Synthesis and characterization of coumarin-based spiropyran photochromic colorants

Two coumarin-based spiropyran derivatives were synthesized and characterized in two steps to explore their photochromic properties. Both prepared compounds are sensitive to UV light and change colors upon irradiation. The resulting photogenerated zwitterions revert to the original compounds while being heated. A new family of organic photochromic colorants is introduced.     

Photo‐switchable spiropyran immobilized polystyrene beads using catechol chemistry

Catechol and spiropyran functional groups were conjugated to a polymer backbone, allowing immobilization on polystyrene beads (PS beads). The final product was capable of stably reproducing the optical properties of spiropyran. Through the outstanding surface adhesion properties of the catechol functional group, spiropyran was immobilized on PS beads. Switchable photoluminescence in the spiropyran coated PS bead surfaces was observed depending on irradiation with either UV or visible light. The surfaces of the PS beads were morphologically examined by field emission scanning electron microscopy and X‐ray photoelectron spectroscopy was used for characterization of the constituent atoms. Furthermore, UV–Vis and fluorescence spectroscopy were used to confirm conversion between the spiropyran (SP) and merocyanine (MC) forms through UV or visible light irradiation on SP, while fluorescent images for both SP and MC were studied using confocal laser scanning microscopy. The confocal images of the SP‐PS beads system onto MDAMB‐231 cells under UV and visible light indicate the cellular uptake by emerging color within the cytoplasm. Advancing study, the remaining catechol groups can confers adhesive properties, given by contact angle data of various coated surfaces film. These stimuli‐responsive coatings are compatible as drawing switchable photochromic material on versatile substrate shown in confocal images of propylene film. Overall, this great water solubility and biocompatibility PS beads system also showed potential as cell bio‐imaging light stimuli responsive material, and the benefits of this system can also possibly address coat able advanced material for a wide range of surface light sensor applications. Copyright © 2017 John Wiley & Sons, Ltd.     

Formation of photochromic spiropyran polymer brushes via surface-initiated, ring-opening metathesis polymerization: reversible photocontrol of wetting behavior and solvent dependent morphology changes

In this article, we described a method for the formation of photochromic polymer brushes grafted from oxide surfaces using surface-initiated ring-opening metathesis polymerization of spiropyran-based monomers in the presence of second generation Grubbs catalyst. The growth of the polymer film, as monitored by ellipsometry and atomic force microscopy (AFM), is strongly influenced by the initial concentrations of the catalyst and monomer, as well as reaction time. These densely packed and highly smooth polymer films were successfully used as surfaces with switchable color and wettability using light as the external stimulus. The relatively nonpolar spiropyran can be switched to a polar, zwitterionic merocyanine isomer (with a larger dipole moment) using light of the appropriate wavelength. This process is reversible and can be switched back using visible light. The spiropyran-merocyanine photoinduced isomerization gives a reversible contact angle change up to 15 degrees for smooth Si/SiO 2 substrate under sequential irradiation cycles with UV and visible light. This contact angle change can be amplified by complexing the merocyanine form with metal ions through the phenolate oxygen, which enhances the switching of wettability with these polymer brushes. Irradiation in the presence of cobalt(II) ions gives rise to a contact angle variation as high as 35 degrees . This is the largest change in photoinduced surface wettability observed for a flat substrate. Photoisomerization in spiropyrans also yields a change in the refractive index of the film, which we have investigated using ellipsometric imaging. Lastly, morphological changes accompanying photochromism were investigated using atomic force microscopy. Significant morphological changes can only be induced in the films by irradiating in polar solvents that help to stabilize the merocyanine ring open form.     

Light-induced modulation of self-assembly on spiropyran-capped gold nanoparticles: a potential system for the controlled release of amino acid derivatives

A photoswitchable double-shell structure on Au nanoparticles, consisting of photochromic spiropyran as the first shell, which regulates the assembly and release of an outer shell of amino acid derivatives upon irradiation, is being reported for the first time. The light-regulated changes in the topographic properties of spiropyran-capped Au nanoparticles (i.e., interconversion between the zwitterionic and neutral forms) are exploited for the assembly and release of amino acid-based therapeutic agents such as l-DOPA.     

Preparation and properties of photochromic bacterial cellulose nanofibrous membranes

The photochromic bacterial cellulose (BC) nanofibrous membranes containing 1′,3′,3′-trimethyl-6-nitrospiro(2H-1-benzopyran-2,2′-indoline) (NO₂SP) were successfully prepared by surface modification of BC nanofibers with spiropyran photochromes, and their physical and photochromic properties were characterized. The FTIR spectra indicated the interaction between BC and NO₂SP which leads to the uniform dispersion of NO₂SP in the nanofibrous membrane. SEM results demonstrated that the introduction of NO₂SP maintains the nanofibrous network structure of BC. UV/vis spectrometry of the resulting BC-NO₂SP revealed that the membranes show reversible photochromic property by changing their color from colorless to pink forming a merocyanine structure upon UV irradiation, and returning back again to colorless spiropyran structure by visible light. The contact angle of the BC-NO₂SP with water was found to be reversibly regulated due to the reversible isomerization of the spiropyran moieties in BC-NO₂SP. The result indicates that the surface modification with spiropyran photochromes expands new applications of BC nanofibers and such photochromic nanofibers with excellent photosensitivity have great potentials for sensitive displays, biosensors and other optical devices.     

Preparation and photochromic properties of oligomeric poly(dimethylsiloxane) with the spiropyran or spirooxazine moiety in the side chain

Spirobenzopyran 1 , with the 3-(diethoxymethylsilyl)-propyl group at the N atom, was synthesized. The condensation reaction of the spiropyran 1 and diethoxydimethylsilane gave oligomeric poly(dimethylsiloxane) with the spiropyran moiety in the side chain. The oligomer was photochromic; its colour changed from colorless to purple-red on uv irradiation and the color faded on visible irradiation or on standing in the dark. The half-decay time of the thermal decoloration was about twice that of monomeric spiropyran dissolved in the dimethylsiloxane oligomer. Photochromic poly(dimethylsiloxane) with the spirooxazine moiety in the side chain was also prepared.     

Photoresponsive n-channel organic field-effect transistors based on a tri-component active layer

Photoresponsive OFETs were fabricated based on a tri-component active layer (NDI2OD-DTYM2, spiropyran and polystyrene). The results demonstrated that these OFETs displayed photoresponsive feature to alternate UV and vis light due to the photoisomerization of spiropyran between the closed-ring state and ionic open-ring state.     

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.     

Synthesis of novel chalcone derivatives and their stabilization effect of spiropyran in PMMA films

Three novel bis-chalcone derivatives with different alkyldioxy spacers were synthesized and dispersed into polymethyl methacrylate(PMMA) chloroform solution with 6-nitro-1’-ethyl-3’,3’-dimethylspiro-2H-1-benzopyran-2,2’-indoline(ESP) to prepare photochromic PMMA films in a facile way.After irradiation with 365 nm UV light,the photocrosslinking reaction between chalcone units was proved to retard the dccolorization of merocyanine form of the photochromic spiropyran effectively,as results of the steric hindrance produced by photocycloaddition of chalcone groups.It has been found that the bis-chalcone molecule with the shortest spacer has the most effective stabilizing effect on retardation of decoloration of spiropyran.     

Photochromic Doped Sol-Gel Materials for Fiber-Optic Devices

Photochromic-doped sol-gel materials have been prepared by adding a spiropyran photochromic dye to a solution of ethoxy silane monomers containing non-reacting ethyl radicals. After polymerization, normal photochromism (i.e., colored material upon UV irradiation) is obtained in the resulting matrix. The sol-gel matrix hinders the organic molecule rotations, thus giving two stable states, which can be reversibly switched by UV and green-blue irradiation respectively.If these materials are attached to optical fibers, the properties of the light throughput may be modified. Simple fiber-optic/photochromic devices made of two optical fibers placed in a V-groove removable connector have been prepared. Once cured, these devices behave as optically addressed variable delay generators. The same devices can be used for preparing simple optical switches and routing systems.     

Photoresponsive surfaces with controllable wettability

In this paper, current progress in the area of photoresponsive surfaces with controllable wettability is reviewed, including mainly surface conversion between wetting and anti-wetting, prepared from inorganic oxides (e.g., titanium dioxide, zinc oxide, and tungsten oxide) or/and photoactive organic molecules (e.g., azobenzene, and spiropyran), and movement of liquid droplets driven by molecular machines (e.g., molecular shuttles such as rotaxanes). Photoresponsive controllable wettability originates from a transition between the bistable states of photoresponsive materials. The exploration of the basic mechanisms provides a basis for the construction of novel smart responsive surfaces.     

Photo-and thermochromic spiranes. 29. New photochromic indolinospiropyrans containing a quinoline fragment

A new photochromic spiropyran of the indoline series, containing a quinoline fragment, has been synthesized. The photochromic properties of the spiropyran and its iodomethylate have been studied. Features of the molecular structure of the compounds were determined by X-ray structural investigations. It was established that the pyridopyran fragments of the cations in the crystal of the iodomethylate salt, unlike those in the crystal of the neutral spiropyran, emerge from 2₁-stacks, disposed jointly with I⁻ ions, which causes their higher mobility and aids the course of reversible photoconversions on UV irradiation in solution. For Part 28 see [1]. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 690–702, May, 2007.     

Light‐ and Solvent‐Controlled Self‐Assembly Behavior of Spiropyran–Polyoxometalate–Alkyl Hybrid Molecules

A molecular photochromic spiropyran–polyoxometalate–alkyl organic–inorganic hybrid has been synthesized and fully characterized. The reversible switching of the hydrophobic spiropyran fragment to the hydrophilic merocyanine one can be easily achieved under light irradiation at different wavelengths. This switch changes the amphiphilic feature of the hybrid, leading to a light‐controlled self‐assembly behavior in solution. It has been shown that the hybrid can reversibly self‐assemble into vesicles in polar solvents and irreversibly into reverse vesicles in non‐polar solvents. The sizes of the vesicles and the reverse vesicles are both tunable by the polarity of the solvent, with the hydrophobic interactions being the main driving force.     

Dipolar crystals produced photochemically

It is demonstrated that the microcrystals produced upon photochromic transformation of spiropyran in solution have permanent dipole moments which are formed spontaneously.     

Photostability of a photochromic naphthopyran dye in different sol-gel prepared ormosil coatings

A photochromic naphthopyran derivative was embedded in sol-gel prepared thin ormosil films. The resulting samples show high transparency and exhibit a strong red colouration upon irradiation with UV light. The photostability of the photochromic molecules is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the inner pore surface of the matrix allows tailoring the chemical environment where the dye molecules will be allocated, in terms of the effectiveness of the interaction between the photochromic molecules and the Si-OH groups on the surface of the pores, affecting the stability of the molecules upon prolonged exposition to UV light. The photostability of the molecules was increased in matrices functionalized with larger organic groups, or with larger amount of modifying groups. In this way the photodegradation of the photochromic molecules could be reduced by a factor of 5, as compared with the photodegradation of the molecules in unfunctionalized silica matrix.     

Stability against photodegradation of a photochromic spirooxazine dye embedded in amino-functionalized sol–gel hybrid coatings

A photochromic spirooxazine derivative, 1-propyl-3,3,5,6-tetramethyl-spiro[indoline-2-3??-[quinolino]oxazine], was successfully embedded in sol?Cgel thin silica films functionalized with different amino groups. The resulting films show high transparency and exhibit a strong blue coloration upon irradiation with UV light. The composition of the embedding matrix has an important effect on the photostability of the photochromic molecules upon exposure to sunlight, and can therefore be used to design coatings in which the dye molecules have improved durability. In this sense, the incorporation of different amino groups (?CPrNH₂, ?CPrNMe₂ and ?CPhNH₂) in the ormosil network, results in an enhanced stabilization of the photochromic dye, as compared with unfunctionalized matrices. In matrices modified with aminophenyl groups (?CPhNH₂), the photostability of the dye has been increased, reaching a factor of 8, due to the formation of hydrogen bonds between the amino groups and the OH groups of the pore surface, limiting the availability of these groups to undergo side reactions with the dye during irradiation that lead to its degradation. Increasing the photostability of the photochromic dye is an important issue for the long term usage of photochromic materials in outdoors applications, limited, nowadays, by their low durability when exposed to sunlight.     

Wetting properties of flat and porous silicon surfaces coated with a spiropyran

We report the immobilization and characterization of a spiropyran (SP) derivative (1) on smooth Si(100) and porous H-terminated silicon surfaces through a thermal hydrosilylation protocol. Under visible light exposure the SP is in a closed, hydrophobic form, whereas under UV irradiation it converts to a polar, hydrophilic open form named merocyanine (MC). The SP-MC photoinduced isomerization gives a small contact angle (CA) change of 9 degrees for smooth Si(100) samples under sequential irradiation cycles with white and UV light. Irradiation of porous silicon (PS) surfaces, under the same conditions, gave a CA change of 11 degrees. Treatment of PS surfaces, bearing the MC form of chromophore 1, with cobalt(II) ions enhances the wettability switching of the PS surface to a much larger extent, giving rise to a CA variation as high as 32 degrees.     

In situ Observation of the Photochromism in the Langmuir Monolayer of a Non—typical Amphiphilic Spiropyran Derivative at the Air／Water Interface

In situ photochromic process in the monolayer of aphotochromic spiropyran derivative without long alkyl chain,was investigated.The photochromism at the air/water interface under differnet surface pressures was studied by surface pressure-area isotherms,surface pressure-time curves,area-time curves and Brewster angle microscopy.Both forms of the compound were found to form monolayers at the air/water interface althouhg it does not have long alkyl chain.A large area expansion in the monolayer corresponding to a zreo^th order reaction was found at the initial stage of the UV light irradiation.A series of dynamic investigations revealed that at high pressure after phase transition in the monolayer,the surface pressure changes greatly umder alternative irradiation of UV and visible light.An obvious morphological change accompanying with the photochromism was observed in situ.     

Modified Electrodes and Electrochemical Systems Switchable by Light Signals

This article is an overview of extensive research efforts in many laboratories in the last two decades in the area of light‐switchable electrochemical systems and modified electrodes. Electrochemical reactions, including electrocatalytic and bioelectrocatalytic processes, have been reversibly activated and inhibited upon irradiation with light at different wavelengths. In order to realize these light activated or inhibited processes, the electrodes or/and reacting molecules were functionalized with photoisomerizable molecules including various derivatives of diarylethene, phenoxynaphthacenequinone, azobenzene and spiropyran/merocyanine. Photochemical reactions of these species resulted in change of their redox activity, conformation and electrical charge. All these changes affected electrode surfaces or (bio)molecules resulting in switching ON‐OFF corresponding (bio)electrochemical processes. Various systems based on different light‐controlled reactions are reviewed and discussed with specific examples and with many illustrating figures. Possible extensions of the research area and future applications are briefly overviewed in the conclusion section. The present comprehensive review is addressed to a broad scientific community, including newcomers to the area.     

Kinetic nonequivalence of spiropyran molecules during their photochromic conversions in Langmuir-Blodgett layers

The kinetics of the photochromic conversions of spiropyran molecules in Langmuir-Blodgett layers based on stearic acid were investigated. It was shown that the molecules of spiropyran are nonequivalent in their reactivity both in the reverse, dark stage and in the direct photochemical stage of the process. A correlation between the reactivity of the molecules in the direct and reverse reactions was demonstrated. The sign of the correlation was positive: the relatively more reactive spiropyran molecules in the direct photochemical reaction also remain more reactive in the reverse dark process. A physical model for the influence of the cell environment on the reactivity of the molecule, in which the effective relaxation of the structure of the cell environment following each event of the chemical conversion is proposed, was put forward.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2018–2024, September, 1991.