Isomerization Of Spiropyran Research Articles

Atomic Charge Dependency of Spiropyran/Merocyanine Adsorption as a Precursor to Surface Isomerization Reactions.

This computational study investigates the adsorption of various spiropyran and merocyanine isomers on a NaCl substrate using a combination of density functional theory (DFT) and molecular mechanics (MM) calculations. Four different charge methods were used to determine the partial atomic charges for the adsorbate molecules, including Mulliken population analysis and three electrostatic potential (ESP) methods (Merz-Kollman, ChelpG, and Hu-Lu-Yang), while three different force fields (AMBER 3, CHARMM 27, and MM+) were employed for the MM calculations. The results show that the various DFT charge methods produced similar outcomes for the molecules' partial atomic charges, with some exceptions for individual atoms and methods. Additionally, it was found that the ESP charge methods were more sensitive to the conformer orientation than the Mulliken approach. The adsorption behavior of merocyanine conformers with the central bond in trans orientation (T-conformers) was similar for various configurations, with the molecule adsorbing mostly flat with its aromatic rings almost parallel to the substrate. However, C-conformers (with their central bond in cis orientation) and spiropyran isomers exhibited inconsistent adsorption behavior, mostly because only some of the aromatic rings contributed to the adsorption behavior. Due to additional van der Waals interactions of more aromatic rings, the adsorption energies for T-conformers are consistently 0.2-0.3 eV higher than for C-conformers and for spiropyran. The study found that the adsorption geometries and energies of stable T-conformers were independent of the partial atomic charge scheme and force field used, and C-conformers show parameter-dependent behavior upon adsorption, leading to metastable configurations. These findings indicate viable pathways during the spiropyran-merocyanine isomerization reactions. Therefore, the results provide initial insights into the possibility of switching spiropyran isomers into merocyanine isomers and vice versa after adsorption onto substrates.

Multi-responsive chromatic hydrogel exhibiting reversible shape deformations

In this work, deformable and chromatic hydrogel triggered by multi-stimuli was fabricated. This hydrogel was composed of N-isopropylacrylamide (NIPAAm), acryl-6-aminocaproic acid (A6ACA), and spiropyran (SP) derivatives, which possessed ferric ion (Fe3+) and temperature-triggered shape deformations properties as well as chromatic behavior. Under ultraviolet light irradiation, the SP isomer in the hydrogel transformed to the merocyanine (MC) isomer, and the hydrogel showed the characteristic UV–Vis absorption peak of MC at 540 nm. The hydrogel revealed the selective chromatic response to Fe3+ with the disappearance of the absorption peak of MC. Using ionoprinting technology, the hydrogel deformed programmatically in the presence of Fe3+. Moreover, owing to the anisotropic structure of the chromatic hydrogel, it realized reversible bending deformation triggered by temperature. The behaviors of hydrogels in response to dual stimuli (Fe3+ and temperature) were further investigated, and the hydrogel showed programmable, spatiotemporal, and complex deformation behaviors, accompanying by the color change. This hydrogel will have great application potential in soft robotics, soft actuators, and environmental sensors.

Well-controlled spiropyran functionalized polystyrenes via a combination of anionic polymerization and hydrosilylation for photoinduced solvatochromism

Si–H-functionalized polystyrene (PS–SiH) with a well-controlled molecular weight and narrow polydispersity index (PDI) was synthesized via anionic polymerization (AP) of (4-vinylphenyl)-dimethyl-silane (VPDMS), i.e., PVPDMS (Mn = 2.5 kg/mol, PDI = 1.16). Spiropyran (SP) derivatives as the photo-responsive function, i.e., SP-phenyl-Yne (M1) and SP-biphenyl-Yne (M2) bearing the same alkyne (Yne) terminals and different spacers (phenyl/biphenyl), were used to modify the resulting PVPDMS via hydrosilylation, affording SP-functionalized PSs (PVPDMS-SPM1/SPM2) with a defined number of SP attachments. The photoinduced solvatochromism of SP derivative small molecules and polymers was investigated in solvents of different polarities. The time-dependent conversion of different isomers was mainly qualitatively tracked by spectroscopic methods, allowing the transfer pathways among different SP isomers to be proposed. The appearance of trans-merocyanine (MC) H-aggregations was detected in the UV–Vis spectra of both SP derivative small monomers and polymers in relatively low-polarity solvents. Moreover, a discoloration process caused by the appearance of cis-MCs was observed under continuous illumination, which demonstrated that the appearance of aggregations and cis-MCs relied on the solvent polarity. More importantly, PVPDMS as the polymer backbone effectively decreased the rate of structural trans-to-cis MC conversion, indicating an inhibiting effect of the steric hindrance on the appearance of cis-MC molecules.

Photo-/Baso-Chromisms and the Application of a Dual-Addressable Molecular Switch.

Two typical molecular switches of spiropyran (SP) and benzoxazine (OX) were fused by sharing an indole to achieve a new dual-addressable molecular switch (SP-OX-NO2 ). Through proper molecular modification with NO2 , the transformation from merocyanine (MC) to ring-closed SP or ring-closed OX can be controlled separately with visible light or base stimuli in solution, respectively, and these processes are verified by UV-vis and NMR spectroscopy as well as control experiments. The cis-merocyanine (cis-MC) form is involved in the basochromic process in solution. DFT calculation suggests that the bidirectional switching property of the fused SP-OX molecular switch can be controlled separately, when the OX isomer is more stable than the deprotonated SP isomer. Because of the significant color variations in solution, the simple dual-addressable switch has been further successfully applied to construct a multicolor reversible display on paper.

Light-Responsive Size of Self-Assembled Spiropyran-Lysozyme Nanoparticles with Enzymatic Function.

Novel light-responsive nanoassemblies with switchable size and enzymatic activity are built from a protein and a water-soluble spiropyran. Assemblies are created by electrostatic self-assembly in aqueous solution such that the photochromic property of the spiropyran enables light responsiveness. Upon visible light exposure, the aggregate size increases from 200 to 400 nm. The enzyme retains its activity upon aggregation into the assembly, while it decreases through visible light irradiation. Fundamentally, we show how the two different spiropyran isomers, the open-ring merocyanine form and the closed-ring spiropyran form, bind differently to the protein, which triggers the assembly size and use of thermodynamic data to understand the binding process and the size response. Thus, as a proof of concept, a self-assembly driven light-tunable enzyme activity in conjunction with a triggerable assembly size is demonstrated for a model system. The concept bears future potential for various possible biological applications ranging from genetic control over vaccine applications to the detection of certain proteins.

Mechanical Reactivity of Two Different Spiropyran Mechanophores in Polydimethylsiloxane

We investigate the effect of pulling point location on the mechanochemical activation of two isomers of spiropyran in cross-linked polymeric materials through computational calculations and in situ fluorescence measurements. The threshold stress and strain required to activate the spiropyran mechanophores under tensile load are characterized. For both spiropyran isomers, applied stress favors the activated merocyanine states; however, despite differences in mechanochemical behavior predicted by quantum chemical calculations and previous single molecule experiments, both spiropyran isomers exhibit similar mechanochemical reactivity in bulk polymeric materials. The kinetics of the spiropyran–merocyanine transition under different tensile stresses are also examined. Overall, we find that varying the pulling geometry on the spiropyran mechanophore has only a minimal effect on the mechanical activation in bulk polymeric materials due to the complex nature of the macroscopic system.

Photo-control of the mitotic kinesin Eg5 using a novel photochromic inhibitor composed of a spiropyran derivative.

In this study, we synthesized a novel photochromic inhibitor of the mitotic kinesin Eg5, which is composed of the photochromic compound spiropyran to photo-control the function of Eg5. The compound (S)-2, 3-dispiropyran propionic acid (DSPPA) exhibits reversible spiropyran-merocyanine photo-isomerization upon irradiation with visible or ultra-violet light. DSPPA induced reversible changes in the inhibitory effect on Eg5 ATPase and motor activities, which correlates with the spiropyran-merocyanine photo-isomerization. Microtubule-dependent ATPase activity was significantly more inhibited by the spiropyran isomer of DSPPA than by the merocyanine isomer. Additionally, an in vitro motility assay revealed that the microtubule gliding velocity was reduced more by the spiropyran isomer than by the merocyanine isomer. This indicates that the spiropyran derivative may be useful in regulating the function of the mitotic kinesin.

Adsorption and switching properties of nitrospiropyran on Bi(1 1 4)

Spiropyrans are prototype molecular switches, which undergo a reversible photoinduced ring-opening/-closure reaction between the closed three-dimensional spiropyran (SP) and the open, planar merocyanine (MC) form. In solution the SP isomer is the thermodynamically stable form. Using high resolution electron energy loss spectroscopy, we resolve a thermally-activated irreversible ring-opening reaction of nitrospiropyran resulting in the MC form for coverages above one monolayer. Thus, the situation found in solution is reversed for the adsorbed molecules, since the MC form is more stable due to the modified energetics by the presence of the substrate. In addition, illumination with blue light (445 nm) induced also the ring-opening, while the photostimulated back-reaction could not be observed. The photoisomerization is driven by a substrate-mediated process, i.e. a charge transfer from the substrate into molecular states. The situation changes completely in the monolayer regime. Neither a thermally-assisted nor a photoinduced ring-opening reaction has been identified. We ascribe the suppression to sterical effects stabilizing the SP form due to the surface structure of Bi(1 1 4), which consists of straight atomic rows separated by rough valleys.

Blue to near-IR energy transfer cascade within a dye-doped polymer matrix, mediated by a photochromic molecular switch.

The spectroscopic properties of a poly(methyl methacrylate) matrix doped with a coumarin dye, a cyanine dye, and a photochromic spiropyran dye have been investigated. Before UV irradiation of the matrix, excitation of the coumarin dye results in minimal energy transfer to the cyanine dye. The energy transfer is substantially enhanced following UV irradiation of the matrix, which converts the colourless spiropyran isomer to the coloured merocyanine isomer, which then acts as an intermediate bridge by accepting energy from the coumarin dye and then donating energy to the cyanine dye. This demonstration of a switchable energy transfer cascade should help initiate new research directions in molecular photonics.

Preparation of a conjugation-ready thiol responsive molecular switch

In this work we synthesize molecular switches that are responsive to cysteine, homocysteine, and glutathione; three redox systems that make up the majority of the body’s antioxidant defenses. Synthesized spiropyran isomers with conjugation-ready linkages showed good selectivity of response to these major antioxidant thiols over nucleophilic amino acids; however the position of the linking group can affect selectivity and reversibility of the switching response. An isomer with selectivity for cysteine against GSH and Hcy was identified.

Photoregulation of α-Chymotrypsin Activity by Spiropyran-Based Inhibitors in Solution and Attached to an Optical Fiber.

Here the synthesis and characterization of a new class of spiropyran-based protease inhibitor is reported that can be reversibly photoswitched between an active spiropyran (SP) isomer and a less active merocyanine (MC) isomer upon irradiation with UV and visible light, respectively, both in solution and on a surface of a microstructured optical fiber (MOF). The most potent inhibitor in the series (SP-3 b) has a C-terminal phenylalanyl-based α-ketoester group and inhibits α-chymotrypsin with a Ki of 115 nM. An analogue containing a C-terminal Weinreb amide (SP-2 d) demonstrated excellent stability and photoswitching in solution and was attached to the surface of a MOF. The SP isomer of Weinreb amide 2 d is a competitive reversible inhibitor in solution and also on fiber, while the corresponding MC isomer was significantly less active in both media. The ability of this new class of spiropyran-based protease inhibitor to modulate enzyme activity on a MOF paves the way for sensing applications.

Force-rate characterization of two spiropyran-based molecular force probes.

The mechanically accelerated ring-opening reaction of spiropyran to a colored merocyanine provides a useful method by which to image the molecular scale stress/strain distribution within a polymer, but the magnitude of the forces necessary for activation has yet to be quantified. Here, we report single molecule force spectroscopy studies of two spiropyran isomers. Ring opening on the time scale of tens of milliseconds is found to require forces of ∼240 pN, well below that of previously characterized covalent mechanophores. The lower threshold force is a combination of a low force-free activation energy and the fact that the change in rate with force (activation length) of each isomer is greater than that inferred in other systems. Finally, regiochemical effects on mechanochemical coupling are characterized, and increasing force reverses the relative ring opening rates of the two isomers.

Optical switching of carrier transport in polymeric transistors with photochromic spiropyran molecules

We demonstrate the optical switching of transistor properties by adopting the photoisomerization of spiropyran (SP) molecules dispersed in a poly(triarylamine) (PTAA) channel layer. The drain current (IDS) was reduced by ultra-violet (UV) light irradiation, while visible (VIS) light irradiation restored the IDS to its original value. The UV and VIS light irradiation brought about the photoisomerization reactions of SP, i.e., an ionic polarized open-ring isomer was induced by UV and a less polarized closed-ring isomer was induced by VIS. To clarify the mechanism of the photoisomerization-induced optical switching, we evaluated the variations in transistor properties, namely IDS, carrier mobility and threshold voltage, when subjected to UV and VIS light irradiation. We found that the ionic polarized open-ring SP isomer worked as a carrier scattering site that effectively suppressed carrier transport in the polymer channel.

Stabilization of merocyanine by protonation, charge, and external electric fields and effects on the isomerization of spiropyran: a computational study

Protonation, charging, and field effects on the thermal isomerization of a nitrospiropyran (SP) modified by a thiolated etheroxide chain into merocyanine (MC) are computationally studied at the DFT level. The ring opening leads to cis-MC conformers that then isomerize to the more stable trans forms. While the closed neutral spiropyran is more stable than the conjugated open forms, the merocyanine conformers are significantly stabilized by protonation, electron attachment, and ionization. For protonation on the pyran oxygen atom and electron attachment, the MC conformers are more stable than SP, and unlike for the neutral species, the ring opening is spontaneous at room temperature. Moreover, for the pyran oxygen-protonated form, the ring opening to the cis-merocyanine becomes barrierless. On the other hand, barriers comparable to the neutral remain along the thermal pathway to the cis-merocyanine conformer for ionization or electron attachment, and the barrier for isomerization is significantly higher for the N-protonated SP form. External field effects on the neutral reaction path show that ring opening to the cis-merocyanine is favored when the field reduces the electron density on the pyran part, as also induced by the local field due to O protonation.

Selective Acceleration of the Protonated Merocyanine‐Spiropyran Photochromic Transformation by Inclusion in Cucurbit[7]uril

The effect of cucurbit[7]uril (CB7) on the spiropyran-merocyanine photochromic interconversion was studied in acidic and alkaline aqueous solutions. The merocyanine (MC) isomer was found to be the thermodynamically most stable form both in water and in the presence of CB7. A preferential binding of the protonated merocyanine (MCH(+)) to CB7 was observed with an equilibrium constant of 7.4×10(4) m(-1), and the complex formation led to significant diminution of acidity of the guest. The photoinduced transformation of MCH(+) to the spiropyran isomer was accelerated 2.3-fold upon addition of CB7, whereas the rates of the other photochromic processes were not affected. The partial inclusion of MCH(+) in CB7 led to dual fluorescence due to the incomplete deprotonation in the singlet-excited state.

ChemInform Abstract: Syntheses, Cation Complexation, Isomerization and Photochemical Cation- Binding Control of Spirobenzopyrans Carrying a Monoazacrown Moiety at the 8-Position.

Spirobenzopyran derivatives carrying a monoazacrown moiety, such as 12-crown-4, 15-crown-5, and 18-crown-6 moieties, and their acyclic analogue, at the 8-position have been synthesized. Alkali metal ion complexation by the crowned spirobenzopyrans, followed by isomerization to the corresponding merocyanine form, and their photoisomerization, have been studied by cation extraction, absorption spectroscopy, and NMR spectroscopy. Binding of alkali metal ions (Li+, Na+ and K+) by the crown moieties leads to isomerization of the crowned spirobenzopyrans even under dark conditions. 7Li and 23Na NMR spectroscopy suggest that in the merocyanine isomer complexing an alkali metal ion, especially Li+, the crown-complexed metal ion interacts intramolecularly with the phenolate anion, thus being bound more powerfully than that in the corresponding spiropyran isomer, owing to anion, thus being bound more powerfully than that in the corresponding spiropyran isomer, owing to an additional-binding-site effect. UV-light irradiation in tetrahydrofuran further promotes the isomerization to the merocyanine form, the thermal stability of which depends significantly not only on the ion selectivities of their crown moieties but also on the ease of the intramolecular interaction between the crown-complexed metal ion and the phenolate anion. Under visible-light irradiation, the cation-bound merocyanine form readily reverts to the spiropyran form, releasing the metal ions to some extent. Alternating irradiation with UV and visible light or turning-on and -off of visible light, therefore, causes the isomerization of crowned spirobenzopyrans even in the presence of alkali metal ions, in turn affording control of their cation-complexing abilities.

Modulation of T2 Relaxation Time by Light-Induced, Reversible Aggregation of Magnetic Nanoparticles

A reversible T2 contrast agent consisting of cross-linked anionic dextran coated iron oxide nanoparticles covalently coupled to a light-sensitive spiropyran (SP)/merocyanine (MC) motif was synthesized and characterized. In aqueous solution, light induced isomerization of the molecular switches between the hydrophobic SP isomer and hydrophilic MC isomer directs the aggregation and dispersion of the nanoparticles, respectively. When in the dark, where the MC form dominates, the probe has a T2 relaxation time of 37.09 ms (60 MHz, 37 degrees C) and two size populations at 70 and 540 nm. After irradiation with visible light, the T2 relaxation time is shortened 33.7%, and the size correspondingly shifts to a single population at 520 nm upon aggregation. This "smart" T2 agent provides the advantage of reversibility which may enable dynamic monitoring with MRI. In addition, the light responsiveness of this agent suggests the potential to employ them as MRI gene reporters for the luciferase expression system.

Spiropyran-Merocyanine Equilibrium in Presence of Organic Acids and Bases

ABSTRACT Manipulation of the rate of thermal reversion of N-functionalized merocyanines (MC) to the corresponding spiropyran isomers in the dark, was demonstrated by using both organic acid and base additives. In the presence of organic bases, increase or decrease of the rate of reaction was dependent on the solvent used. When organic acids were used, in all cases the reaction rate decreased when compared with the system containing no acid. Similar behavior was also observed in polymer films. This approach is of interest for applications in the design of optical switches and memory with enhanced stability of the stored information.

Complexation of phenols with β‐ and γ‐cyclodextrins: determination of the association constants by using the isomerization of spiropyran

Complexation of phenols with β‐ and γ‐cyclodextrins: determination of the association constants by using the isomerization of spiropyran

Complexation of phenols with β‐ and γ‐cyclodextrins: determination of the association constants by using the isomerization of spiropyran

Complexation of phenols with β‐ and γ‐cyclodextrins: determination of the association constants by using the isomerization of spiropyran