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.     

Effect of the chemical environment on the light-induced degradation of a photochromic dye in ormosil thin films

The naphthopyran (NP) derivative (3-(2,4-dimethoxyphenyl)-3-(4-methoxyphenyl)-3H-naphtho[2,1-b]pyran) exhibits photochromism in solution or embedded in solid matrices. The molecule suffers a progressive photodegradation upon prolonged irradiation with UV-light, which depends strongly on the solvent or the embedding matrix. The photodegradation of the dye molecules in THF or benzene solutions is much faster than that of the molecules embedded in solid matrices (polymer or ormosil).The organic functional groups incorporated in the network of the ormosil matrix play an important role in the photostability of the dye, as they determine the chemical environment of the dye molecules in the matrix. In this way, the dye embedded in matrices whose inner pore surface is functionalized with phenyl groups exhibits a photostability nine times higher than in unmodified matrices, being their degradation half-life (t_1/2(deg)) 181 h and 21 h, respectively. The photostability of the photochromic dye in the ormosil matrices was also measured as a function of the dye loading, showing higher stability as the amount of dye is increased. The photostability of the dye in photochromic materials is an important issue in sight of the possible applications of these materials, as the performance of the devices involves repeated exposure to UV radiation.     

Nanoarchitecture self-assembly and photochromic studies of 2,2-diarylnaphthopyrans

The synthesis and photochromic properties of novel 2,2-diarylnaphthopyrans were described. Significantly, the nanostructured architecture through two-component self-assembly of a photochromic naphthopyran and an asymmetric biphenyl was determined by X-ray diffraction. The structure motifs of nanocavities were formed by Cl?O interactions and Ar-H?Cl hydrogen bonds among the photochromic naphthopyran molecules. It was further shown by TEM that the dimensions of cavity structures were up to nanometer level, which provides the potential to capture useful nanoscale entities and control photochromism in organic materials.     

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.     

萘并吡喃光致变色荧光开关研究进展

萘并吡喃及其衍生物是经典的光致变色材料,具有很低的背景颜色、优良的光致变色抗疲劳性、易于调控的变色动力学、开环体具有宽的吸收等优点,受到了研究者的重视。本文综述了近几年来作者课题组利用萘并吡喃构建光致变色荧光开关的研究进展,通过将荧光基团和萘并吡喃以掺杂模式、共聚物和有机小分子等形式构建光致变色荧光开关,研究了它们在溶液和薄膜中的荧光开关性能,初步探讨了萘并吡喃荧光开关在非破坏性读出和荧光成像等方面的应用潜能。     

Tuning the optical properties of mesoporous TiO2 films by nanoscale engineering

The optical properties of spin-coated titanium dioxide films have been tuned by introducing mesoscale pores into the inorganic matrix. Differently sized pores were templated using Pluronic triblock copolymers as surfactants in the sol-gel precursor solutions and adjusted by varying the process parameters, such as the polymer concentration, annealing temperature, and time. The change in refractive index observed for different mesoporous anatase films annealed at 350, 400, or 450 °C directly correlates with changes in the pore size. Additionally, the index of refraction is influenced by the film thickness and the density of pores within the films. The band gap of these films is blue-shifted, presumably due to stress the introduction of pores exerts on the inorganic matrix. This study focused on elucidating the effect different templating materials (Pluronic F127 and P123) have on the pore size of the final mesoporous titania film and on understanding the relation of varying the polymer concentration (taking P123 as an example) in the sol-gel solution to the pore density and size in the resultant titania film. Titania thin film samples or corresponding titanium dioxide powders were characterized by X-ray diffraction, cross-section transmission electron microscopy, nitrogen adsorption, ellipsometery, UV/vis spectrometry, and other techniques to understand the interplay between mesoporosity and optical properties.     

Preparation and Photochromic Behavior of Ormosil Containing Encapsulated AgTCNQ Molecules

Preparation and photochromic behavior of ormosil containing encapsulated AgTCNQ molecules were studied in this paper. The ormosil resulted from hydrolysis and polycondensation of glycidoxypropyltrimethoxysilane, dimethyldimethoxysilane and methyltrimethoxysilane. The time to add AgNO₃ water solution into the resultant sol was a key factor to synthesize AgTCNQ molecules inside ormosil matrix. AgTCNQ molecules encapsulated in the ormosil showed different photochromic behavior compared with pure AgTCNQ film: normal photochromic reaction can be realized, while reverse photochromic reaction can not. The “cage” model was used to explain this phenomenon.     

Experimental and theoretical investigations of cyanide detection using a photochromic naphthopyran

Photochromic naphthopyran derivatives were synthesised for anion recognition applications. The crystal structure, experimental and theoretical investigation of photochromic and anion sensing properties of a simple naphthopyran derivative were investigated. The naphthopyran derivative displayed good fatigue resistance and selective sensing response towards cyanide ions. The mechanism of complex formation was suggested based on NMR studies. Theoretical calculations were performed to understand the experimental results. An excellent correlation between the theoretical and experimental data was observed.     

Spectrokinetic studies on new bi-photochromic molecules containing two naphthopyran entities

A range of new bi-photochromic molecules containing two identical (3a-d) or two distinct naphthopyran units (6a-d), linked through the phenyl substituents located on the sp³ hybridised pyran ring carbon atom, using conjugated and non-conjugated spacers, have been synthesised from bis-propynols and (substituted)naphthols. Study of the spectrokinetic properties of these compounds under near UV-vis continuous irradiation conditions revealed that the two naphthopyran units are stimulated independently leading to open forms with higher colourabilities but without affecting the individual bleaching kinetics. Compared to the individual photochromic components and to model mono-photochromes it was observed that the nature of the bridge has a small effect on the photochromic properties of each system.     

Photoresponsive organic field-effect transistors involving photochromic molecules

In recent years, organic field-effect transistors (OFETs) with high performance and novel multifunctionalities have attracted considerable attention. Meanwhile, featured with reversible photoisomerization and the corresponding variation in color, chemical/physical properties, photochromic molecules have been applied in sensors, photo-switches and memories. Incorporation of photochromic molecules to blend in the device functional layers or to modify the interfaces of OFETs is common way to build photo-transistors. In this review, we focus on the recent advantages on the study of photoresponsive transistors involving one of three typical photochromic compounds spiropyran, diarylethene and azobenzene. Three main strategies are demonstrated in detail. Firstly, photochromic molecules are doped in active layers or combined with semiconductor structure thus forming photoreversible active layers. Secondly, the modification of dielectric layer/active layer interface is mainly carried out by bilayer dielectric. Thirdly, the photo-isomerization of self-assembled monolayer (SAM) on the electrode/active layer interface can reversibly modulate the work functions and charge injection barrier, result in bifunctional OFETs. All in all, the combination of photochromic molecules and OFETs is an efficient way for the fabrication of organic photoelectric devices. Photoresponsive transistors consisted of photochromic molecules are potential candidate for real applications in the future.     

Chromatic and dynamic characteristics of some photochromes in the components of bifunctional photochromic and electro-optical devices

This work is part of a research project whose final aim is to realise prototypes of bifunctional photochromic and electro-optical devices. The photochrome will be incorporated in films composed by nematic liquid crystals dispersed in a polymeric matrix or in fluid monomer emulsions. To choose suitable photochromic components, the behaviour of some compounds (four naphtho-spiro-indolino-oxazines and a nitromethoxy-spiropyran) was investigated in the components of the matrix (liquid crystals and monomers) and compared with that in organic solvents. The colour-forming and colour-bleaching kinetics were determined. The molecules investigated, while maintaining their photochromic behaviour, generally exhibited a better colorability in liquid crystals and monomers, due to decreasing of the bleaching rate. The results of this work indicate that two of the molecules investigated have the prerequisites of colorability, reversibility and durability to be used in the bifunctional devices. Preliminary tests on the behaviour of a prototype of bifunctional film are reported.     

Colour switching with photochromic vinylidene-naphthofurans

A series of novel photochromic vinylidene-naphthofurans with extended conjugation, and a free hydroxyl function, were easily prepared using the Suzuki reaction. After silanization, these dyes were embedded in ormosil matrices affording solid and transparent materials that acquire different colourations (violet, green, bluish), reversibly, when exposed to the UV (Sun) light, for 2?min, at room temperature. The presence of an extra phenyl ring in some positions affects both the λ_max of absorption of the photochromic compounds in the uncoloured closed and open coloured form. After removal of the light source the materials lose progressively their colouration returning to the initial uncoloured state in less than 15?min?at room temperature.     

Stable photochromism and controllable reduction properties of surfactant-encapsulated polyoxometalate/silica hybrid films

In this paper, we present a novel strategy for fabricating polyoxometalate (POM)-based photochromic silica hybrid films. To combine metal nanoparticles (NPs) into the POMs embedded silica matrix, furthermore, we realized the controllable in situ synthesis of metal NPs in the film by utilizing the reduction property of POMs existing in the reduced state. Through electrostatic encapsulation with hydroxyl-terminated surfactants, the POMs with good redox property can be covalently grafted onto a silica matrix by means of a sol-gel approach, and stable silica sol-gel thin films containing surfactant-encapsulated POMs can be obtained. The functional hybrid film exhibits both the transparent and easily processible properties of silica matrix and the stable and reversible photochromism of POMs. In addition, well-dispersed POMs in a hydrophobic microenvironment within the hybrid film can be used as reductants for the in situ synthesis of metal NPs. More significantly, the size and location of NPs can be tuned by controlling the adsorption time of metal ions and mask blocking the surface. The hybrid film containing both POMs and metal NPs with patterned morphology can be obtained, which has potential applications in optical display, memory, catalysis, microelectronic devices and antibacterial materials.     

Rapid decoloration and acidichromism of photochromic 3,3-diaryl-3H-pyrano[3,2-f]quinolines

Pyranoquinoline, with its light-sensitive fragment and coordination node, provides an ideal matrix for the development of multi-functional photochromic compounds. This paper presents the synthesis and photochromic properties of 3,3-diaryl-3H-pyrano[3,2-f]quinoline derivatives QP1-QP8. All exhibited good photochromism under UV light irradiation followed by biexponential kinetic decay in the dark at ambient temperature. Their photochromic processes were reversible, and acidichromism was observed to occur in solution. The fading speeds of QP2 and QP6 were higher than those of their known naphthopyran counterparts, whereas the decoloring speeds of the six other compounds were all over an order of magnitude higher than those of QP2 and QP6. The synthesized pyranoquinolines exhibited very good fatigue resistance both in solution and the solid state. Compared to other pyranoquinolines, the optical densities of QP2 and QP6, i.e., the compounds with 2,4-dimethoxylphenyl and 1-naphthyl, were enhanced dramatically. For all the synthesized pyranoquinolines, a distinct bathochromic shift was observed with increasing solvent polarity. The structure-property relationship of the pyranoquinolines was revealed through the single-crystal X-ray analysis of QP1 and QP7.     

Synthesis and photochromic properties of substituted naphthopyran compounds

A group of 3,3-diaryl-3H-naphtho[2,1-b]pyran compounds with functional substituents at the 5- and 6-positions of the naphthopyran skeleton and the para positions at the 3-aryl moieties were prepared through condensation reactions between 2-naphthol derivatives and 1,1-diarylprop-2-yn-1-ol derivatives. The chemical structures of the compounds were confirmed by NMR and MS. The crystal structure of 3,3-diphenyl-6-morpholino-3H-naphtho[2,1-b]pyran (4b) was determined and the relationship between the pyran substructure and photochromism was discussed. The photochromic properties were studied as well, and decoloration kinetics of colored forms was fitted to the biexponential model. Among these compounds, 4b was considered to be the best one due to the large ΔOD of colored form, which is one of the most important properties used in the photochromic material.     

Structure and photochromic properties of molybdenumphosphoric acid/TiO<Subscript>2</Subscript> composite films

TiO₂ sol-gel composite films with dropping molybdenumphosphoric acid (PMoA) have been prepared by sol-gel method. The structure and constitute of composite thin films were studied with Fourier transforms infrared spectroscopy (FT-IR) atomic force microscopy (AFM), and X-ray diffraction (XRD) patterns, respectively. The photochromic behavior and mechanism of composite thin films were investigated with ultraviolet-visible spectra (UV-vis) and electron spin resonance (ESR). FT-IR results showed that the Keggin geometry of PMoA was still preserved inside PMoA/TiO₂ composite thin films, and a charge transfer bridge was built at the interface of PMoA and TiO₂ through the Mo-O-Ti bond. Surface topography of the composite film showed obvious changes before/after adding PMoA, and the surface topography of composite films showed obvious changes before/after irradiating as well. Composite thin film had reversible photochromic properties. Irradiated with UV light, transparent films changed from colorless to blue and they can bleach completely with ambient air in the dark. ESR results showed that TiO₂ were excitated by UV light to produce electrons, which deoxidized PMoA to produce heteropolyblues. The photochromic process of PMoA/TiO₂ system was carried through electron transfer mechanism.     

Properties of Water Confined in Periodic Mesoporous Organosilicas: Nanoimprinting the Local Structure

The properties of materials confined in porous media are important in scientific and technological aspects. Topology, size, and surface polarity of the pores play a critical role in the confinement effects, however, knowledge regarding the guest–pore interface structure is still lacking. Herein, we show that the molecular mobility of water confined in periodic mesoporous organosilicas (PMOs) is influenced by the polarity of the organic moiety. Multidimensional solid‐state NMR spectroscopy directly probes the spatial arrangement of water inside the pores, showing that water interacts either with only the silicate layer or with both silicate and organic layers depending on the alternating surface polarity. A modulated and a uniform pore filling mode are proposed for different types of PMOs.     

Thermally reversible photochromic behaviour of new naphthopyrans involving an intramolecular [2+2] cyclization reaction

New 4-(2,2-diphenylethenyl)naphthopyrans were synthesized and their photochromic behaviour in solution were studied under continuous UV light irradiation conditions. Although only one coloured photoproduct was expected to be formed, due to the naphthopyran substitution pattern, NMR analysis on degassed UV irradiated solutions, performed at low temperature, showed the formation of different compounds. Among them, the main product is formed through an intramolecular [2+2] cyclization reaction and show thermally reversible photochromic properties.     

Hydrophilic nature and sorption-diffusion properties of nanocomposite hybrid polysulfone films

Hybrid nanocomposite films containing silica (??11.4 wt.%) or titania (??18.8 wt.%) in the polymer matrix were prepared by the sol-gel method using the hydrolytic polycondensation of tetraethoxysilane and tetrabutoxysilane in a THF solution of aromatic polymer, polysulfone (PSF). The influence of the oxide nature and the film composition on the structure, the interaction of the polymer with oxides, hydrophilicity, and sorption-diffusion properties of the hybrid films were studied by FTIR spectroscopy, atomic force microscopy, dynamic light scattering, and a complex of other physicochemical methods. The absence of chemical or intermolecular hydrogen bonds between the polymer and oxide particles in the PSF films was shown. The average size of the oxides (SiO₂, ??20 nm; TiO₂, ??90 nm) in the films and roughness of their surface (??0.2?C0.8 nm) were determined. The introduction of oxides into the polymer matrix increases the hydrophilic properties and the ability of the PSF films to swell in water; the diffusion coefficients of water and permeability of water vapor in the PSF films also increase. Titania also induces a more considerable change in the structure of the polymer matrix and more strongly affects the sorption-diffusion properties of the hybrid films in aqueous solutions of THF. All prepared nanocomposite films PSF/SiO₂ and PSF/TiO₂ are capable of extracting an organic component from aqueous solutions and can be used as sorbents and membrane films for the removal of organic substances from the aqueous medium.     

Structure and photochromic properties of molybdenumphosphoric acid/TiO_2 composite films

TiO_2 sol-gel composite films with dropping molybdenumphosphoric acid(PMoA) have been prepared by sol-gel method.The structure and constitute of composite thin films were studied with Fourier transforms infrared spectroscopy(FT-IR),atomic force microscopy(AFM),and X-ray diffraction(XRD) patterns,respectively.The photochromic behavior and mechanism of composite thin films were inves-tigated with ultraviolet-visible spectra(UV-vis) and electron spin resonance(ESR).FT-IR results showed that the Keggin geometry...