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.     

Photoswitchable Composite Polymer Electrolytes Using Spiropyran-Immobilized Nanoporous Templates

Composite polymer electrolytes (CPEs) with smart, stimuli-responsive characteristics have gained considerable attention owing to their noninvasive manipulation and applications in future technologies. To address this potential, in this work, we demonstrate photoresponsive composite polymer electrolytes, consisting of gel polymer electrolyte (GPE) and spiropyran-immobilized nanoporous anodic aluminum oxide (SP-AAO) templates. Under UV irradiation, the close SP form isomerizes to the open merocyanine (MC) form, creating extremely polarized AAO surfaces; whereas, under visible light irradiation, the MC form reverts to the SP form, creating neutral surface conditions. The electrostatic interactions between ions and AAO surfaces are investigated by attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. Moreover, the behavior of ionic conductivity of the GPE@SP-AAO is found to be consistent with the kinetics of isomerization tracked by UV-Vis spectroscopy. This work provides a promising platform for developing next-generation photoelectronic smart devices.     

Thermal hysteresis in the photoresponsivity of a langmuir film of amphiphilic spiropyran

We have found a thermal hysteresis in the photoresponsivity of a Langmuir film for the first time. The Langmuir film of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-1'-octadecyl-8-(docosanoyloxymethyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP) was fabricated at 13 degrees C at 10 mN m-1, followed by heating to a given temperature. UV irradiation of this film caused only the isomerization of SP to the corresponding merocyanine (MC) up to 29 degrees C. Light-induced J-aggregation of MC occurred at 30 degrees C. On the other hand, once the film was heated to 30 degrees C, light-induced J-aggregation was observed down to 27 degrees C. The hysteresis should be related with the phase transitions that occur in the bulk of SP at similar temperatures. No significant morphological change occurred by light-induced J-aggregation in the Langmuir-Blodgett (LB) film of SP by the present method, in contrast to the case of the LB films fabricated under isothermal conditions at 30 degrees C. This feature enabled us to pattern the LB film with J-aggregate of MC by UV irradiation through a photomask of lines with a width of 5 mum each.     

Photon control of liquid motion on reversibly photoresponsive surfaces

The movement of a liquid droplet on a flat surface functionalized with a photochromic azobenzene may be driven by the irradiation of spatially distinct areas of the drop with different UV and visible light fluxes to create a gradient in the surface tension. In order to better understand and control this phenomenon, we have measured the wetting characteristics of these surfaces for a variety of liquids after UV and visible light irradiation. The results are used to approximate the components of the azobenzene surface energy under UV and visible light using the van Oss-Chaudhury-Good equation. These components, in combination with liquid parameters, allow one to estimate the strength of the surface interaction as given by the advancing contact angle for various liquids. The azobenzene monolayers were formed on smooth air-oxidized Si surfaces through 3-aminopropylmethyldiethoxysilane linkages. The experimental advancing and receding contact angles were determined following azobenzene photoisomerization under visible and ultraviolet (UV) light. Reversible light-induced advancing contact-angle changes ranging from 8 to 16 degrees were observed. A large reversible change in contact angle by photoswitching of 12.4 degrees was achieved for water. The millimeter-scale transport of 5 microL droplets of certain liquids was achieved by creating a spatial gradient in visible/UV light across the droplets. A criterion for light-induced motion of droplets is shown to be consistent with the response of a variety of liquids. The type of light-driven fluid movement observed could have applications in microfluidic devices.     

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.     

Photo-isomerization of spiropyran-modified cationic surfactants

Photo-induced isomerization of a newly synthesized surfactant, 1'(6-trimethylammoniododecyl)-3('),3(')-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2'-indoline) bromide (SP-Me-12), has been characterized on the basis of the UV-vis absorption spectra and the surface tension data. Visible light (lambda>420 nm) incident on the aqueous solution of SP-Me-12 results in the isomerization from the merocyanine (MC) form to the spiropyran (SP) form; this structural change was confirmed by a complete disappearance of a characteristic absorption peak of the MC form. When the surfactant solution is stored in the dark, the isomerized SP form reverts to the original MC form, however, the reverse isomerization rate is observed to be considerably slower than that seen for visible light irradiation (from the MC form to the SP form). A reversible change in the surface tension of the aqueous surfactant solution is observed for the photo-induced isomerization: the surface tension measured below the critical aggregation concentration decreases as a result of the visible light irradiation and it is gradually reversed to the original level during the equilibration in the dark.     

Colorimetric sensing of cyanide anion in aqueous media with a fluorescein–spiropyran conjugate

A fluorescein–spiropyran conjugate (2) behaves as a receptor for colorimetric sensing of cyanide anion (CN^?) in aqueous media under irradiation of UV light. The compound 2, which exists as a spirocycle-closed (SP) form in the dark condition, is isomerized to the spirocycle-opened merocyanine (MC) form upon irradiation of UV light and shows absorption bands at 467 and 568 nm. Addition of CN^? to the solution leads to a decrease in these bands and an appearance of new absorption band at 512 nm, via a nucleophilic interaction between CN^? and the spirocarbon of MC form. This absorption change occurs selectively with CN^? and enables ratiometric quantification of CN^? by absorption analysis.     

Reversible photorheological fluids based on spiropyran-doped reverse micelles

We describe a new class of photorheological (PR) fluids whose rheological properties can be reversibly tuned by light. The fluids were obtained by doping lecithin/sodium deoxycholate (SDC) reverse micelles with a photochromic spiropyran (SP) compound. Initially, the lecithin/SDC/SP mixtures formed highly viscoelastic fluids, reflecting the presence of long, wormlike reverse micelles. Under UV irradiation, the SP was isomerized to the open merocyanine (MC) form, causing the fluid viscosity to decrease 10-fold. When the UV irradiation was switched off, the MC reverted to the SP form, and the viscosity recovered its initial value. This cycle could be repeated several times without loss of response. The rheological transitions are believed to reflect changes in the lengths of the reverse worms. To our knowledge, this is the first example of a simple, reversible PR fluid that can be made entirely from commercially available components.     

7-trifluoromethylquinoline-functionalized luminescent photochromic spiropyran with the stable merocyanine species both in solution and in the solid state

A new spiropyran (SP2) with the stable merocyanine form (MC2) both in solution and in the solid state at room temperature was designed and synthesized. The stability of MC2 is believed to be due to the electron-withdrawing effect of both the quinoline and the trifluoromethyl groups. (1)H NMR spectra indicate that the ratio of the open form vs the closed form of SP2 is dependent on the polarity of solvents. Single crystals composed of only the open form (MC2) were successfully obtained. X-ray structural analysis indicates that except trifluoromethyl and two methyl groups MC2 is completely planar with an s-trans,s-cis conformation. It should be noted that this is the first report of the X-ray crystal structure of the pure open form of spiropyran. MC2 can be slowly transformed into SP2 at -30 degrees C or lower temperature, and the process is accelerated by visible light irradiation. This special photochromic behavior can be explained by the calculated thermodynamic data. The spectral properties of SP2/MC2 in the presence of different metal ions are also studied, and the results show the potential application of SP2/MC2 in sensing metal ions.     

Covalently attached monolayers on crystalline hydrogen-terminated silicon: extremely mild attachment by visible light

A very mild method was developed for the attachment of high-quality organic monolayers on crystalline silicon surfaces. By using visible light sources, from 447 to 658 nm, a variety of 1-alkenes and 1-alkynes were attached to hydrogen-terminated Si(100) and Si(111) surfaces at room temperature. The presence and the quality of the monolayers were evaluated by static water contact angles, X-ray photoelectron spectroscopy, and IR spectroscopy. Monolayers prepared by thermal, UV light, or visible light initiation were compared. Additionally, the ability of infrared reflection-absorption spectroscopy to study organic monolayers on silicon was explored. A reaction mechanism is discussed on the basis of investigations of the reaction behavior of 1-alkenes with silicon wafers with varying types and levels of doping. Finally, a series of mixed monolayers derived from the mixed solutions of a 1-alkene and an omega-fluoro-1-alkene were investigated to reveal that the composition of the mixed monolayers was directly proportional to the molar ratio of the two compounds in the solutions.     

Characterization of thermal properties of porous silicon film/silicon using photoacoustic technique

We have applied photoacoustic (PA) technique to study the thermal properties of porous silicon (PS) films formed on p-type Si substrates by electrochemical anodic etching. Four PS samples with close thicknesses but greatly different porosities (from 20 to 60%) were examined. From the dependences of the PA signals on the modulation frequency of excitation light measured under a transmission detection configuration (TDC), effective thermal diffusivities for the two-layered PS/Si samples were determined and found to decrease greatly from 0.095 to 0.020 cm² s^-1 as the porosity increased from 20 to 60%. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spiropyran‐Conjugated Pluronic as a Dual Responsive Colorimetric Detector

Novel spiropyran‐conjugated Pluronic [polyethylene oxide (PEO)‐b‐polypropylene oxide (PPO)‐b‐polyethylene oxide (PEO)] micelles are developed as a new colorimetric detector showing photo‐ or thermo‐switchable behavior. Facile conjugation of spiropyran to Pluronic was confirmed by ¹H NMR, UV–Vis, and Fluorescence spectroscopy. A switchable photoluminescence is found depending on the irradiation with either UV or visible light, and temperature resulting from structural isomerization of spiropyran between spiropyran (SP) and merocyanine (MC) form. Cytotoxicity of the spiropyran‐conjugated Pluronic (SP‐PL) was evaluated following an MTT assay, whereas photo responsiveness of spiropyran within the micelles was determined by confocal laser scanning microscopy.     

Wetting behavior of porous silicon surfaces functionalized with a fulleropyrrolidine

We report the immobilization of a fulleropyrrolidine, bearing a dec-9-ynyl functionality, on silicon surfaces through a thermal hydrosilylation protocol. Contact angle measurements on porous silicon (PS) surfaces reveal an unusual dependence of the angle with the PS roughness that apparently contradicts Wenzel's formula. This result has been explained by an extension of Wenzel's model in which the critical angle, which discriminates between the hydrophilic/hydrophobic character of a solid material, is substantially reduced below 90 degrees by surface roughness.     

Effect of current density on morphological,structural and optical properties of porous silicon

The morphology of porous silicon (PS) layers produced by electrochemical etching of n-type (100) silicon (Si) at different low current densities was studied using SEM, image J analysis and WSxM software. From FTIR spectroscopy analysis, the Si dangling bonds of the as-prepared PS layer have large amount of Hydrogen to form weak Si–H bonds. From Raman analysis, a full width half maximum (FWHM) of the Raman peak was gradually increased with increased current density, shifted towards lower energies due to reduce of crystallite size, the crystallite size in the PS varied from 63 nm to 20 nm depending on the current density. The optical response of the PS layer has been performed by the absorbance and Photoluminescence was studied experimentally in the visible range. The optical absorption and photo luminescence in PS is due to excitonic recombination between the defect states as well as on the surface of nanocrystals, and this was attributed to the presence of silicon hydride species which are confirmed by FTIR spectra. The red shift was observed in absorbance and Photoluminescence due to decrease in the size of Si crystallites and growth of Si=O bonds. The contact angle varied from 76° to 120.1°. From the wettability studies, the surface nature of the PS was converted from hydrophilic to hydrophobic when the current density increased.     

氧化钒/多孔硅/硅结构的微观形貌、纳米力学及温敏特性

采用电化学腐蚀法在硅基片表面形成多孔硅, 利用直流对靶反应磁控溅射方法在不同电流密度条件下制备的多孔硅样品表面上溅射沉积了VOx薄膜, 获得了氧化钒/多孔硅/硅(VOx/PS/Si)结构. 采用场发射扫描电镜(FESEM)观测多孔硅及VOx/PS/Si结构的微观形貌, 采用纳米压痕仪器测量VOx/PS/Si结构的纳米力学特性, 通过电阻-功率曲线分析研究其温度敏感特性. 实验结果表明, 在40和80 mA·cm-2电流密度下制备多孔硅的平均孔径分别为18和24 nm, 用显微拉曼光谱法(MRS)测量其热导率分别为3.282和1.278 kW·K-1; VOx/PS/Si结构的电阻随功率变化的平均速率分别为60×10⁹和100×10⁹ Ω·W-1, VOx/PS/Si结构的显微硬度分别为1.917和0.928 GPa. 实验结果表明, 多孔硅的微观形貌对VOx/PS/Si结构的纳米力学及温敏特性有很大的影响, 大孔隙率多孔硅基底上制备的VOx/PS/Si 结构比小孔隙率多孔硅基底上制备的具有更高的温度灵敏度, 但其机械稳定性也随之下降.     

Zinc chelation and photofluorochromic behavior of spironaphthoxazine intercalated into hydrophobically modified montmorillonite

Spironaphthoxazine (SNO) and Zn2+ were intercalated into montmorillonite interlayers hydrophobically modified by the alkyltrimethylammonium cation during UV light irradiation. The fluorescence spectra of the montmorillonite composites were observed to vary with an increase in the UV and visible light irradiation times. These composites exhibited two types of fluorescence emissions: F1, which originates from a new species, Xs, which is different from SNO (ring-closed form) and merocyanine (MC; ring-open form), and F2, which originates from the MC-Zn complex. With increasing UV light irradiation time, the F1 intensities decreased, whereas the F2 intensities increased. Xs, which is an intermediate species between SNO and MC, was transformed into MC and then coordinated with Zn2+ (i.e., MC-Zn complex) during the UV light irradiation. The reaction rate of the formation of the MC-Zn complex decreased for the hydrophobically modified montmorillonite due to a longer alkyl chain. The retrieval changes in the F1 and F2 intensities were observed with an increasing visible light irradiation time, implying the dissociation of the MC-Zn complex into Xs and Zn2+. The dissociation especially occurred for the hydrophobically modified montmorillonite with a longer alkyl chain. The formation and disappearance of Xs and the MC-Zn complex obeyed first-order kinetics, and therefore the interconversion between Xs and MC could be regarded as the rate-determining step of the whole reaction during the UV and visible light irradiations. The photoinduced reactions of the SNO species and Zn2+ were profoundly affected by the physicochemical environment provided by the clay interlayers. It is concluded that the present photoreactions can be controlled not only by the amounts of the intercalated SNO species and Zn2+, but also by the hydrophobic environment created by the surfactant molecules.     

Conductance Photoswitching of Metal–Organic Frameworks with Embedded Spiropyran

Conductive metal–organic frameworks (MOFs) as well as smart, stimuli‐responsive MOF materials have attracted considerable attention with respect to advanced applications in energy harvesting and storage as well as in signal processing. Here, the conductance of MOF films of type UiO‐67 with embedded photoswitchable nitro‐substituted spiropyrans was investigated. Under UV irradiation, the spiropyran (SP) reversibly isomerizes to the open merocyanine (MC) form, a zwitterionic molecule with an extended conjugated π‐system. The light‐induced SP–MC isomerization allows for remote control over the conductance of the SP@UiO‐67 MOF film, and the conductance can be increased by one order of magnitude. This research has the potential to contribute to the development of a new generation of photoelectronic devices based on smart hybrid materials.     

Self-assembled Alkylation of Atomically Flat Hydrogen-terminated Silicon (111) Surface By Using Highly Polarized Fluoroalkylsilane

Hydrogen-terminated silicon surface is of technological importance to semiconductor processes such as pre-gate^[1]. Re-contamination and re-oxidation on silicon surface become more stringent issues in order to meet the requirements in the process for producing reduced size IC chips. The modification of silicon surfaces by various strategies has attracted more attention in the past few years^[2-4]. The frequently used techniques to attach functional groups to silicon surfaces are via chemical^[2], photochemical^[3] and electrochemical reactions^[4]. Various ways to attach monlayers to silicon surfaces has been reported, including alkylation of silicon with alkenes, alkyenes, aldehydes, alcohols and Grigard reagents under photoactivated or catalytic reactions. Particularly, porous silicon prepared by chemical or electrochemical treatments has been extensively studied. Preparation of passivated layers on porous silicon surfaces has disadvantages that the silicon surfaces are damaged by reactive agents during the reaction or become porous for attachment of molecules. Recently, self-assembled monolayer of alcohols on porous silicon was reported at modest heating without the aid of catalyst or photoexcitation or potential^[5]. In the paper, we report a novel method to attach highly polarized fluoroalkylsilane on atomically flat Si(111) surface at room temperature and to form a self-assembled monolayer to prevent the silicon surface from re-contamination and re-oxidation.     

Hydrophobic anatase TiO(2)-based thin films modified with Al, Cr derivatives to reach reversible wettability control

Polycrystalline anatase TiO(2)-based thin films with surface roughness were fabricated using a sublimation method. Their surfaces showed hydrophobicity with a water contact angle (CA) higher than 130 degrees when stored in the dark. For the films, the hydrophobic conversion behavior and critical CA depended on surface morphologies. The higher hydrophobic conversion rate and higher critical CA were explained by the smaller r in the Wenzel equation and the smaller f (f = 0.56, 0.30) in the Cassie equation, respectively. Moreover, good reversibility between hydrophobicity (CA = 130 degrees ) and high hydrophilicity (CA = 0 degrees ) was observed by alternating between UV light irradiation and dark storage. The combination of chromium oxide with anatase TiO(2) markedly shortens the period of hydrophobic conversion from 12 to 5 days.     

TiO2颗粒在羟基表面的沉积行为及图案化

比较了3种具有羟基表面SiO2层的差异:紫外光照SAMs形成的羟基表面,紫外光照射前、照射后的羟基表面;用光照前后表面的差异,结合化学浴沉积技术在单晶硅基底上制得了TiO2微图案薄膜。系统考察了光源、硅片表面性质的变化、溶液等方面对图案生成的影响。实验表明TiO2沉积在未照区,电子和空穴动力学上的差异造成光照区表面正电荷增多,抑制了TiO2的沉积。该方法不需要光刻胶和自组装膜作为辅助模板,具有简单廉价的特点。