversion between DASA ground-state intermediates, exposing significant elements for future design strategies of molecular switches.

Fast photochromism in solid: Microenvironment in metal-organic frameworks promotes the isomerization of donor-acceptor Stenhouse adducts

The isomerization of photoresponsive molecules in the solid state is always restricted due to the intermolecular stacking. In this work, we fabricated solid powdery materials with fast and efficient photochromism by embedding donor-acceptor Stenhouse adducts (DASAs) into the nanocages of metal-organic frameworks (MOFs). Visible light irradiation (530 nm, 40 mW/cm2) induces linear-to-cyclic isomerization of DASAs in ~7.7 s with a 100% conversion efficiency, which is with the same order of magnitudes as that in solution. Meanwhile, the isomerization of loaded DASAs is fully reversible after repeated treating by visible light and heat. The microenvironment in the nanocages of MOFs is able to promote the isomerization to either linear or cyclic DASAs, which was unfold by density functional theory calculations. All in all, the solid powdery materials are further applied as additives to realize photochromism of bulk materials, which show reversible color change under visible light and heat.

808nm Near-Infrared Light-Triggered Payload Release from Green Light-Responsive Donor-Acceptor Stenhouse Adducts Polymer-Coated Upconversion Nanoparticles.

Owing to deep activation in biotissues and enhanced targeting efficiency, developing photoresponsive polymer-upconversion nanoparticles (PP-UCNPs) nanovectors has witnessed rapid growth in the past decade. However, up to date, all developed nanovectors require high-order photon processes to initiate the release of cargos. The photodamage caused by high-power near-infrared laser light may be a critical obstacle to their clinical application. Here, for the first time, by leveraging absorption-emission spectral matching between donor-acceptor Stenhouse adducts (DASA) PP and UCNPs (λex , 808nm) in the green region (≈530nm), the designed nanovector is capable of releasing cargos at a low-power 808nm excitation (0.2 W). Considering the high molar absorptivity, biobenign, and synthetic tunability of DASA, DASA PP can be utilized as an up-and-coming candidate to design and synthesize the next generation of upconversion nanovectors without photodamage.

Colorimetric Method for Instant Detection of Lysine and Arginine Using Novel Meldrum's Acid‐Furfural Conjugate

AbstractIn the past few years Meldrum's acid furfural conjugate (MAFC) have been extensively explored as starting material for the synthesis of photo switchable donor acceptor stenhouse adducts (DASA). Hereby, we have explored the interaction of MAFC with various amino acids. To our surprise, nitrogen rich amino acids like lysine and arginine interact spontaneously with MAFC to give colored adduct immediately, whereas other amino acids, including nitrogen rich histidine, didn't show any coloration. Naked eye detection of lysine in benign solvent make this reagent an attractive new entry to the collection of chemosensors for the colorimetric detection of lysine and arginine. Intense coloration corresponds to the absorption at 514 nm under UV‐Vis spectrometer. Lowest concentration of 100 μm can be detected with UV‐Vis spectrometer. NMR titrations reveals that the appearance of color is due to ring opening of a furfural that leads to the formation of conjugated triene species. Compared to previously reported chemosensors for lysine and arginine, MAFC offers advantages including simple synthesis, easy handling, high speed, low cost, good sensitivity/selectivity.

β-Amyloid Peptides Manipulate Switching Behaviors of Donor-Acceptor Stenhouse Adducts.

Molecular switching plays a critical role in biological and displaying systems. Donor-acceptor Stenhouse adducts (DASAs) is a newly re-discovered series of switchable photochromes, and light is the most used approach to control its switching behavior. In this report, we speculated that hydrophobic binding pockets of biologically relevant peptides/proteins could be harnessed to alter its switching behavior without the assistance of light. We designed and synthesized a DASA compound SHA-2, and we demonstrated that the Aβ40 species could stabilize SHA-2 in the linear conformation and decrease the rate of molecular switching via fluorescence spectral studies. Moreover, molecular dynamics simulation revealed that SHA-2 could bind to the hydrophobic fragment of the peptide and resulted in substantial changes in the tertiary structure of Aβ40 monomer. This structural change is likely to impede the aggregation of Aβ40, as evidenced by the results from thioflavin T fluorescence and ProteoStat aggregation detection experiments. We believe that our study opens a new window to alter the switching behavior of DASA via DASA-peptide/protein interactions.

Electrochemical Switching of First-Generation Donor-Acceptor Stenhouse Adducts (DASAs): An Alternative Stimulus for Triene Cyclisation

Donor-acceptor Stenhouse adducts (DASAs) are a photo-switch class that undergoes triene cyclisation in response to visible light. Herein, electrochemical oxidation is demonstrated as an effective alternative stimulus for the triene cyclisation commonly associated with photo-switching.

Effect of heteroaromatics on the photochromic properties of Bindone-Aryl SpiroCyclohexadienes

In the last decade, photochromes activated by visible light have garnered increased interest due to their ability to modulate the properties of materials via the most benign stimulus available, light. This interest has focused on the development of new photochromic classes and thorough study of how to selectively tune their properties. Currently, the dominant class arising from these efforts are Donor-Acceptor Stenhouse Adducts, which display negative T-type behavior. The recently discovered Bindone-Aryl SpiroCyclohexadienes, which display positive T-type behavior, are poised to serve as a complementary class to DASAs. Herein, we show that the spectral and kinetic characteristics of the emergent Bindone-Aryl SpiroCyclohexadiene class can be modulated via the introduction of heteroaromatic donor groups.

Encapsulation and Stabilization of a Donor-Acceptor Stenhouse Adduct Isomer in Water Inside the Blue Box: A Combined Experimental and Theoretical Approach.

We synthesized two types of donor-acceptor Stenhouse adducts (DASAs), a new type of photochromic molecules showing dual color in two different isomeric forms in solution phase, using Meldrum acid (DASA-Mel) and barbituric acid (DASA-Bar), along with a naphthalimide derivative to obtain interesting fluorescence properties. DASA-Mel was found to have fast photochromic conversion in comparison to DASA-Bar, evident from ultraviolet-visible (UV-vis) and fluorescence spectroscopic studies. The colored form of DASA-Mel was encapsulated inside the water-soluble Stoddart's blue box and became soluble in water much faster than DASA-Bar. Interestingly, the competitive encapsulation experiment showed that DASA-Mel was selectively encapsulated inside the blue box in water whereas DASA-Bar was mostly separated out from the solution after centrifugation, and this phenomenon was confirmed by 1H and DOSY NMR and mass spectroscopies. Moreover, we found through density functional theory (DFT) optimization that the open form of DASA-Mel was more stable during the encapsulation reaction in a water medium in comparison to DASA-Bar. The calculated binding energies of encapsulated DASA-Mel and DASA-Bar are -10.2 and -9.9 kcal/mol, respectively, clearly showing that the former is more stable by 0.3 kcal. Consequently, the organic macrocycle selectively separating one kind of DASA from a mixture by encapsulation in water is reported for the first time with experimental and theoretical support in the literature.

Self-assembled micelle responsive to quick NIR light irradiation for fast drug release and highly efficient cancer therapy

Upconversion nanoparticles (UCNPs) have been used for designing near infrared (NIR) light-responsive nanocarriers and controllable drug release. However, the need for long-term NIR light irradiation over hours impaired their application efficiency. Here we develop a self-assembled micelle of amphipathic polymer P-DASA which degrades via quick NIR light irradiation. UCNPs and DOX are also encapsulated in the micelle for quick drug release. P-DASA is composed of hydrophilic polyethylene glycol segment and photo-responsive hydrophobic donor–acceptor Stenhouse adduct (DASA). Only 5-min NIR irradiation causes the hydrophilicity conversion of P-DASA and the complete disruption of micelle with DOX fast release of 83.7% in 30 min to achieve highly efficient therapy. Moreover, the P-glycoprotein mediated DOX efflux is also diminished by concomitantly producing NO intracellularly. This micelle demonstrates impressive in vivo therapeutic effect, and thus provides an avenue for highly efficient cancer therapy.

Switching of second-order nonlinear response effected by different acceptors: The impacts of environment and frequency dispersion

In this work, the second-order nonlinear optical (NLO) switch features and electron transition properties for a series of donor-acceptor Stenhouse adducts (DASAs) were explored. The systems we studied contain of a given diethylamine donor and different acceptors, which can be photoinduced from open form to closed form. The calculation results show a remarkable difference in the first hyperpolarizability (β) value between two configurations for each of studied systems, revealing a conspicuous NLO switch feature. Interestingly, in the conditions of gas phase, solid phase polarization effects or frequency dispersion effects, the introduction of indandione acceptor demonstrates the most significant NLO switch feature due to the largest βopen/βclose ratio of compound 5. In general, the differences in the degree of π-electron conjugation and electron transition property between two configurations are responsible for the contrast of NLO response. Our work reveals the features of NLO switch on structure and electron transition property, which will provide some guidance for designing high performance NLO materials.

Designing of Rewritable Paper by Hydrochromic Donor-Acceptor Stenhouse Adducts.

Rewritable paper is meaningful to the recyclable and sustainable utilization of environmental resources and thus has been extensively investigated for several decades. In this work, we demonstrated an efficient and convenient strategy to fabricate rewritable paper based on reversible hydrochromism of donor-acceptor Stenhouse adducts (DASAs). The kinetics and efficiency of isomerization could be well-controlled by adjusting the surrounding temperature and humidity. Monocolored rewritable paper was prepared by coating cyclic DASA·xH2O on the paper surface. Writing, printing, stamping and patterning were realized on the rewritable paper. The information could be controllably erased by treatment in a humid atmosphere. More importantly, the rewritable paper was upgraded to multicolored by combination of two DASA materials. The color of chirography was switched by controlling the writing speed.

Nano-3D-Printed Photochromic Micro-Objects.

Molecular photoswitches that can reversibly change color upon irradiation are promising materials for applications in molecular actuation and photoresponsive materials. However, the fabrication of photochromic devices is limited to conventional approaches such as mold casting and spin-coating, which cannot fabricate complex structures. Reported here is the first photoresist for direct laser writing of photochromic 3D micro-objects via two-photon polymerization. The integration of photochromism into thiol-ene photo-clickable resins enables rapid two-photon laser processing of highly complex microstructures and facile postmodification using a series of donor-acceptor Stenhouse adduct (DASA) photoswitches with different excitation wavelengths. The versatility of thiol-ene photo-click reactions allows fine-tuning of the network structure and physical properties as well as the type and concentration of DASA. When exposed to visible light, these microstructures exhibit excellent photoresponsiveness and undergo reversible color-changing via photoisomerization. It is demonstrated that the fluorescence variations of DASAs can be used as a reporter of photoswitching and thermal recovery, allowing the reading of DASA-containing sub-micrometric structures in 3D. This work delivers a new approach for custom microfabrication of 3D photochromic objects with molecularly engineered color and responsiveness.

Visible light/Cu2+ dual triggered photochromic donor-acceptor stenhouse adducts: Synthesis, properties and applications

Light is not the only stimuli which can coverts donor-acceptor Stenhouse adducts (DASAs) from the triene to the cyclopentenone form. Here, we firstly demonstrate that Cu2+ can drive linear-to-cyclic isomerization of DASAs in acetonitrile, which increase the rate of color fading. Three different generations of DASAs (DASA-1, DASA-2, and DASA-3) have been synthesized by Knoevenagel condensation to verify the universal applicability of the mechanism by which copper ions discolor DASAs. The Job's plot of DASA-1 to Cu2+ indicated DASA-1 binds to Cu2+ with a ratio of 1:1, and the 1H NMR titration spectrum of Cu2+ on DASAs as well as the UV–Vis absorption spectra with adding Cu2+ showed that copper ions could induce the process of linear-to-cyclic isomerization of DASAs in acetonitrile. Based on this, we propose copper ions as the eraser of a DASA derived ink to achieve repeatable erasing. Furthermore, DASAs have been utilized as a Cu2+ sensor with high selectivity and sensitivity.

Using Donor–Acceptor Stenhouse Adducts to Teach Photochromism in the Undergraduate Laboratory

There has been dramatic growth in interest and research regarding organic photochromism in recent decades. Despite this, the topic is seldom addressed in the undergraduate chemistry curriculum. Herein, we present a straightforward and robust experiment for the second semester organic chemistry laboratory curriculum which combines multistep synthesis, photochromism, and optical characterization. Over the course of a three-step synthesis, students prepare both the open and closed isomers of a Donor–acceptor Stenhouse adduct. At each stage of the synthesis, the pure products are isolated by filtration and characterized by traditional means (FTIR, 1H NMR). Additionally, students collect UV–vis data on the photoisomerization process and use this to calculate kinetic parameters. An inquiry-based variant of the experiment is also presented.

Visible Light Stimulated Bistable Photo-Switching in Defect Engineered Metal–Organic Frameworks

The incorporation of photoactive donor-acceptor Stenhouse adduct (DASA) moieties into Metal-Organic Frameworks (MOFs) provides a new route to the development of visible light switching materials. Herein, a DUT-5 mixed-linker defect series was exploited to produce a derivative group of DASA-modified materials via postsynthetic modification (PSM). The photoactive MOFs exhibited conversion stimulated by visible wavelengths and were stable following multiple cycles. Thermodynamic and metastable states persisted over an extended time period.