Spiropyran Research Articles

Dual-Responsive Thermally Activated Delayed Fluorescence of Spiropyran Derivatives

Dual-Responsive Thermally Activated Delayed Fluorescence of Spiropyran Derivatives

Light-Induced Quantitative and Electrical-Field-Induced Barrierless Switching of Spiropyran Derivative on Graphite Surface.

A new class of pyridine-based spiropyran (SP) shows photoinduced reversible switching between the closed SP and ring-opened merocyanine (MC). We show that a condensed crystalline monolayer of SP on graphite can be quantitatively converted to MC upon UV irradiation. In solution only ∼10% of SP can be transformed to MC because of the establishment of a photostationary state. Using an electrical field applied by a scanning tunneling microscopy (STM) tip, single molecules are reversibly switched between SP and MC forms in their condensed phases without any threshold voltage at ambient conditions. The microscopic structure of submonolayer films of SP and MC are investigated using atomic force microscopy (AFM) and STM.

Toward Mechanochromic Soft Material-Based Visual Feedback for Electronics-Free Surgical Effectors.

A chromogenically reversible, mechanochromic pressure sensor is integrated into a mininvasive surgical grasper compatible with the da Vinci robotic surgical system. The sensorized effector, also featuring two soft‐material jaws, encompasses a mechanochromic polymeric inset doped with functionalized spiropyran (SP) molecule, designed to activate mechanochromism at a chosen pressure and providing a reversible color change. Considering such tools are systematically in the visual field of the operator during surgery, color change of the mechanochromic effector can help avoid tissue damage. No electronics is required to control the devised visual feedback. SP‐doping of polydimethylsiloxane (2.5:1 prepolymer/curing agent weight ratio) permits to modulate the mechanochromic activation pressure, with lower values around 1.17 MPa for a 2% wt. SP concentration, leading to a shorter chromogenic recovery time of 150 s at room temperature (25 °C) under green light illumination. Nearly three‐times shorter recovery time is observed at body temperature (37 °C). To the best of knowledge, this study provides the first demonstration of mechanochromic materials in surgery, in particular to sensorize unpowered surgical effectors, by avoiding dramatic increases in tool complexity due to additional electronics, thus fostering their application. The proposed sensing strategy can be extended to further tools and scopes.

PH-responsive spiropyran-based copolymers and their application in monitoring and antibacterial coatings

Although many multifunctional antibacterial materials have been developed, there are few antibacterial materials that can simultaneously monitor pathogenic bacteria and sterilize efficiently. In this work, pH-responsive spiropyran-based fluorinated copolymers with antibacterial, antifouling and fluorescence performances were prepared. First, the random copolymer of methacrylic acid and 1H,1H,2H,2H-perfluorododecyl acrylate (P(MAA-co-FDA)) were synthesized by RAFT polymerization. Second, spiropyran (SP) was grafted onto P(MAA-co-FDA) to obtain the P(MAA-co-SP-co-FDA) copolymer with fluorescence property. At the third step, the remaining carboxyl groups in the grafted copolymer were complexed with protonated polyhexamethylene biguanidine salt (PHMB) to obtain the P(MAA-co-SP-co-FDA)/PHMB copolymer complex antibacterial materials. The results show that the copolymer complex coatings can effectively inhibit the adhesion of bacteria and release PHMB in a bacterial microenvironment to kill S. aureus and E. coli but remain noncytotoxic. The P(MAA-co-SP-co-FDA) copolymer or its complex with PHMB can open the ring and generate a red fluorescence under acidic conditions produced by bacterial growth and metabolism. In addition, the coatings have good biocompatibility, which may be suitable for medical devices to reduce bacterial infection in vivo and in vitro. The prepared multifunctional materials with excellent anti-adhesion, antimicrobial and fluorescence characters will have a broad application prospect in antibacterial, antifouling and monitoring of medical devices.

Light‐Responsive Circularly Polarized Luminescence Polymers with INHIBIT Logic Function

AbstractDynamically tuning the emission of circularly polarized luminescence (CPL) materials through external stimuli is fascinating because of their fundamental and application interests. In this work, light‐responsive and luminescence‐tunable CPL‐active materials are synthesized by mixing achiral helical polymer containing vibration‐induced emission (VIE) molecules and spiropyran (SP) with a chiral helical polymer. Through regulating the distinct emission of VIE molecules and the reversible photoisomerization of SP, the dynamic Förster resonance energy transfer (FRET) can be explored to reversibly control the emission color of CPL in different states after light‐controlled isomerization. This project is the first comprehensive investigation of CPL‐active materials with VIE properties. Finally, taking the advantage of the multistimuli responsive CPL signal in different states, an “INHIBIT” logic gate with CPL signal output based on the combination of control of UV/vis light irradiation time and state alternation is constructed.

Learning from Spiropyrans: How to Make Further Developments of Donor‐Acceptor Stenhouse Adducts

AbstractDonor‐acceptor Stenhouse adducts (DASAs) as a species of novel photochromic molecules, have been developing rapidly and attracting broad researchers’ sights since 2014. DASAs show visible/near‐infrared (NIR) light induced linear‐to‐cyclic isomerization and heat induced cyclic‐to‐linear isomerization, therefore they are attractive in photoresponsive hydrogels, drug delivery, cell culturing and tissue engineering. As a series of well‐known photoresponsive molecules, spiropyrans (SPs) show similar molecular properties and comparable photoswitching with DASAs. UV light triggers closed‐to‐open (also known as spirocyclic (SC)‐to‐merocyanine (MC)) isomerization of SPs, while the reversed open‐to‐closed isomerization occurs under visible light or heat. Light irradiation switches the molecular color, scale, geometry, and polarity of SPs and DASAs reversibly. Since the researches on DASAs are still in the infancy, the chemical structures, isomerization mechanisms and potential applications need to be further investigated and explored. The well‐studied SPs have important reference values to the comprehensive developments of DASAs. In the present review, we summarized, compared and discussed SPs and DASAs with regards to their molecular structures, synthesis, photoswitching and applications. We also make our perspective on the developments of DASA in future.

Photoisomerization dynamics of spiropyran: A surface-hopping investigation

In the present work, we performed a computational investigation of the photoisomerization of spiro[1,3-dihydroindole-2,2'-chromene] [spiropyran (SP)] to merocyanine. The electronic energies and wavefunctions were obtained from configuration interaction calculations, using the floating occupation molecular orbital method, in a semiempirical framework. The parameters of the semiempirical Hamiltonian were re-optimized to reproduce ab initio literature data for SP. In our dynamics simulations, we considered, besides S0, the excited states S1, S2, and S3, which are very close in energy in the Franck-Condon region. We obtained a singlet lifetime of 0.67 ps, in line with the experimental results. We found the photoisomerization quantum yield to depend on the electronic state initially populated.

Fulgide Derivative-Based Solid-State Reversible Fluorescent Switches for Advanced Optical Memory

Fulgide Derivative-Based Solid-State Reversible Fluorescent Switches for Advanced Optical Memory

Visible light-induced hydrogels towards reversible adsorption and desorption based on trivalent chromium in aqueous solution

How to detect and recover Cr(III) (Cr3+) from contaminated water through an economical and environmental way is not negligible but significant to solve serious pollution of heavy metal ions. Herein, a spiropyran [1′-(n-butyl)-3′,3′-dimethyl-6-nitrospir[chromene-2,2′-indoline] (SPBU) with negative photochromism is exploited as a visual detector for Cr3+. In contrast to positive photochromism of spiropyran derivatives, the synthesized SPBU can isomerize from colorless form spiropyran (SP) to the corresponding colored merocyanine (MC) form and further complex with Cr3+ under darkness without essential UV irradiation, providing a facile strategy enable visual detection of Cr3+ in aqueous solution. Importantly, we have synthesized SPBU-Polyethylene glyol (SPBU-PEG) hydrogels with negative photochromism via physical blending. Evidence from practical performance confirms that Cr3+ can be captured from aqueous solution under darkness and repelled from the hydrogel effectively upon visible light irradiation to achieve the regeneration of the designed adsorbent with a save-energy manner, avoiding any desorbent and secondary contamination. Additionally, the SPBU-PEG hydrogels have excellent Cr3+ selectivity and reproducibility. This work provides a significant greener way to exploit visible light responsive materials for reversible recovery of heavy metal ions from contaminated water with preferable performance, broadening sustainable development for purification systems.

Fast, reversible mechanochromism of regioisomeric oxazine mechanophores: Developing in situ responsive force probes for polymeric materials

Summary To address hysteretic or irreversible mechanochromism found in most bond-scission-based mechanophores, we developed a new family of mechanophores based on the oxazine (OX) structural motif. Three OX regioisomers differing in their point of attachment to the indole ring show variable mechanochromic mechanoresponsiveness in a polydimethylsiloxane (PDMS) matrix. Constrained DFT simulations correlate the experimental findings to molecular scale events; two of the three regioisomers exhibit a force-activated rearrangement, while the third one is mechanochemically inactive. Most significantly, when compared with the spiropyran (SP) and the naphthopyran (NP), the OX mechanophores exhibit faster and reversible mechanochromism without any sign of fatigue. Such a rapid response to mechanical loads is rationalized by the difference between SP and OX scaffolds, given that the SP ring opening is accompanied by a trans-cis isomerization step. These fast-responsive mechanophores are anticipated to bring deeper understanding to a broad range of soft materials by in situ monitoring the local mechanics.

Structurally photo-active metal–organic frameworks: Incorporation methods, response tuning, and potential applications

Metal–organic frameworks (MOFs) are an important family of materials due to the properties that make them well suited to a range of applications. This includes structurally photo-active MOFs, which have properties that can be efficiently modulated through controlled light irradiation, making them ideal due to the cost-effectiveness and noninvasive nature of this stimulus. The incorporation of structurally photo-active functional groups into MOFs has occurred through either guest inclusion, as pendant moieties, or as part of a ligand's backbone. While initial studies into the incorporation of these groups focused on prominent photo-switches such as azobenzenes, the literature has expanded to include other classes described in the wider photo-switch literature, most notably spiropyrans (SPs). The incorporation of alternative photo-switching classes has currently benefited the field through tuning the light responsive wavelength. Initial inquiries demonstrated suitable function in gas sorption applications where irradiation could be exploited for inducing adsorption or desorption. Furthermore, the potential applications explored in the literature have also recently expanded to include inquiries into other commercial functions, such as desalination [R. Ou et al., Nat. Sustain. 3, 1052–1058 (2020)], photo-lithography [H. A. Schwartz et al., Inorg. Chem. 56(21), 13100–13110 (2017)], and drug capture/release [X. Meng et al., Sci. Adv. 2(8), 2–8 (2016)].

Synthesis and photochromic behavior of comb-like acrylate polymer nanoparticle containing spiropyran

Spiropyran (SP) materials have attracted considerable interest owing to sensitive and efficient photochromic properties, but it is a challenge to obtain photochromic materials with excellent sensitive UV-responsivity and photodegradation resistance durability. In this study, a series of comb-like acrylate polymer nanoparticle latexes containing SP are fabricated via miniemulsion polymerization. The influence of the length of the alkyl side chain of comb-like acrylate polymer on some photochromic properties of SP is investigated. Compared with the short-side chain poly(butyl acrylate) (PBA) nanoparticles latexes, the comb-like acrylate polymer nanoparticle latexes with longer side chain possess better photoresponsivity and more excellent photodegradation resistance because the strong interaction and chain flexibility of comb-like alkyl side chain provide effective spaces for the SP→MC or MC→SP photochemical isomerization. The investigations of photochromic nanoparticle latexes guide an approach to reversible optical data storage, multipurpose photo-responsive sensing system and show promising application in the field of ultraviolet intensity indicator and flexible wearable UV protective clothing.

FRET processes of bi-fluorophoric sensor material containing tetraphenylethylene donor and optical-switchable merocyanine acceptor for lead ion (Pb2+) detection in semi-aqueous media

A novel aggregation-induced emission (AIE) structure containing a tetraphenylethene (TPE) unit covalently linked with a spiropyran (SP) unit was synthesized and investigated in semi-aqueous solutions with 90% water fraction. The open-form structure of red-emissive merocyanine (MC) unit combined with TPE unit was utilized as a bi-fluorophoric sensor to detect lead(II) ion, which could be transformed from the close-form structure of non-emissive SP unit upon UV exposure. Moreover, the TPE unit as an energy donor with the blue-green photoluminescence (PL) emission at 480 nm was combined with the MC unit as an energy acceptor with the red PL emission at 635 nm. Due to the Förster resonance energy transfer (FRET) processes, the bi-fluorophoric sensor produced more efficient ratiometric PL behavior to induce a stronger red PL emission than that of the mono-fluorophoric MC unit. Hence, the PL sensor responses of the AIE bi-fluorophoric structure toward lead(II) ion could be further amplified via the FRET-OFF processes to turn off red PL emission of the coordinated MC acceptor and to recover blue-green PL emission of the TPE donor. Accordingly, the best LOD value for the AIE sensor detection toward Pb2+ was 0.27 μM. The highest red MC emission with the optimum FRET process of AIE sensor could be utilized in cell viability tests to prove the non-toxic and remarkable bio-marker of AIE sensor to detect lead(II) ion in live cells. The developed FRET-OFF processes with ratiometric PL behavior of the bi-fluorophoric AIE sensor can be utilized for future chemo- and bio-sensor applications.

Magneto-responsive photochromic acrylic copolymer nanoparticles: An investigation into the mutual interactions and photoisomerization kinetics

Photoresponsive and magneto-responsive smart materials have received specific attention. Here, novel bifunctional polyacrylic nanoparticles were prepared via miniemulsion polymerization in which, magnetite nanoparticles (10–15 nm) were resided in the core and poly (methyl methacrylate-co-spiropyran ethyl acrylate) (poly (MMA-co-SPEA)) was located in the shell. Chemical bonding of spiropyran onto the surface of magnetite provided their close vicinity, leading to effective interactions which have not been studied before. The interactions between the excited state of merocyanine (MC) zwitterion from spiropyran (SP) group and magnetic field of the superparamagnetic Fe3O4 NPs were investigated. The results revealed the existence of mutual interactions and successful increment in the absorption intensity (up to 176%) and optical stability, 9% changes in the rate of photoisomerization and increment in the half life time of MC isomers. These were achieved in the presence of magnetite as well as enhancement in the magnetic properties by 10% under UV irradiation at 365 nm. Such synergistic and two-way interactions between magnetic field of the superparamagnetic Fe3O4 NPs and the produced instant dipole moments in MC may offer a new route toward preparation of dual responsive nanocomposite particles for light-triggered magnetic switches, magnetic-triggered photo switches and simultaneous sensing and separation probes.

Solid-State Reversible Dual Fluorescent Switches for Multimodality Optical Memory.

Fluorescent photoswitches are highly attractive, because they hold great promises for photonic devices and imaging. However, a limited number of reversible switches with a response to light have been achieved in the solid state. Here, we report reversible dual fluorescent photoswitching characteristics in the solid state of spiropyran (SP)-functionalized tetraphenylethene (TPE) derivatives. These photoswitches exhibit two distinct and selectively addressable states, a cyan fluorescence and a red fluorescence, which can be conveyed into each other in a reversible feature upon irradiation with alternating UV and visible light. Detailed spectroscopic and theoretical studies suggest that the nonplanar molecular conformation of TPE moieties leads to large free volumes, which facilitates the reversible photoisomerization of SP. The excellent reversibility and high-contrast fluorescence of solid-state photoswitches enable great applications in multimodality anticounterfeiting and optical writing and erasing fluorescent devices.

High-Performance Photochromic Hydrogels for Rewritable Information Record.

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

Re-usable colorimetric polymeric gel for visual and facile detection of multiple metal ions

For fast and visual detection of multiple metal ions, herein, a re-usable colorimetric polymeric gel with spiropyran moiety was fabricated. Under ultraviolet light, the spiropyran (SP) moiety could isomerize into the colored merocyanine (MC) isomer and chelate with divalent metal ion (M2+) and form MC-M2+ complexes. Chelated with different metal ions (Ca2+, Co2+, Zn2+, and Cu2+ions), the UV–Vis spectra of the gels could display the specific colorimetric response. When the metal-ions chelated gel was irradiated with Vis light, ions dissociated from MC and released from gel due to the MC moiety isomerized to the SP form. Furthermore, after 7 cycles of alternative UV–Vis irradiations, the gel showed excellent reversible chelation/dissociation of metal ion. The competitive tendency of metal ions to chelate with gel was as following: Cu2+ > Co2+ ≈ Zn2+ > Ca2+, which was in accordance with the density functional theory modeling. Using ionoprinting technology, the gel could achieve repeatability simultaneous detection of multiple metal ions. The light-triggered metal ion chelation/dissociation capability of the gel could be harnessed to construct reusable onsite platform for visual, fast, easy detection of multiple metal ions.

Molecular-Gated Drug Delivery Systems Using Light-Triggered Hydrophobic-to-Hydrophilic Switches.

A photoresponsive molecular-gated drug delivery system (DDS) based on silicone-hydrogel (poly(HEMA-co-PEGMEA)) interpenetrating polymer networks (IPNs) functionalized with carboxylated spiropyran (SPCOOH) was designed and demonstrated as an on-demand DDS. The triggered-release mechanism relies on controlling the wetting behavior of the surface by light, exploiting different hydrophobicities between the "closed" and "open" isomers of spiropyran as a photoswitchable molecular gate on the surface of IPN (SP-photogated IPN). Light-triggered release of doxycycline (DOX) as a model drug indicated that the spiropyran (SP) molecules provide a hydrophobic layer around the drug carrier and have a good gate-closing efficiency for IPNs with 20-30% hydrogel content. Upon UV light irradiation, SP converts into an open hydrophilic merocyanine state, which triggers the release of DOX. These results were compared with a previously developed SP-bulk modified IPN using the same hydrogel as a control, proving the efficiency of the gated IPN system. The covalent attachment of SPCOOH to the alcohol groups of the hydrogel and the structural change caused by UV light was indicated with FTIR analysis. XPS results also confirm the presence of SP by indicating the atomic percentage of nitrogen with respect to the hydrogel content.

On-Demand Reversible UV-Triggered Interpenetrating Polymer Network-Based Drug Delivery System Using the Spiropyran-Merocyanine Hydrophobicity Switch.

A reversible switchable on-demand UV-triggered drug delivery system (DDS) based on interpenetrating polymer networks (IPNs) with silicone as the host polymer and spiropyran (SP)-functionalized guest polymer is designed and demonstrated. The photo-responsive IPNs provide a new triggered drug delivery concept as they exploit the change in intermolecular interactions (work of adhesion) among the drug, matrix, and solvent when the incorporated hydrophobic SP moieties transform into the hydrophilic merocyanine form upon light irradiation without degradation and disruption of the DDS. The change in how the copolymer composition (hydrophilicity and content) and the lipophilicity of the drug (log P) affect the release profile was investigated. A thermodynamic model, based on Hansen solubility parameters, was developed to design and optimize the polymer composition of the IPNs to obtain the most efficient light-triggered drug release and suppression of the premature release. The developed IPNs showed excellent result for dopamine, l-dopa, and prednisone with around 90-95% light-triggered release. The model was applied to study the release behavior of drugs with different log P and to estimate if the light-induced hydrophobic-to-hydrophilic switch can overcome the work of adhesion between polymers and drugs and hence the desorption and release of the drugs. To the best of our knowledge, this is the first time that work of adhesion is used for this aim. Comparing the result obtained from the model and experiment shows that the model is useful for evaluating and estimating the release behavior of specific drugs merocyanine, IPN, DDS, and spiropyran.

Fast reversible isomerization of merocyanine as a tool to quantify stress history in elastomers.

A mechanochemistry based approach is proposed to detect and map stress history during dynamic processes. Spiropyran (SP), a force sensitive molecular probe, was incorporated as a crosslinker into multiple network elastomers (MNE). When these mechanochromic MNEs are loaded, SP undergoes a well-known force-activated reaction to merocyanine (MC) changing its absorption in the visible range (visible blue color). This SP to MC transition is not reversible within the time frame of the experiment and the color change reports the concentration of activated molecules. During subsequent loading–unloading cycles the MC undergoes a fast and reversible isomerization resulting in a slight shift of absorption spectrum and results in a second color change (blue to purple color corresponding to the loading–unloading cycles). Quantification of the color changes by using chromaticity shows that the exact color observed upon unloading is characteristic not only of the current stress (reported by the shift in color due to MC isomerization), but of the maximum stress that the material has seen during the loading cycle (reported by the shift in color due to the change in MC concentration). We show that these two color changes can be separated unambiguously and we use them to map the stress history in the loading and unloading process occurring as a crack opens up and propagates, breaking the material. Color maps on fractured samples are compared with finite element simulations and the agreement is excellent.