Photochromic Films Research Articles

Highly transparent photochromic films with a tunable and fast solution-like response

Transparent, tunable and fast-response polymeric photochromic films are obtained through the entrapment of nanodroplets made of oil solutions of photochromic dyes.

Investigation on the coloring and bleaching processes of WO3−x photochromic thin films

WO3−x (oxygen deficient tungsten oxide) thin films and WO3−x/Ta2O5 (tantalum oxide) composite films exhibit a huge photochromic effect with 60% near-infrared transmission modulation.

High response photochromic films based on D-A diarylethenes and their application in holography.

A set of photochromic dithienylethenes bearing amino and nitro groups are synthesised and embedded at high concentrations in a polymer matrix (Cellulose Acetate Butyrate, CAB) to produce films showing a large reversible modulation of the complex refractive index in the Vis-NIR spectral range, thanks to an interesting combination of remarkable response at the molecular level and very high load capability in the chosen matrix. The photochromic derivatives are characterized in solution and in CAB films by means of electronic and vibrational spectroscopy, complemented by DFT calculations. Both the real and imaginary part of the refractive index are determined by spectroscopic ellipsometry. The modulation of the refractive index in the near infrared is in the range 0.02–0.04. These are very large values for such kinds of systems and they are due to a favourable combination of very large solubility of the derivatives in CAB and a high polarisability change. As for the change in transparency in the visible, contrast values larger than 103 are easily achieved. Based on such films, holograms are written and reconstructed with a very high fidelity and efficiency.

Incorporation of indolinospirooxazine on ethylene‐vinyl acetate copolymer to produce a intelligently temperature‐regulated nonwhite cool material

ABSTRACTCool materials that adjust cooling efficiency according to sunlight intensity are needed because people have different needs for cooling at different times. Several colors of commercial microencapsulated photochromic powder were melt blended with ethylene‐vinyl acetate copolymer in a two‐roll mill at 90 °C to prepare the photochromic films of corresponding colors. Pink photochromic films [the organic photochromic compound is indolinospirooxazine (NISO)] were selected to continue the following variable experiment due to its best performance in the indoor cooling test. The pink photochromic films change color as well as transmittance according to the intensity of sunlight, thereby achieving an intelligent cooling effect. A maximum decrease around 10 °C was observed in natural environment when the addition amount of pink photochromic powder reaches 2.0 phr under strong sunlight and all films did not show cooling effect under weak sunlight. This material can be covered on buildings to regulate the indoor temperature. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48887.

Casting and inkjet printable photochromic films based on polymethylmethacrylate – Phosphotungstic acid

The incorporation of polyoxometalates in suitable matrices has been a main effort to produce transparent photochromic materials. Polymeric films based on high transparent polymethylmethacrylate (PMMA) containing phosphotungstic acid (PWA) have been obtained by casting and also by inkjet printing. In this investigation, polymeric PMMA matrix containing PWA were developed in an appropriate ratio of CH2Cl2/THF solvents to provide suitable transparent solution. PMMA/PWA composites obtained by casting were characterized by IR-ATR, Raman, XRD, TG/DTG, UV–Vis. Inkjet printing solution were characterized by surface tension (ST), viscosity and contact angle (CA) on glass substrate and films by optical microscopy. Infrared-ATR and Raman spectroscopies showed that the polyoxometalate structure was preserved in the polymeric matrix and the interaction between them occurred due to electrostatic forces. XRD indicated that PMMA and photochromic films were amorphous and display thermal stability up to 300 °C. Upon the UV irradiation, transparent films become blue and the photobleaching process were performed as a function of the temperature in a presence of air. These high transparent and photosensitive photochromic films present potential application as coating by casting and miniatured devices by inkjet printing.

In-situ composition analysis of photochromic yttrium oxy-hydride thin films under light illumination

In this work, we investigate the chemical composition of a reactively sputtered photochromic YHxOy thin film by non-destructive ion beam-based techniques, i.e., Rutherford Backscattering Spectrometry, Particle-Induced X-Ray Emission, Time-of-Flight/Energy coincidence Elastic Recoil Detection Analysis and Elastic Backscattering Spectrometry. To enhance the accuracy of the analysis, the set of spectra was evaluated in an iterative self-consistent approach. This procedure resulted in high-resolution depth profiles of the chemical composition and revealed a thin oxygen-rich-layer on the surface, which apparently does not act as a self-passivation layer. In the film, the concentration of Y remains practically constant, whereas O replaces H during the oxidation process. In-situ light illumination was performed during the compositional analysis in a high vacuum setup. The results from these measurements demonstrate that, for these samples, the induced reversible photochromism is not linked to any detectable change in the bulk composition of the film and can thus take place even in a vacuum environment.

UV Radiation Cumulative Recording Based on Amorphous TiO2 Nanotubes.

Ultraviolet (UV) photochromism is observed from natural light in amorphous TiO2 nanotube arrays (NTAs) for the first time. Surface color of the NTAs film would change from light yellow to dark brown eventually, either under ultraviolet bulb irradiation or basking under natural sunlight. This photochromism is attributed to the appearance of Ti3+ ions in the TiO2 NTAs after UV illumination. Furthermore, a UV radiation cumulative dosimeter is designed and fabricated, consisting of a photochromic film and a colorimetric card, which convert invisible ultraviolet rays into visible color changes. This device helps people to understand intuitively how much UV radiation has been received in total from surrounding environments, which is of great importance for skin safety and public health.

Synthesis, properties and application in polyvinyl butyral of spirooxazine photochromic compounds

PurposeThe purpose of this paper is to evaluate the effect of antioxidant 2,6-di-tert-butyl-p-methylphenol (BHT) on the thermal stability and fatigue resistance of spirooxazine and then study the properties of photochromic polyvinyl butyral resin (PVB) films.Design/methodology/approachBHT was introduced into the spirooxazine system by blending and covalent bonding. The properties of spirooxazine solutions and photochromic PVB films were studied.FindingsThe thermal stability and fatigue resistance of spirooxazine covalently linked (BHT-SO) or mixed (BHT/SO) with BHT were higher than the system without BHT, and BHT-SO was the better one. But acidic substance would greatly impair the fatigue resistance of spirooxazine. The optimum addition amount of BHT-SO2 to PVB was 2.5 per cent, and the minimum limit was 0.01 per cent. The fading kinetic and fatigue resistance of film were similar to the solution and better. Plasticizer could accelerate the fading rate and strengthen the mechanical properties of photochromic film but had no effect on the fatigue resistance.Research limitations/implicationsSpirooxazine could be grafted onto the PVB chain to make the ring closure fading reaction slower.Practical implicationsIn addition to the wide application prospects of photochromic materials in decoration, optical storage, etc., the photochromic PVB film in the car safety glass can absorb sunlight and turn blue, then fade to colorless when the sunlight disappears, making the interior environment more comfortable.Originality/valueThe introduction of BHT into the spirooxazine system not only exerts its ability to capture free radicals, but its bulky volume also increases the resistance of the ring closure, making the fading process slower.

The dependence of structural, electrical and optical properties on the composition of photochromic yttrium oxyhydride thin films

Thin films of yttrium oxyhydride (YHO) exhibit reversible light-induced resistivity and transmission changes at room temperature and ambient pressure. Establishing how the physical properties of YHO films are influenced by their chemical composition is an important challenge that can open the way toward practical applications. In this work, we have prepared YHO thin films with lateral gradient of oxygen and hydrogen concentrations by reactive magnetron sputtering deposition. This enables us to efficiently investigate the effect of changes in the composition of the films on their structural, electrical and optical properties. The as-deposited YHO film appeared to be black opaque and non-photochromic in the oxygen-poor part of the film, and it changed to yellow transparent and photochromic in the oxygen-rich part of the film. We report a gradual increase in the lattice constant with increasing oxygen content of the film, as revealed by grazing incidence X-ray diffraction measurements. Electrical resistivity measurements unveiled that persistent photoconductivity was strongly enhanced as the oxygen content decreased in the photochromic yellow transparent film. Analysis of the kinetics of the photochromic reaction indicated that the bleaching speed increased with increasing oxygen content in the photodarkened film. Unusual large persistent photochromism was discovered in the same yellow YHO film with lowest oxygen content which lasted for almost 10 days. Moreover, it was shown that the optical constants can be tuned by varying the oxygen content in the photochromic film as well.

Oxyhydride Nature of Rare-Earth-Based Photochromic Thin Films.

Thin films of rare-earth (RE)–oxygen–hydrogen compounds prepared by reactive magnetron sputtering show a unique color-neutral photochromic effect at ambient conditions. While their optical properties have been studied extensively, the understanding of the relationship between photochromism, chemical composition, and structure is limited. Here we establish a ternary RE–O–H composition-phase diagram based on chemical composition analysis by a combination of Rutherford backscattering and elastic recoil detection. The photochromic films are identified as oxyhydrides with a wide composition range described by the formula REOxH3–2x where 0.5 ≤ x ≤ 1.5. We propose an anion-disordered structure model based on the face-centered cubic unit cell where the O2– and H– anions occupy tetrahedral and octahedral interstices. The optical band gap varies continuously with the anion ratio, demonstrating the potential of band gap tuning for reversible optical switching applications.

Gelatin/PVA composited photochromic film for light printing with fast rewritability and long-term storage ability

A photochromic film that could be fast erased and possess long-term preservation ability has been designed, and could be used as rewritable paper.

Layered photochromic films stacked from spiropyran-modified montmorillonite nanosheets.

Two-dimensional (2D) nanosheets are a class of fascinating host material that demonstrates a high specific surface area for the immobilization of functional molecules. Herein, we describe a layered photochromic film using montmorillonite 2D nanosheets immobilized with spiropyran units, which demonstrates a remarkable and reversible photochromic behavior. The synthesis of the layered photochromic film includes the intercalation and exfoliation of montmorillonite powders into 2D nanosheets using a spiropyran-modified surfactant and a subsequent vacuum filtration. The photochromic units of spiropyran-modified quaternary ammonium groups are immobilized on the surface of montmorillonite 2D nanosheets through an electrostatic interaction after exchanging with the native cations in montmorillonite during the intercalation and exfoliation. The photoisomerization of the spiropyran units between closed-ring spiropyran and open-ring merocyanine upon visible/UV irradiation contributes to the photochromic behavior of the layered film. The color contrast between the coloration and decoloration states of photochromic film is optimized by increasing the amount of spiropyran-modified cationic surfactant during the intercalation and exfoliation process. Our layered films with a visual photochromic behavior may promote their applications for optical data storage, optical switching and chemical sensing.

Diarylethene-based conjugated polymer networks for ultrafast photochromic films

Two new diarylethene-based conjugated polymers were synthesized, and their films exhibited ultrafast photochromism properties and excellent fatigue resistance.

A Multifunctional Photochromic Light-Modulating Polymer Film

The results of the authors’ studies on development of a multilayer photochromic sun-protective energy-saving polymer film able of reversibly changing its light transmission depending on the intensity of the activating irradiation and of permanently reflecting thermal radiation were analyzed.

Photomechanical response observed for azobenzene-based photochromic amorphous molecular films fabricated on the surface of agar gel

As a novel photomechanical behavior, structural changes of azobenzene-based photochromic amorphous molecular films fabricated on the surface of soft materials such as agar gel were found upon irradiation with linearly polarized laser beam. The present photomechanical behavior included two-stage processes, striped pattern formation in the direction perpendicular to the polarization direction of the incident beam and subsequent band-like structure formation aligned in the direction parallel to the polarization direction. Both glass-transition temperature of the photochromic materials and the viscosity of the underlying layers were suggested to be important factors for exhibiting the present photomechanical behavior.

Nanoporous-template-modulated azopolymers for enhancing reversible photo-transformation

Recyclable utilization of light energy is essential for current information processing. Photochromic films including azopolymers play a key role in capturing photons, in which many optical manipulations can be achieved. Commonly, inorganic nanoparticles are incorporated into organic azopolymers to increase photo-excitation efficiency and reduce the volume shrinkage rate. However, the aggregation of azopolymers and the uneven distribution of nanoparticles can affect both the material transparency and chemical activity. Reversibility of photo-transformation for such a photochromic system is thus inhibited. Here, a new method is proposed that titania porous films with high optical transparency are used as a nano-template for azopolymer deposition. The results showed that inorganic nanoporous structures not only enhance dye adsorption but also inhibit azopolymer aggregation. In a holographic recording, the diffractive signal is increased 3.6 fold and kept constant for a long time with the support of the TiO2 framework. Based on the property, erasable hologram reconstruction is obtained in the nano-hybrid film by the alternated excitation of coherent lights and single light from a blue laser. This work shows a bright way to inhibit molecule aggregation in solid matrices and contributes to exploit updatable photo-transformation devices.

TiO2 nano-particles based photochromic composite films

Abstract Photochromic TiO 2 -based composite films , with a particle size of 30–40 nm, were prepared using a titanium tetra-isopropoxide and a transparent urethane resin . The transparent films turned blue upon UV irradiation. They were color-saturated in about 20 min, then bleached reaching the initial transparency after two hours in a dark room.

Enhanced Efficiency of Functional Smart Window with Solar Wavelength Conversion Phosphor-Photochromic Hybrid Film.

Here, the high sensitivity and enhanced photochromic efficiency of the hybrid film of solar wavelength conversion phosphor and photochromic film for functional smart window have been achieved by fabricating a double-layered hybrid structure of wavelength conversion phosphor and photochromic film. Y2SiO5:Pr3+ phosphor nanoparticles, which upconvert visible light to UV light, were synthesized by simple hydrothermal method. The synthesized Y2SiO5:Pr3+ nanoparticle was coated as layered structured film on photochromic H3PW12O40 film. The Y2SiO5:Pr3+/H3PW12O40 hybrid film showed an enhanced sensitivity and efficiency of photochromic process with solar light irradiation due to the increased UV portion of solar light through upconversion process of visible light by wavelength conversion phosphor layer. The increased UV portion by upconversion process of Y2SiO5:Pr3+ layer through excited-state absorption and energy transfer upconversion process, contributed to an enhancement of coloration rate of photochromic H3PW12O40 film by 7 times with 50 min of 1 sun irradiation due to fast conversion of W6+ state to W5+ state in H3PW12O40 film with 5 times enhanced photochromic sensitivity compared with pristine photochromic film.

Photoluminescence Properties of Photochromic Yttrium Hydride Films Containing Oxygen

Oxidation of YHx±δ modulates its optical properties by converting it from optically opaque to transparent state to the visible light and electrical properties from metallic conductivity to insulating. The qualitative change of the materials properties are related to oxidation‐induced modulation of electronic properties of the material that will influence the band gap and luminescence properties of the oxygen‐containing yttrium hydride (YHO). This work presents the optical properties, studied by optical spectrophotometry and photoluminescence spectroscopy, of YHO thin films deposited by reactive magnetron sputtering at different H2/Ar flow ratios between 0.18 and 0.28. The indirect and direct band gap of the YHO photochromic films in their clear state is estimated from optical absorption measurements performed at room temperature, and found in the range between 2.5 and 2.6 eV (indirect allowed transition) and between 3.0 and 3.3 eV (direct allowed transition). The study of photoluminescence (PL) properties is performed in the temperature range between 10 and 300 K. The luminescence yield corresponding to the clear state was found to be extremely low in all the YHO films, and it reduced even further once the films darkened under UV‐light exposure. The PL emission at room temperature covers the entire UV and visible range, comprising two broad bands centered at around 2.2 and 3.1 eV. The latter band became fine‐structured at low‐temperatures (10 K), showing a series of distinct PL peaks at energy positions between 2.8 and 3.4 eV which were independent of the H2/Ar flow ratio used during deposition. By the comparison of the PL measurements conducted in vacuum with the ones performed in air, it is possible to conclude that the environment plays an important role in the photochromic properties of YHO. The possible intrinsic and extrinsic origin of the structured PL emission is discussed in terms of excitonic features and/or luminescent surface defects. We report that the main optical transitions of the films deposited at different H pressures did not change by variation of temperature or by UV light‐induced color change.

Analysis of colorimetry using the CIE-L*a*b* system and the photocatalytic activity of photochromic films

This work aims to explain how oxide films are correlated when exposed to UV-A radiation, due to the occurrence of similar phenomena. Thus, thin films of TiO2 and TiO2 doped with H2WO4 or Na2WO4·2H2O were made by spin-coating, heat treated between 650 and 800 °C and evaluated for their optical and photocatalytic properties. The X-ray diffraction technique (XRD) was used to determine the crystalline structure of the films. The photochromism was observed through a spectrophotometer using the CIE-Lab colorimetric method. The analysis of the films photocatalytic behavior was obtained following the photodegradation in 125 ml of methyl orange dye (20 ppm). The results showed that the films presented good photochromic and photocatalytic properties due to the synchronization between the chemical and physical properties of TiO2 and tungsten.