Photochromic Devices Research Articles

Fabrication of molybdenum trioxide (MoO3) coating by electrophoretic deposition

Due to great potential in applications involving gas sensors, catalysts in electrochemistry, photochromic and electrochromic devices, extensive research has been conducted on fabricating molybdenum trioxide (MoO3) coating. In this study, MoO3 nanoparticles (~100 nm) synthesized by a hydrothermal method was employed as starting materials to develop coatings via electrophoretic deposition (EPD) methods. An ethanol solution containing 0.1 mM sodium hydroxide was employed as the suitable solvent for EPD of MoO3 nanoparticle. The coating growth rate was varied by different deposition times in the range of 1–20 min at voltages of 50–150 V. Results of this study demonstrate that EPD is a feasible method of fabricating MoO3 coating which is of potential interest in applications of gas sensors, catalysts and electrochromic and photochromic devices.

Excitation energy deactivation funnel in 3-substituted BODIPY-porphyrin conjugate

BODIPYs absorb in the visible region which is complementary to that of porphyrins and therefore can be suggested as promising antenna groups to improve the light-harvesting potential of porphyrins. A boron-dipyrromethene dye was combined at the 3-position with a Zn-porphyrin to afford a conjugate. The fluorescence of the conjugate was found to originate from the BODIPY moiety independently of the excitation wavelength due to an unique set of energy transfer rates between the BODIPY and Zn-porphyrin moieties. The fluorescence intensity was shown to be tunable over a wide range using the solvent properties. This feature makes the studied BODIPY-porphyrin conjugate a promising compound for the design of new photochromic devices.

Cubic WO3 stabilized by inclusion of Ti: Applicable in photochromic glazing

We report on the development of WO3 layers with increased symmetry induced by the incorporation of titanium into a crystalline WO3 matrix. The atomic ratio between W and Ti was varied stepwise from 100:1 to 100:20 with pure WO3 layers, made using peroxo sol–gel synthesis, as a reference. Layers were then formed by dip-coating from the corresponding sols. IR spectroscopy and XRD analysis of layers and powders heat-treated at 450°C proved that the presence of titanium ions induces ordering and increases the symmetry of WO6 octahedra in the WO3 crystalline matrix leading to the transformation of the cell symmetry from monoclinic through tetragonal up to the cubic. Cyclic voltammetry confirmed that this increased symmetry leads to an up-shift in redox potential, which favors the coloration of the layers in photochromic devices. According to our knowledge, this is the first report of colorless cubic WO3 layers, which have potential applications in optoelectronic devices and sensors.

An acido- and photochromic molecular device that mimics triode action.

The photo-controlled shift of pH titration curves, describing the acidochromic behaviour of a spiropyran switch network, was harnessed for the realisation of a molecular triode. The intricate network can be correctly interpreted with respect to the pH dependence of the main involved species.

Reversible chemochromic MoO3 nanoribbons through zerovalent metal intercalation.

Molybdenum trioxide (α-MoO3) is a 2D layered oxide with use in electrochromic and photochromic devices owing to its ability to reversibly change color between transparent and light blue with electrochemical or hydrogen intercalation. Despite its significant application potential, MoO3 performance is largely limited by the destructiveness of these intercalation techniques, insignificant coloration, and slow color response. We demonstrate a reversible chemochromic method, using intercalation of zerovalent metals into α-MoO3 nanoribbons (Sn, ∼2 at. %; Co, ∼4 at. %), to chemically alter MoO3 from transparent white to a deep blue indigo, resulting in enhanced coloration and chemically tunable optical properties. We present two strategies to reversibly tune the color response of MoO3 nanoribbons. Chromism can be reversed (i) by complete oxidative deintercalation with hydrogen peroxide or iodine or (ii) through a temperature-driven disorder-order phase transition of the intercalated zerovalent metal.

Photochromic molecular implementations of universal computation

Unconventional computing is an area of research in which novel materials and paradigms are utilised to implement computation. Previously we have demonstrated how registers, logic gates and logic circuits can be implemented, unconventionally, with a biocompatible molecular switch, NitroBIPS, embedded in a polymer matrix. NitroBIPS and related molecules have been shown elsewhere to be capable of modifying many biological processes in a manner that is dependent on its molecular form. Thus, one possible application of this type of unconventional computing is to embed computational processes into biological systems. Here we expand on our earlier proof-of-principle work and demonstrate that universal computation can be implemented using NitroBIPS. We have previously shown that spatially localised computational elements, including registers and logic gates, can be produced. We explain how parallel registers can be implemented, then demonstrate an application of parallel registers in the form of Turing machine tapes, and demonstrate both parallel registers and logic circuits in the form of elementary cellular automata. The Turing machines and elementary cellular automata utilise the same samples and same hardware to implement their registers, logic gates and logic circuits; and both represent examples of universal computing paradigms. This shows that homogenous photochromic computational devices can be dynamically repurposed without invasive reconfiguration. The result represents an important, necessary step towards demonstrating the general feasibility of interfacial computation embedded in biological systems or other unconventional materials and environments.

Synthesis of photochromic 5,6-diaryl-2-chloropyridine-3,4-dicarbonitriles from 3,4-diaryl-4-oxobutane-1,1,2,2-tetracarbonitriles

We now propose a new synthetic approach to photochromic diarylethenes, which is based on the reaction of tetracyanoethylene with ketones as key intermediate step. Tetracyanoethylation of ketones has been well documented; however, there are almost no published data on reactions of aryl arylmethyl ketones with tetracyanoethylene. Adducts of tetracyanoethylene with ketones of the general formula R(CO)CH2R′ were used as starting compounds to obtain heterocycles containing an RC=CR′ fragment [4–10]. Analogous reactions with aryl arylmethyl ketones Ar(CO)CH2Ar could give rise to various 1,2-diarylethenes as new potential photochromes. We were the first to react tetracyanoethylene with 1,2-diarylethanones Ia and Ib in the presence of a catalytic amount of hydrochloric acid. As a result, we isolated 3,4-diaryl-4-oxobutane-1,1,2,2-tetracarbonitriles IIa and IIb. The substrates were deoxybenzoin (Ia), the parent compound of the 1,2-diarylethanone series, and 1,2-bis(2,5-dimethylthiophen-3-yl)ethanone (Ib). The latter was selected taking into account that diarylethenes containing thienyl substituents are most promising from the viewpoint of the design of practically useful photochromic devices [1]. Ketone Ib was synthesized in a number of steps starting from hexane2,5-dione [11].

Lithium Based Ionogel as Solid State Electrolyte: Dynamics of Confined Ionic Liquid, a Neutron Diffusion Study

Ionic liquids (ILs) have been the focus of a rapidly growing number of studies in materials science since early 2000’s. Their liquid state is advantageous for their properties but often prevents their applications in devices which most often need solid state shaping. Thus, several approaches to get round this drawback are under investigation. Polymerizing the IL, grafting any of its ions onto a substrate, making physical gels … We have focused our work on confining IL in host matrices, resulting in solid materials, as well as leaving the dynamics features of the liquid state. The host matrix can be either fully inorganic, mixed polymeric and inorganic or fully polymeric. In each case, there is a continuous silica-to-IL interface, where silica has been obtained through sol-gel route. The solid obtained is thus endowed with properties of the choosen IL simultaneously with those of a robust host backbone including a silica interface.The resulting ionogels, fully inorganic, mixed polymeric and inorganic or fully polymeric, are showing striking properties. The synergetic associations allow most often to lower the melting point of IL as well as to increase the ionic transport. It will be shown that the continuous interface and the confinement at nanoscale are modifying advantageously intensive properties of ILs. The conclusions are supported by results of studies with local probes (NMR, QENS, relaxometry, PGSE) and macroscopic measurements (CIS, BDS, DSC, IR) which show complementary information on chemistry, texture and physics (charge transport, dynamics, transmittance, dielectric …).Among several potential applications, we are focusing on supercaps, lithium batteries, electrochromic and photochromic devices. The macroscopic observation of the properties of these solid devices shows either equal or superior properties as referred to genuine ILs.

Density functional theory study of the conformation and optical properties of hybrid Au(n)-dithienylethene systems (n = 3, 19, 25).

We present a theoretical study of Aun-dithienylethene hybrid systems (n = 3, 19, 25), where the organic molecule is covalently linked to a nanometer-scaled gold nanoparticle (NP). We aim at gaining insights on the optical properties of such photochromic devices and proposing a size-limited gold aggregate model able to recover the optical properties of the experimental system. We thus present a DFT-based calculation scheme to model the ground-state (conformation, energetic parameters) and excited-state properties (UV-visible absorption spectra) of this type of hybrid systems. Within this framework, the structural parameters (adsorption site, orientation, and internal structure of the photochrome) are found to be slightly dependent on the size/shape of the gold aggregate. The influence of the gold fragment on the optical properties of the resulting hybrid system is then discussed with the help of TD-DFT combined with an analysis of the virtual orbitals involved in the photochromic transitions. We show that, for the open hybrid isomer, the number of gold atoms is the key parameter to recover the photoactive properties that are experimentally observed. On the contrary, for hybrid closed systems, the three-dimensional structure of the metallic aggregate is of high impact. We thus conclude that Au25 corresponds to the most appropriate fragment to model nanometer-sized NP-DTE hybrid device.

Steering the excited state dynamics of a photoactive yellow protein chromophore analogue with external electric fields

The first excited state of the Photoactive Yellow Protein chromophore exhibits a strong charge transfer character and the dipole moments of the excited and ground states differ significantly. Furthermore, the excited state charge distribution changes during the isomerization of this chromophore. These observations suggest that external electric fields can be used to control photo-isomerization, providing a new concept for developing photochromic devices, such as e-paper or optical memory. To test this idea, we performed excited state dynamics simulations and static calculations of a PYP chromophore analogue (pCK−) in an external electric field. By adjusting direction and strength of the field, we were able to control both selectivity (i.e., which bond isomerizes) and efficiency (excited state lifetime) of the isomerization process. Simulations like these could potentially be useful in validating whether a given chromophore could be suitable for electrochromic applications.

Hybrid photochromic multilayer films based on chitosan and europium phosphomolybdate

Multilayer films based on chitosan and K11[EuIII(PMo11O39)2] were prepared on different substrates using the layer-by-layer method. UV–Vis spectra of the films showed regular stepwise growth. X-ray photoelectron spectroscopy data confirmed the presence of chitosan and phosphomolybdate within the films and scanning electron microscopy images revealed a completely covered surface with a roughened texture. The film electrochemical responses and permeability were studied by cyclic voltammetry. Films revealed four surface-confined Mo-based reduction processes (MoVI → MoV). Studies with [Fe(CN)6]3−/4− and [Ru(NH3)6]3+/2+ showed that film permeability depended on the film thickness and on the charge of the outer layer. Irradiation of films with UV light confirmed their photochromic properties through the colour change from transparent to blue. Colouration–discolouration cycles could be repeated up to 36 cycles without the loss of optical contrast, indicating high film photochromic stability. These results provided valuable insights for exploring the potential application of polyoxometalate-based films for the construction of photochromic devices.

Erratum to: Sol–gel synthesis of mesoporous WO3–TiO2 composite thin films for photochromic devices

Mesoporous WO3–TiO2 composite films were prepared by a sol gel based two stage dip coating method and subsequent annealing at 450, 500 and 600 °C. An organically modified silicate based templating strategy was adopted in order to obtain a mesoporous structure. The composite films were prepared on ITO coated glass substrates. The porosity, morphology, and microstructures of the resultant products were characterized by scanning electron microscopy, N2 adsorption–desorption measurements, μ-Raman spectroscopy and X-ray diffraction. Calcination of the films at 450, and 500 °C resulted in mixed hexagonal (h) plus monoclinic phases, and pure monoclinic (m) phase of WO3, respectively. The degree of crystallization of TiO2 present in these composite films was not evident. The composite films annealed at 600 °C, however, consist of orthorhombic (o) WO3 and anatase TiO2. It was found that the o-WO3 phase was stabilized by nanocrystalline anatase TiO2. The thus obtained mesoporous WO3–TiO2 composite films were dye sensitized and applied for the construction of photochromic devices. The device constructed using dye sensitized WO3–TiO2 composite layer heat treated at 600 °C showed an optical modulation of 51 % in the NIR region, whereas the devices based on the composite layers heat treated at 450, and 500 °C showed only a moderate optical modulation of 24.9, and 38 %, respectively. This remarkable difference in the transmittance response is attributed to nanocrystalline anatase TiO2 embedded in the orthorhombic WO3 matrix of the WO3–TiO2 composite layer annealed at 600 °C.

Self‐Assembled Ultrathin Anatase TiO2 Nanosheets with Reactive (001) Facets for Highly Enhanced Reversible Li Storage

Nanostructued TiO2 polymorphs have attracted attention as promising materials for photocatalysis, solar cells, photochromic devices, gas sensors, surface coatings and energy-storage applications, particularly for Li-ion batteries (LIBs), which are well-known electrochemical energy-storage systems that have dominated in many miniature electronic appliances. Moreover, various polymorphs of TiO2, such as anatase, rutile and monoclinic phases, have been widely investigated as prospective anode materials for LIBs because of their good rate capability and the absence of lithium platting issues during highcurrent operation, and because solid electrolyte interfaces (SEIs) are unlikely to be formed, compared to graphitic anodes. However, their poor reversibility (0.5 moles of Li), higher operating potential and lower theoretical capacity (335 mAhg ) compared to graphitic anodes (372 mAhg) is a drawback of titanate anodes. Tuning the structural (orientation of the crystals) and morphological aspects of anatase phase is reported to be a noteworthy approach to realize its theoretical capacity with high reversibility. Apart from the synthesis technique, there are several attempts, such as carbon coating, composite with carbonaceous materials, metal doping and integrated structure with other transition metal oxides, that are reported to increase the reversibility beyond 0.5 moles of Li per formula unit. 11–13] However, the aforementioned approaches provide only a marginal improvement in the reversibility. Another approach to enhance the reversibility without significantly affecting the volumetric capacity is the utilization of high-surface-energy facets. In the case of the anatase phase, the (001) facets exhibit a high reactivity because of their higher surface energy (0.90 Jm ) compared to the (100) facets (0.44 Jm ) and the thermodynamically more stable (101) facets (0.53 Jm ). This clearly shows that Li diffusion is more favored along the (001) direction rather than along the (101) direction, and the Li diffusion coefficients are approximately found to be (2.0 0.8) 10 13 and (7 2) 10 14 cms , respectively, as reported by Hengerer et al. Therefore, research is devoted to engineering the utilization of high-energy (001) facets for prospective LIB anodes with high reversibility and morphological features. However, few reports are available on the utilization of such high-energy facets for LIB anodes; for example, Sun et al. reported an initial discharge capacity of ~200 mAhg 1 for (001) facets at a current density of 167 mAg 1 with severe capacity fading. Chen et al. reported the assembly of hierarchical microspheres consisting of (001) facets and delivered a first discharge capacity of ~204 mAhg 1 at a current density of 170 mAg 1 with capacity fading. Hence, there is a continuing effort anticipated for highly exposed (001) facets to enhance the Li reversibility during electrochemical cycling, since the observed values from the literature are more or less the same as that of conventional nanostructured anatase phase (~0.5 moles of Li). In this line, we made an attempt to employ highly exposed (001) facets of anatase phase TiO2 nanosheets by a conventional hydrothermal approach and subsequently assembled them together as a stack to increase the Li-ion reversibility. A half-cell assembly is conducted to evaluate the Li-storage properties of self-assembled and asprepared (non-assembled) TiO2 nanosheets of (001) facets ; these are described in detail.

Multiple Pathways for the Primary Step of the Spiropyran Photochromic Reaction: A CASPT2//CASSCF Study

CASSCF and CASPT2 studies on the reaction mechanism of the photochromic ring-opening process of a spiropyran (SP) (1',3',3'-trimethylspiro-[2H-1-benzopyran-2,2'-indoline], also known as BIPS) have been performed and possible excited-state C-O (and C-N) bond cleavage pathways and S1-to-S0 nonadiabatic transition channels have been explored. (1) The C-O bond dissociation in SP does not follow a conical-intersection mechanism that has been proposed in a model study with a simplified benzopyran. The CASSCF-optimized crossing points are actually avoided crossings with a large S1-S0 energy gap at the CASPT2 level; thus, they could not act as efficient S1-to-S0 funnels. (2) C-O bond cleavage paths on S1 leading to both the CCC (cis-cis-cis with respect to the configuration around α, β, γ) and TCC (trans-cis-cis) intermediates of merocyanine (MC) are barrierless, in line with the experimentally observed ultrafast formation of MC. (3) An unexpected low-energy hydrogen-out-of-plane (HOOP) valley on the (π→σ*) surface was located not far from the C-O bond cleavage path and was suggested to be an efficient S1-to-S0 nonadiabatic decay channel. Triggered by the active HOOP mode, the molecule can easily access the S1-HOOP valley and then make a transition to the S0 surface through the narrow S1-S0 gap that exists in an extended region. Nonadiabatic decay through a conical intersection on C-N dissociation path as well as the HOOP funnel is responsible for high internal conversion yields of SP. These findings shedding light on the complex mechanism of SP-MC interconversion provide fundamental information for design spiropyran-based photochromic devices.

Sol–gel synthesis of mesoporous WO3–TiO2 composite thin films for photochromic devices

Mesoporous WO3–TiO2 composite films were prepared by a sol gel based two stage dip coating method and subsequent annealing at 450, 500 and 600 °C. An organically modified silicate based templating strategy was adopted in order to obtain a mesoporous structure. The composite films were prepared on ITO coated glass substrates. The porosity, morphology, and microstructures of the resultant products were characterized by scanning electron microscopy, N2 adsorption–desorption measurements, μ-Raman spectroscopy and X-ray diffraction. Calcination of the films at 450, and 500 °C resulted in mixed hexagonal (h) plus monoclinic phases, and pure monoclinic (m) phase of WO3, respectively. The degree of crystallization of TiO2 present in these composite films was not evident. The composite films annealed at 600 °C, however, consist of orthorhombic (o) WO3 and anatase TiO2. It was found that the o-WO3 phase was stabilized by nanocrystalline anatase TiO2. The thus obtained mesoporous WO3–TiO2 composite films were dye sensitized and applied for the construction of photochromic devices. The device constructed using dye sensitized WO3–TiO2 composite layer heat treated at 600 °C showed an optical modulation of 51 % in the NIR region, whereas the devices based on the composite layers heat treated at 450, and 500 °C showed only a moderate optical modulation of 24.9, and 38 %, respectively. This remarkable difference in the transmittance response is attributed to nanocrystalline anatase TiO2 embedded in the orthorhombic WO3 matrix of the WO3–TiO2 composite layer annealed at 600 °C.

Tri-ureasil gel as a multifunctional organic–inorganic hybrid matrix

We report on a novel transparent, flexible, rubbery, and insoluble tri-ureasil organic–inorganic hybrid material with multifunctional characteristics and potential application in drug delivery, water purification, and photochromic materials. We obtained the tri-ureasil gels by the one-pot sol–gel route using 3-isocyanatopropyltriethoxysilane and glyceryl poly(oxypropylene)triamine of molecular weight 5000 g mol−1 (Jeffamine® T5000). This approach generated a silica backbone covalently connected with poly(oxyalkylene) chains PPO(OCH–CH3CH2)n through urea bridges. We characterized the obtained materials by DSC, swelling tests, XRD, 29Si NMR, and small-angle X-ray scattering (SAXS). The results attested that the tri-ureasil hybrids are potentially applicable as photochromic devices, drug delivery systems, and adsorbents of pollutants from contaminated waters.

Raman studies of hexagonal MoO3 at high pressure

AbstractThe transition‐metal oxide MoO3 is an important semiconductor and has various technological applications in catalysts, electrochromic and photochromic devices, gas sensors, and battery electrodes. In this study, the hexagonal MoO3 prepared by a hydrothermal method is in morphology of microrod with diameter of 0.8–1.2 µm and length of 2.0–4.3 µm. Its structural stability was investigated by an in situ Raman scattering method in a diamond anvil cell up to 28.7 GPa at room temperature. The new Raman peak around 1000 cm−1 implies that a phase transition from hexagonal to amorphous starts at 5.6 GPa, and the evolution of the Raman spectra indicates that the structural transition is completed at about 13.2 GPa. After releasing pressure to ambient condition, the Raman spectrum pattern of the high pressure phase was retained, revealing that the phase transition is irreversible.

Porous orthorhombic tungsten oxide thin films: synthesis, characterization, and application in electrochromic and photochromic devices

Porous orthorhombic tungsten oxide (o-WO3) thin films, stabilized by nanocrystalline anatase TiO2, are obtained by a sol–gel based two stage dip coating method and subsequent annealing at 600 °C. An Organically Modified Silicate (ORMOSIL) based templating strategy is adopted to achieve porosity. An asymmetric electrochromic device is constructed based on this porous o-WO3 layer. The intercalation/deintercalation of lithium ions into/from the o-WO3 layer of the device as a function of applied coloration/bleaching voltages have been studied. XRD measurements show systematic changes in the lattice parameters associated with structural phase transitions from o-WO3 to tetragonal LixWO3 (t-LixWO3) and a tendency to form cubic LixWO3 (c-LixWO3). These phase transitions, induced by the Li ions, are reversible, and the specific phase obtained depends on the quantity of intercalated/deintercalated Li. Raman spectroscopy data show the formation of t-LixWO3 for an applied potential of 1.0 V and the tendency of the system to transform to c-LixWO3 for higher coloration potentials. Optical measurements show excellent contrasts between colored and bleached states. An alternate photochromic device was constructed by sensitizing the o-WO3 layer with a ruthenium based dye. The nanocrystalline anatase TiO2 in the o-WO3 layer has led to an enhanced photochromic optical transmittance contrast of ∼51% in the near IR region. The combination of the photochromic and electrochromic properties of the synthesised o-WO3 layer stabilized by nanocrystalline anatase TiO2 opens up new vista for its application in energysaving smart windows.

Photochromic polymers bearing various diarylethene chromophores as the pendant: synthesis, optical properties, and multicolor photochromism

Photochromic polymers with various diarylethene derivatives were synthesized by a conventional radical polymerization of styrene derivatives having diarylethene chromophores as the pendant. All the polymers exhibited reversible photochromism in the film as well as in solution, while the photocyclization conversion in the film decreased in comparison with that in solution because of a restriction of the conformational structure in the solid state. Although the photocyclization and photocycloreversion quantum yields at the initial stage of the reactions in the film were comparable to those in solution, the apparent cycloreversion quantum yield decreased along with the reaction, which is derived from a distribution of the quantum yields in the solid state. Finally, the photochromic terpolymers consisting of three diarylethene monomers which show photochromism changing color to cyan, magenta, and yellow were synthesized. The terpolymers were demonstrated to show bright colors including black, green, red, and blue both in solution and in the solid state by selective bleaching processes. Such multicolor photochromic polymers composed of diarylethene derivatives have a potential for rewritable photochromic display devices.

Block copolymer-templated synthesis of highly organized mesoporous TiO 2-based films and their photoelectrochemical applications

Over the last decade, mesoporous TiO 2 nanocrystalline films have been intensively investigated not only for fundamental research interest but also for technological applications. This critical review summarizes recent progress of the block copolymer-templated highly organized mesoporous TiO 2-based films prepared via an evaporation-induced self-assembly (EISA) process and their photoelectrochemical applications. With a brief introduction to the principle of block copolymer self-assembly and EISA process, control of the cooperative self-assembly between Ti species and block copolymer in the sol solution as well as in the deposited films, aging under a controlled humid environment, and subsequent thermal treatment is described. Key experimental parameters for the preparation of highly organized mesoporous TiO 2 films are analyzed. Applications of mesoporous TiO 2-based films in photocatalytic reactions, catalytic chemical synthesis, dye-sensitized solar cells, and electrochromic and photochromic devices are discussed. The synthesis-component-structure-property relationship in mesoporous TiO 2-based films is highlighted, and the perspectives in this rapidly developing field are suggested.