Spiropyran Molecules Research Articles

Effect of crystallization water on the magnetic properties of crystals composed of complexes of chromium(III) oxalate with spiropyran cations of indoline series

An increase in the effective magnetic moment and in the widths of the EPR lines of crystals composed of complexes of chromium(III) oxalates with cations of spiropyrans under the action of crystallization water was revealed. It was established that the dehydration-rehydration of the samples is a reversible process. Upon dehydration of the crystals at a temperature above 35°C, the triplet magnetism of the molecules of the spiropyrans weakens, strengthening upon rehydration. The contributions from the chromium oxalate and from the thermally induced states of the spiropyran molecules to the magnetization were isolated. The energies of thermal activation of the triplet states of the spiropyran molecules were determined.

Fabrication of Patterned Images in Photochromic Organic Microfibers

Photochromic spiropyran molecules were embedded in electrospun polymer microfibers. Electrospinning of a clear viscous chloroform solution containing a spiropyran and a matrix polymer, such as polystyrene and polyethylene oxide, affords polymer microfibers that are photoswitchable. Photomasked, 365 nm UV irradiation of the microfibers results in the generation of patterned color images owing to the selective transformation of the spiropyran molecules from their ring-closed SP to ring-opened MC form. The UV-irradiated areas display brilliant red fluorescence, which changes to green fluorescence upon prolonged irradiation.

Functionalization of single-walled carbon nanotubes with optically switchable spiropyrans

The design, synthesis and complete characterization of a smart material composed of single-walled nanotubes functionalized with spiropyran-based photo switchable molecules are reported. The chemical complexity of the system requires the use of a range of complementary techniques in order to provide a complete picture of the composition and performance of the nanomaterial. Thermal gravimetric analysis ensured both the high degree of chemical functionalization and the presence of molecular switches in the nanotube sample; micro-Raman indirectly confirmed the successful oxidation of the tubes, FT-IR proved the nature of the functional groups introduced based on their characteristic stretching vibrations and atomic force microscopy demonstrated nanotube lengths of approximately 600nm. UV–Vis–NIR absorption spectroscopy was used to evaluate the photoresponsive behaviour of the nanomaterial, and the intensity of the absorption band at 556nm could be modulated by light-induced reversible conversion of the spiropyran molecules attached to the SWCNT from the spiro close conformation to the merocyanine open form. We were also able to provide the first example of a continuous solution based on–off switching in a spiropyran–nanotube material.

Micro-environmental fine-tuning of electronic and kinetic properties of photochromic dyes

Despite the recognition of the importance of Spiropyran (SP)–Merocyanine (MC) photochromic materials in molecular switching, the majority of studies have been reported in solution with relatively few in the solid-state as required in modern displays and other devices. In contrast, the present work bridges solution, condensed phase and solid-phase media and is to our knowledge the first micro-environmental study on electronic and kinetic effects for the SP–MC system. Expanding on our previous work we have investigated the photochromic properties of an SP molecule (1b) attached to a 100 μm commercially available polystyrene micro-particle (Wang Resin). The thermal MC → SP reversion kinetics (5a,b → 4a,b and 2a,b → 1a,b) which reflect the critical lifetime of the open MC form were measured. Reduction in kobs of thermal reversion, MC → SP, up to two orders of magnitude, and a blue-shift up to 58 nm was observed with the potential for tailoring or fine tuning. The use of polymeric micro-particles in controlling both electronic and kinetic properties of photochromic molecular switches has been highlighted.

Stable and reversible optoelectrical dual-mode data storage based on a ferrocenlylspiropyran molecule

A spiropyran molecule bonded with ferrocene (SPFc) was synthesized as data storage medium. Optical recording pattern was obtained through the reversible modulation of UV and visible light on the SPFc film, which exhibited good reversibility compared with the spiropyran without ferrocene moiety. In addition, the SPFc thin film also possessed reversible electrical switching property with high ON/OFF ratio, low threshold voltage, and long retention time. Accordingly, reliable, stable, and reversible nanoscale data storage was achieved on the SPFc thin film by scanning tunneling microscopy. The results will be significant to develop multifunctional molecule and reversible multimode data storage.

Photostimulated electron transfer and its action on paramagnetism of Sp3Cr(C2O4)3 single crystals

The effect of irradiation by ultraviolet light on the effective magnetic moment of a paramagnetic single crystal based on photochrome spiropyran (Sp) and chromium oxalates Sp3Cr(C2O4)3 molecules is detected. It is shown that the deviation of the temperature dependence of the magnetic moment from the Curie law is caused not by the exchange interaction, but by electron redistribution between Cr3+ and Cr4+ ions and spiropyran molecules Sp0 and Sp+. Analysis of the angular dependence of EPR spectra makes it possible to determine the contribution of Cr3+ ions to the magnetic properties of the crystals and to determine the crystal field parameters D = 0.619 cm−1 and E = 0.024 cm−1. Irradiation of hydrated samples by ultraviolet light leads to intensity redistribution of EPR lines attributed to Cr3+ and Sp0. Thermally stimulated paramagnetism of triplet states of spiropyran ions Sp+ and the SpI salt is observed.

Spiropyran-based reversible, light-modulated sensing with reduced photofatigue

Switchable materials have tremendous potential for application in sensor development that could be applied to many fields. We are focusing on emerging area of wireless sensor networks due to the potential impact of this concept in society. Spiropyran-based sensors are probably the most studied type of photoswitchable sensing devices. They suffer from many issues but photofatigue, insufficient selectivity and lack of sensitivity are probably the most important characteristics that hinder their wider application. Here, we are address these issues and demonstrate that covalent attachment of modified spiropyran into a polymeric film significantly reduces photodegradation. The observed signal loss after 12th cycle of switching between the spiropyran and merocyanine forms is only about 27% compared to the loss of 57% of the initial signal in an equivalent experiment based on non-immobilized spiropyran. This has enabled us to demonstrate at least five reversible cycles of detection of an ion of interest (in our case H+) with minimal signal loss. Furthermore, we demonstrate that the sensitivity can be increased by incorporation of additional binding groups in the parent spiropyran molecule. Using molecular modelling to calculate the relevant bond lengths as a measure of interaction between MC and H+, the calculated increase of H-bond strength is approximately an order of magnitude for a derivative containing a methoxy group incorporated in the o-position of the parent spiropyran in comparison to the equivalent unsubstituted phenol. This theoretical result was found to correspond very well with experimental observation. As a result, we have increased the sensitivity to H+ by approximately one order of magnitude.

Conformation-Induced Electrostatic Gating of the Conduction of Spiropyran-Coated Organic Thin-Film Transistors

A facile method to make optoelectronic devices formed from organic thin-film transistors that are functionalized by photochromic spiropyran dyes in a nondestructive manner has been developed. When PDMS stamps are employed, alkane-containing spiropyran molecules can be coated simply onto the surface of organic thin films in a noninvasive manner. Upon UV irradiation, the molecules undergo isomerization from the neutral closed form to the charge-separated merocyanine form, producing the local electrostatic environment. This photoinduced electrostatic environment can function as a local negative gate voltage, thus increasing the electrical conductivity in p-type devices and decreasing the electrical conductivity in n-type devices. Further irradiation with visible light or keeping the devices in the dark can switch the device conductance back to their initial value. This method is reversible and reproducible on different devices with different thickness over a long period of time.

SIGNS OF STRESS

PEOPLE UNDER STRESS may exhibit certain telltale signs that indicate they’re near a breaking point. Some, for example, will turn bright red just before they blow their top. Now, a new polymer does the same thing, changing color when stressed to the point of mechanical failure ( Nature 2009, 459, 68). Such a material could be used as a damage sensor that enables researchers to assess the effects of stress on polymeric materials before they fail. The new polymers can change color thanks to the addition of spiropyran molecules that undergo electrocyclic ring-opening in response to mechanical force. The resulting ring-opened merocyanine molecules are brightly colored, producing red or purple hues in the polymer, depending upon how the indicator molecule is covalently linked to the polymeric structure. The spiropyran undergoes “a force-induced reaction inside of a solid structural polymer,” explains University of Illinois, Urbana- Champaign, materials science professor Nancy R. Sottos, who spearheaded the rese...

Linear and Hyperpolarizabilities of Spiropyran and Derivatives

The geometry of spiropyran molecule and its derivatives was found using quasi-Newton methods, BroydenFletcher{Goldfarb{Shanno technique. Then ab initio quantum chemical methods were applied to calculate the ground state energies of the closed and open forms of spiropyran for difierent basis sets. The frequency dependent linear polarizability of spiropyran and derivatives were obtained and plotted. The found absorption peaks are difierent for the closed and the open structures of the spiropyran molecule.

Kinetics of Photochromic Induced Energy Transfer between Manganese-Doped Zinc-Selenide Quantum Dots and Spiropyrans

Fluorescence resonance energy transfer (FRET) is investigated with manganese-doped ZnSe nanoparticles (quantum dots) as long fluorescence lifetime donors and spiropyran molecules as acceptors. The kinetics of photochemical ring-opening reaction of spiropyran upon UV-illumination is exploited to achieve efficient quenching of the manganese fluorescence lifetimes at a low temperature of 78 K in methylcyclohexane/isopentane mixture. Modulation of the acceptor structure from closed to open form allows us to investigate the temporal decrease in donor lifetime accompanied with an increase in the efficiency of FRET transfer. A theoretical model proposed by us describes very well the experimental data, thus providing the intimate parameters of FRET transfer in the system quantum dot−dye molecule.

Synthesis of high‐molecular‐weight linear methacrylate copolymers with spiropyran side groups: Conformational changes of single molecules in solution and on surfaces

AbstractP(BMA‐co‐HEMA‐spiropyran) was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization of butyl methacrylate (BMA) and 2‐(trimethylsilyloxy)‐ethyl methacrylate (HEMA‐TMS), removal of the TMS‐protective groups, and the polymer analogous esterification of the hydroxyethyl side chains with a spiropyran containing a carboxylic acid group. UV‐induced conformational changes of the synthesized macromolecules and low‐molecular‐weight spiropyran molecules were studied. Rate constants and half‐life times of the ring closure reaction from zwitterionic merocyanine to the spiropyran species were determined in the presence and absence of mica‐dispersed particles in toluene both with the free spiropyran and the polymer‐bound spiropyran. Scanning force microscopy was used to visualize the conformation of spiropyran‐decorated single macromolecular chains and agglomerated polymer‐bound merocyanine adsorbed on mica. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1274–1283, 2009

Mesostructured self-assembled silica films with reversible thermo-photochromic properties

A spiropyran molecule has been introduced via one-pot synthesis into mesostructured silica films, which have been obtained through a micelle templating self-assembling process. The mesostructure has been characterized by transmission electron microscopy and small-angle X-ray scattering performed with synchrotron light. The final material exhibited a p6mm 2d-hexagonal organization and the mesostructure has not been affected by the introduction of spiropyrans in the precursor solution. A comparative characterization of the optical properties of the spiropyrans dissolved in different solvents and after incorporation in the mesostructured films has been done by UV–Vis absorption spectroscopy, fluorescence spectroscopy and ellipsometric spectroscopy. The spiropyran-doped films appeared transparent before external stimuli had applied, a colour change to yellow (thermally induced) or to red (light induced) has been observed. Both the colour changes have been observed to be reversible under room temperature or visible light exposure; the colour transitions have been attributed to different equilibria among the various forms of merocyanine of spiropyrans.

Synthesis and photochromic property of nanoparticles with spiropyran moieties via one-step miniemulsion polymerization

Photochromic nanoparticles with spiropyran moieties were prepared by a facile one-step miniemulsion polymerization. The nanoparticle dispersion was obtained by mixing the monomers, spiropyran-containing molecules and hydrophobe, dispersing them into an aqueous solution with surfactant, subjecting the dispersion to ultrasonification and polymerizing the monomers by using a water soluble initiator. The shape and size of the nanoparticles was determined with the atomic force microscope (AFM) and dynamic light scattering (DLS), and the determined average diameter of the nanoparticles ranges from 30 nm to 60 nm. The absorption and fluorescence spectra for the nanoparticles dispersions reveal that the spiropyran molecules were successfully incorporated in the polymer nanoparticles. Moreover, the nanoparticle dispersions were found to exhibit enhanced photo-reversibility, photo-stability and relatively fast photo-responsive property compare to the same species in aqueous solution.

Reversibly Photo-Responsive Polymer Surfaces for Controlled Wettability

Photochromic spiropyran molecules are utilized as additives for the development of polymer surfaces whose wetting characteristics can reversibly respond to irradiation with laser beams of properly chosen photon energy. The hydrophilicity is enhanced upon UV laser irradiation due to the photo-induced isomerization of the non-polar spiropyran molecules to the polar merocyanine. The situation is reversed upon green laser irradiation. Micropatterning of the photochromic-polymer films using soft lithography or photo-polymerization techniques affects their wettability towards a more hydrophobic or more hydrophilic behavior depending on the dimensions of the patterned features and on the hydrophilicity/hydrophobicity of the flat surface. The light-induced wettability variations of the structured surfaces are enhanced by up to a factor of three as compared to those on the flat surfaces. This enhancement is attributed to the photo-induced reversible volume changes to the imprinted gratings, which additionally contribute to the wettability changes due to the light-induced photochromic interconversions.

Formation of Metal-free J-aggregates in Merocyanine/Spiropyran Mixed Langmuir-Blodgett Film

In order to fabricate metal-free J-aggregate, merocyanine(MD)/spiropyran(SP) mixed LB film was transferred on a glass plate from a pure aqueous solution. Upon UV-light illumination, SP molecules isomerized from SP-form to photomerocyanine (PMC)-form and PMC-form molecules formed J-aggregate with self-assembly. Subsequent vapor-treatment of dimethylamine (DMA) aqueous solution after UV-light illumination induced J-aggregate formation of MD molecules. Metal-free J-aggregate of MD dye was formed by the stepwise treatment of UV illumination and the DMA vapor treatment. The formation mechanism of J-aggregate was discussed.

Photo-, Thermally, and pH-Responsive Microgels

Microgels with photo-, thermally, and pH-responsive properties in aqueous suspension have been synthesized and characterized using dynamic light scattering and UV-visible spectroscopy. The new route involved first preparing poly(N-isopropylacrylamide) (PNIPAM)-allylamine copolymer microgels and a spiropyran photochrome (SP) bearing a carboxylic acid group. Then the functionalized spiropyran was coupled to the microgel via an amide bond. The dark-equilibrated gel particles feature spiropyran molecules in the polar, merocyanine form. After irradiation of visible light, the particle size becomes smaller because spiropyran changes to the relatively nonpolar, closed spiro form. The PNIPAM-SP microgels undergo a volume phase transition in water from a swollen state to a collapsed state with increasing temperature under all light conditions. However, the transition temperature range of the PNIPAM-SP is much broader than that for the PNIPAM without SP. The PNIPAM-SP microgels are monodisperse and self-assemble into a crystalline lattice while in suspension. The UV-visible spectra of an aqueous suspension of PNIPAM-SP microgel in the dark-adapted, merocyanine form showed both an absorption peak around 512 nm due to the merocyanine (giving a reddish color to the suspension) and two sharp peaks from Bragg diffraction of colloidal crystallites. Upon visible irradiation, the 512-nm band bleached significantly due to spiropyran photoisomerization. The spiropyran photoisomerization and accompanying color changes of the suspension were reversible upon alternating dark, UV, and visible light irradiation. Due to the residues of amine groups, the swelling capability of PNIPAM-SP microgels reduces as the pH value is changed from 7 to 10.

Smart photochromic gratings with switchable wettability realized by green-light interferometry

We demonstrate the enhancement of the wetting properties of smart photochromic surfaces by a specifically developed, gentle interferometric patterning employing green light. We realized photochromic gratings with 2.5–10.0μm period by a blend consisting of a green-curable matrix and spiropyran molecules. The structured surfaces exhibit photocontrolled and reversible wettability, and enhanced hydrophilicity with respect to the native substrates. The dynamics of liquid spreading onto the gratings was also investigated, and the wetting behavior analyzed according to Wenzel’s [Ind. Eng. Chem. 28, 988 (1936)] model for rough surfaces. These results indicate switchable gratings as promising functional components for microfluidics and modulation, and green-light interferometry as a reliable lithographic method for patterning organics without degradation or photochemical reactions.

Control of Nanopore Wetting by a Photochromic Spiropyran: A Light-Controlled Valve and Electrical Switch

By modifying the surface of nanoporous alumina membranes using mixtures of a photochromic spiropyran and hydrophobic molecules, it is possible to control the admission of water into the membrane using light. When the spiropyran is in the thermally stable, relatively hydrophobic closed form, the membrane is not wet by an aqueous solution. Upon exposure to UV light, the spiropyran photoisomerizes to the more polar merocyanine form, allowing water to enter the pores and cross the membrane. Thus, the photosensitive membrane acts as a burst valve, allowing the transport of water and ions across the membrane. If the aqueous solution contains ions, then the membrane acts as an electrical switch; photoisomerization leads to a two-order-of-magnitude increase in ionic conductance, allowing a current to flow across the membrane. Exposure to visible light causes photoisomerization of the merocyanine back to the closed, spiro form, but dewetting of the membrane does not occur spontaneously, due to a high activation barrier.

Combination of microstructuring and laser-light irradiation for the reversible wettability of photosensitised polymer surfaces

The wetting characteristics of surfaces of polymers doped with photochromic spiropyran molecules can be tuned when irradiated with laser beams of properly chosen photon energy. In particular, UV laser pulses at 308 nm are responsible for the enhancement of the hydrophilicity of the surfaces, since the embedded non-polar spiropyran molecules convert to their polar merocyanine isomers upon UV absorption. The process is reversed upon irradiation with green laser pulses at 532 nm. When the photochromic-polymeric surfaces are micropatterned using soft lithography or photo-polymerisation techniques, they can change their wettability towards a more hydrophobic or more hydrophilic behaviour depending on the dimensions of the patterned features and on the hydrophilicity-hydrophobicity of the flat surface. Furthermore, the light-induced wettability variations on these structured surfaces are greatly enhanced compared to the flat surfaces. This significant increase to the wettability changes is attributed to the combination of the photochromic interconversions upon laser irradiation together with the photoinduced reversible volume changes of the patterned features.