Photochromic Films Research Articles

Quantum computation with photochromic films in a Mach–Zehnder interferometer

Photochromic materials are of great interest because they enable the fabrication of photo-activated switches. In this study, an experiment is proposed in which two chromene-based photochromic layers were inserted into the arms of a Mach–Zehnder interferometer. The chromene was studied from the perspective of optical absorption to determine the wavelength-dependent complex refractive index. Impinging ultraviolet light on one of the chromene layers induces a transition from the closed to the open form of the chromene, resulting in different phase shifts in the two arms of the interferometer. This results in a change in the probability of detecting a photon by the two detectors after the second mirror of the Mach–Zehnder interferometer. The experiment may be of interest to researchers working in the fields of quantum information and quantum communications.

Acceleration Photochromic Performance in Tungsten Oxide

Tungsten oxide (WO3) photochromic films require external force to accelerate the return to their original state after being photoinduced to color under ultraviolet light; otherwise, the fading process is exceedingly slow. The research explores the effects of various metal ion dopants on WO3 photochromic performance, with a focus on Fe doping. Fe-WO3 composite films demonstrate rapid coloration (3 minutes) and bleaching (30 minutes) processes, significantly improving upon undoped WO3. The mechanism of Fe ion catalysis in electron transfer is elucidated through HRTEM, SEM, EDS, and XPS analyses. The practical application of Fe-WO3 composite films in smart windows is evaluated using Energy-plus software, showing substantial energy savings across diverse climate zones. Our findings render great opportunities for innovative photochromic designs that can help achieve energy-saving performance in windows.

Multi-Stimuli Responsive Viologen-Imprinted Polyvinyl Alcohol and Tricarboxy Cellulose Nanocomposite Hydrogels.

Photochromic inks have shown disadvantages, such as poor durability and high cost. Self-healable hydrogels have shown photostability and durability. Herein, a viologen-based covalent polymer was printed onto a paper surface toward the development of a multi-stimuli responsive chromogenic sheet with thermochromic, photochromic, and vapochromic properties. Viologen polymer was created by polymerizing a dialdehyde-based viologen with a hydroxyl-bearing dihydrazide in an acidic aqueous medium. The viologen polymer was well immobilized as a colorimetric agent into a polyvinyl alcohol (PVA)/tricarboxy cellulose (TCC)-based self-healable hydrogel. The viologen/hydrogel nanocomposite films were applied onto a paper surface. The coloration measurements showed that when exposed to ultraviolet light, the orange layer printed on the paper surface switched to green. The photochromic film was used to develop anti-counterfeiting prints using the organic hydrogel composed of a PVA/TCC composite and a viologen polymer. Reversible photochromism with strong photostability was observed when the printed papers were exposed to UV irradiation. A detection limit was monitored in the range of 0.5-300 ppm for NH3(aq). The exposure to heat (70 °C) was found to reversibly initiate a colorimetric change.

Solar spectral response of photochromic YHO films

Photochromic yttrium oxyhydride, YHO, has excellent properties as a responsive solar control material, in particular due to its color-neutral darkening. In this work, we have investigated YHO’s spectral response to the solar AM 1.5 spectrum to evaluate how the total photon activation flux changes as a function of thickness and wavelength. The calculations are based on ellipsometry measurements in the 240–2000 nm range. Our results show that the UV light absorption saturates at around 400 nm thick film, while blue light (>400 nm) continues to provide photoactivation well beyond 1 μm thickness. Understanding the spectral response and absorption per unit time of activating photons as a function of material thickness is important for evaluating the material or coating for applications.

Rapid fabrication of polyoxometalate-enhanced photo responsive films from ethyl cellulose (EC) and polyvinylpyrrolidone (PVP)

Ethyl cellulose (EC), polyvinylpyrrolidone (PVP), and phosphomolybdic acid (PMoA) were the components of a new photochromic hybrid film composed of heteropoly acids (abbreviated EC-PVP/PMoA), created by solvent evaporation. The EC-PVP/PMoA mechanism, visible light photochromic behaviors, and microstructure were closely studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), ultraviolet-visible (UV–visible) spectroscopy, X-ray photo electronics (XPS), and Fourier transmission infrared spectroscopy (FTIR). FTIR spectra show that neither the core structures of EC, PVP, nor the Keggin structure of PMoA in the EC-PVP/PMoA composite hybrid film were damaged during fabrication. In the presence of oxygen, the yellowish transparent hybrid film exhibited reversible photochromism and significant photochromic reactivity, becoming blue in the presence of visible light. Upon heating the film at 90 °C for 1 h its photoresponsive properties were enhanced, making the blue color more vibrant and stable due to polyethylene glycol (PEG). The XPS spectra demonstrated a proton transfer procedure during the photochromic process, and the presence of Mo+5 species indicated a photoreduction interaction between the PMoA particles and the EC-PVP matrix. To the best of our knowledge, this is the first EC-PVP combined hybrid film with POMs with promising prospects for solar UV detection and smart glass windows applications.

Characterization and Energy Performance of WO3 Doped and Undoped Photochromic Films

When exposed to light sources, photochromic (PC) materials change their optical properties and can lessen the transmission of UV and infrared radiation. This results in optimal thermal comfort and a pleasing visual contrast between the internal and external settings. This study uses computer modeling to analyze the annual energy usage in a home with natural ventilation in order to compare the effectiveness of photochromic films with commercial glass. The study is carried out using the EnergyPlus program in the cities of São Carlos and Cuiabá ‐ Brazil. Experiments and numerical simulations with data from doped and undoped tungsten trioxide (WO3) PC films are used in the study. Given the rise in energy usage and the pursuit of thermal comfort, this method is essential for assessing the thermal performance of buildings. Evaluations included a comparison of air conditioner performance and energy savings analysis, which leads to a noteworthy annual reduction in energy usage of up to 216.55 kWh and a 40% improvement in visual comfort. It is determined that PC film's dynamic behavior is the best option for comfort in terms of heat, illumination, and visual comfort.

Binder-enhanced reversible photochromic films by tungsten oxide hybrid composites for advanced applications

In this study, we developed binder-enhanced reversible photochromic tungsten oxide (WO3) films for advanced applications. Expanding on previous research, we used tungsten oxide hybrid composites as the base material and incorporated various binders, specifically polyethylene glycol (PEG), polysorbate 80 (PS 80), and carboxymethyl cellulose (CMC), to evaluate their effects on reversible photochromic reactions. Our experiments demonstrated that the inclusion of CMC significantly improved the photochromic properties and exhibited the fastest reversible reactions when compared to PEG and polysorbate 80. This enhancement is attributed to the high density of hydroxyl groups and the network structure of CMC, which facilitate efficient proton transfer and oxygen permeability, both crucial for the reoxidation process in WO3. Density functional theory (DFT) calculations supported these findings by indicating that CMC has a suitable bandgap and electron mobility, which enhance charge injection and transport. Additionally, the fabricated films showed consistent and stable performance under both heat treatment and natural ambient conditions. These results underscore the potential of CMC as an effective binder for developing high-performance, reversible photochromic films suitable for applications in smart windows, displays, and optoelectronic devices.

Photochromic Spiropyran-Based Dual-Emitting Luminescent Hybrid Films for Dynamic Information Anticounterfeiting.

Photoluminescent materials are widely used for information storage and anticounterfeiting, while most of them have the disadvantages of static information performance and weak processability, which is still a challenging task in developing dynamic anticounterfeiting materials with high security levels. Herein, we fabricated a novel photostimuli-responsive dual-emitting luminescent material UPTES-SPn-Tb-hfa, which was obtained by introducing the photochromic molecule spiropyran (SP) and lanthanide complex (Tb-hfa) into a siloxane-polyether matrix using the sol-gel process. Due to the conformation-dependent photochromic fluorescence resonance energy transfer between the Tb-hfa donor and SP acceptor, the ring-closing (SP)/ring-opening (MC) isomerization of the SP unit leads to a reversible luminescence switching in UPTES-SPn-Tb-hfa. This composite material has great potential for advanced anticounterfeiting because of the advantage of rapidly repeatable encryption/decryption for at least 8 times and dynamic luminescent colors within 15 s. In addition, due to its two luminescent centers (Tb3+ and MC), the luminescent color of this material can be regulated by 254 and 365 nm UV-light irradiation, which facilitates the design of multicolored anticounterfeiting labels. Our work presents a novel design methodology to fabricate dynamic anticounterfeiting materials, significantly enhancing the security of anticounterfeiting applications.

Transparent insulating photochromic PU/PTA films for Wide-Spectrum modulated smart windows

Photochromic materials have recently attracted widespread attention in the research of smart windows because they can function without additional devices. In this study, an innovative photochromic thermal insulating hybrid film based on a polyurethane matrix was prepared via a one-pot method, incorporating phosphotungstic acid. The film demonstrates excellent transparency, good mechanical strength, and a significant modulation of the solar spectrum, transitioning from colorless to dark blue under sunlight without the need for additional electron donors. This photochromic behavior is reversible and reproducible without degradation, resulting in a transmittance variation of up to 71 % at 550 nm, which is the most sensitive to the human eye, and more than 50 % modulating performance in 1800 ∼ 2500 nm. In addition, thermal insulation experiments proved that the smart window device prepared by the film could achieve a reduction of 9.3 °C under daylight. Overall, the photochromic films prepared using the one-pot method show good performance involving mechanical strength, efficient photochromic response, broad spectral range modulation, high coloring efficiency and cycling stability, and have promising applications in energy-saving buildings, anti-counterfeiting and smart displays.

Solar responsive building glazing: Experimental analysis of the impact of photochromic glazing on indoor thermal and luminous conditions

The application of films on conventional glazing aims at increasing the glazing performance by reducing energy needs and increasing indoor comfort. Photochromic films in particular can alter their optical properties due to a chromatic change in response to solar radiation, allowing for reduced glare levels and solar heat gains. However, despite the potential of application, this refurbishment solution is still poorly explored. Therefore, the main purpose of this work was to experimentally evaluate the thermal and luminous performance of a double glazing with and without a photochromic film installed, using two office rooms in Lisbon as case study. An extended field experimental campaign was conducted simultaneously in both offices, where temperature, solar radiation and illuminance levels were collected. The key contribution and novelty of this research lies on the experimental assessment of the thermal and visual comfort conditions with the photochromic film under real-occupancy. Even though the photochromic film significantly increased the surface temperatures of the glazing, the indoor air temperature was not negatively affected, with an increase up to 14 % of working hours with comfortable temperature during the heating period. Illuminance levels on vertical/horizontal plane were reduced by 24/36 % in the presence of the photochromic film, when compared to the clear glazing without film, resulting in an increase of 7 % of working hours with useful illuminance during the heating period, and large areas in the office room with imperceptible daylight glare levels when facing the glazing system. The impact of the film was less noticeable during the cooling period.

Dynamic color‐tunable ultra‐long room temperature phosphorescence polymers with photo‐chromism and water‐stimuli response for multilevel anti‐counterfeiting

AbstractDeveloping dynamic color‐tunable ultra‐long room temperature phosphorescence (URTP) polymers with afterglow of over 1 s, photo‐chromism, and multi‐stimuli response for practical anti‐counterfeiting and information security applications is attractive but very challenging. Herein, by doping multicolor phosphorescence pyridinium bromide L block or viologen‐based photo‐chromic V block into polyvinyl alcohol matrixes, the water‐stimuli‐responsive color‐tunable URTP polymer films with afterglow of up to 8 s and the reversible viologen‐based photochromic polymer films have been developed. More significantly, a series of dynamic color‐tunable URTP polymer films with ultra‐long afterglow of over 6 s, photo‐chromism, and water‐stimuli response have been successfully exploited by integrating L and V blocks into one polymer system. Mechanistic investigations have revealed that their photo‐chromism mainly comes from the photo‐generated viologen free radicals. Furthermore, their dynamic multilevel anti‐counterfeiting applications have been demonstrated. These results pave the way to develop smarter multifunctional URTP materials for anti‐counterfeiting and optical sensing.

Photorewriting, Time-Resolved Encryption, and Unclonable Anticounterfeiting with Artificial Intelligence Authentication via a Reversible Photoswitchable System.

In the fields of photolithographic patterning, optical anticounterfeiting, and information encryption, reversible photochromic materials with solid-state fluorescence are emerging as a potential class of systems. A design strategy for reversible photochromic materials has been proposed and synthesized through the introduction of photoactive thiophene groups into the molecular backbone of aryl vinyls, compounds with unique aggregation-induced emission properties, and solid-state reversible photocontrollable fluorescence and color-changing properties. This work develops novel photochromic inks, films, and cellulose hydrogels for enhancing the security of information encryption and anticounterfeiting technologies. They achieve rapid and reversible color change under ultraviolet light irradiation. Dependent upon the rate of color change, higher levels of time-resolved security can be achieved. This feature is important for enhancing the confidentiality of encrypted information and the reliability of security labels. Color-changing cellulose hydrogels, inks, and films consisting of three photochromic fluorescent molecules have quick photoactivity, great photoreversibility and photostability, and good processability, making them ideal for time-delayed anticounterfeiting and smart encryption. Furthermore, specialized algorithms are used to construct convolutional neural networks, and image analysis is performed on these systems, thus solving the current problem of the time-consuming information decryption process. This artificial intelligence method offers new opportunities for enhanced data encryption.

Improving dispersibility of tungsten oxide particles with organic ligands for photochromic films

Tungsten trioxide (WO3) has been studied as a promising photochromic material due to its favorable properties such as low manufacturing cost, high thermal and photostabilities, and low toxicity. Nevertheless, its practical application has been hindered by a relatively slow bleaching rate compared to other photochromic materials. Furthermore, metal oxide particles such as tungsten oxide face challenges in dispersing within process solvents, leading to difficulties in solution-based film fabrication processes. In this study, we aimed to address this limitation by exploring novel approaches to enhance both the dispersibility of tungsten oxides in processing solvents and their photochromic properties. To achieve this, we synthesized tungsten oxide composites by introducing various organic ligands, including polyvinylpyrrolidone (PVP), oleylamine (OA), hexadecylamine (HDA), and cetyltrimethylammonium bromide (CTAB). Through a comparative analysis, we found that the introduction of organic ligands significantly improved the dispersibility of tungsten oxides in processing solvents, while also enhancing their photochromic properties, including bleaching rate. Notably, the PVP ligand demonstrated superior performance in enhancing the overall properties of tungsten oxide composites. Our findings provide insights into the optimization of tungsten oxide-based photochromic materials for practical applications, offering potential directions for improvement and proposals for enhancing their performance and broadening their utility in various fields.

Visible‐Light Photochromism of Polyoxometallate H4PMo11VO40 Composite Film Based on Polyvinylpyrrolidone with a Fast Response

AbstractThe visible‐light photochromic composite films with a fast response were prepared by entrapping H4PMo11VO40 into polyvinylpyrrolidone (PVP) networks. PMo11V/PVP composite films’ structure and morphology were characterized by IR spectroscopy, XRD and TEM. The skeleton structure of PMo11V and PVP were still remained through IR spectroscopy analysis. The photochromism performance of PMo11V/PVP composite films were analyzed by UV‐vis absorption. The photochromic process showed a first‐order kinetics. Meanwhile, the mechanism of photochromism composite films was investigated by XPS. PMo11V/PVP composite films with excellent circulation ability of rising‐fading color which has good application potential.

Memory effect in photochromic rare-earth oxyhydride thin films studied by in situ positron annihilation spectroscopy upon photodarkening-bleaching cycling

Memory effect in photochromic rare-earth oxyhydride thin films studied by <i>in situ</i> positron annihilation spectroscopy upon photodarkening-bleaching cycling

Reversible Photochromism for Dynamically Tuning Full‐Color Circularly Polarized Luminescence Toward Multi‐Level Anti‐Counterfeiting Application

AbstractPhotochromic circularly polarized luminescence (CPL) demonstrates broad application prospects in the field of advanced functional materials. However, the current photochromic CPL focuses predominantly on single‐band CPL adjustment, and how to achieve dynamically tunable CPL in multi‐band is still highly challenging. This work reports the success in utilizing reversible photochromism for realizing full‐color CPL emission. Photochromic flexible films are created consisting of triple components: spiropyran (SP) working as photochromic matter, polyurethane (PU) as matrix, and chiral helical polyacetylene as chiral component. Further introducing blue fluorophore 9‐anthracene carboxylic acid (ACA) in the film, blue CPL and red CPL are emitted respectively through selective absorption/transmission and circularly polarized fluorescence energy transfer (CPF‐ET). Doping the photochromic film with diverse fluorophores provides full‐color CPL emission. Adding Zn2+ further intensifies fluorescence and CPL via forming merocyanine (MC)‐Zn2+ complex. Taking advantage of the diverse fluorescence and CPL emission, anti‐counterfeiting, and secondary encryption application of the resulting photochromic CPL materials are demonstrated.

Photochromic Thermoelectric Smart Window for Season‐Adaptive Solar Heat and Daylight Management

AbstractPhotochromic smart windows have drawn increasing attention as an approach to improve building energy efficiency and enhance indoor daylight comfort. However, existing photochromic smart windows still block sunlight from entering the room on sunny winter days, causing additional energy consumption for heating. Herein, a dual‐mode smart window is designed with decoupled photo and thermal functions by combining colorless Fe‐doped WO3 photochromic film with window rotation. Based on this, selective heating and cooling of the room between winter and summer is achieved while maintaining the daylight comfort benefits during all seasons. As a proof of concept, the smart window reduces the temperature of a model house by up to 7.9 °C in summer mode, while in winter mode the temperature is only reduced by 0.7 °C. The proposed seasonally adaptive dual‐mode smart window obtains by window rotation overcomes the limitations of conventional photochromic smart windows, which not only achieves better energy efficiency but also retains improved daylight comfort. Furthermore, it demonstrates that the heat absorbed by the smart window can be harnessed to produce electricity through the integration of thermoelectric modules within the glazing, which enhances its impact on reducing energy consumption.

Robust, Ultrafast and Reversible Photoswitching in Bulk Polymers Enabled by Octupolar Molecule Design

AbstractImproving the photoswitching rate and robustness of photochromic molecules in bulk solids is paramount for practical applications but remains an on‐going challenge. Here, we introduce an octupolar design paradigm to develop a new family of visible light organic photoswitches, namely multi‐branched octupolar Stenhouse Adducts (MOPSAs) featuring a C3‐symmetrical A3‐(D‐core) architecture with a dipolar donor–acceptor (D–A) photochrome in each branch. Our design couples multi‐dimensional geometric and electronic effects of MOPSAs to enable robust ultrafast reversible photoswitching in bulk polymers. Specifically, the optimal MOPSA (4 wt %) in commercial polyurethane films accomplishes nearly 100 % discoloration in 6 s under visible light with ∼ 100 % thermal‐recovery in 17.4 s at 60 °C, while the acquired kinetics constants are 3∼7 times that of dipolar DASA counterpart and 1∼2 orders of magnitude higher than those of reported DASAs in polymers. Importantly, the MOPSA‐doped polymer films sustain 500 discoloration/recovery cycles with slow degradation, superior to the existing DASAs in polymers (≤30 cycles). We discover that multi‐dipolar coupling in MOPSA enables enhanced polarization and electron delocalization, promoting the rate‐determining thermal cyclization, while the branched and non‐planar geometry of MOPSA induces large free volume to facilitate the isomerization. This design can be extended to develop spiropyran or azobenzene‐based ultrafast photochromic films. The superior photoswitching performance of MOPSAs together with their high‐yield and scalable synthesis and facile film processing inspires us to explore their versatile uses as smart inks or labels for time‐temperature indicators, optical logic encryption and multi‐levelled data encryption.

Robust, Ultrafast and Reversible Photoswitching in Bulk Polymers Enabled by Octupolar Molecule Design.

Improving the photoswitching rate and robustness of photochromic molecules in bulk solids is paramount for practical applications but remains an on-going challenge. Here, we introduce an octupolar design paradigm to develop a new family of visible light organic photoswitches, namely multi-branched octupolar Stenhouse Adducts (MOPSAs) featuring a C3-symmetrical A3-(D-core) architecture with a dipolar donor-acceptor (D-A) photochrome in each branch. Our design couples multi-dimensional geometric and electronic effects of MOPSAs to enable robust ultrafast reversible photoswitching in bulk polymers. Specifically, the optimal MOPSA (4 wt %) in commercial polyurethane films accomplishes nearly 100 % discoloration in 6 s under visible light with ∼ 100 % thermal-recovery in 17.4 s at 60 °C, while the acquired kinetics constants are 3∼7 times that of dipolar DASA counterpart and 1∼2 orders of magnitude higher than those of reported DASAs in polymers. Importantly, the MOPSA-doped polymer films sustain 500 discoloration/recovery cycles with slow degradation, superior to the existing DASAs in polymers (≤30 cycles). We discover that multi-dipolar coupling in MOPSA enables enhanced polarization and electron delocalization, promoting the rate-determining thermal cyclization, while the branched and non-planar geometry of MOPSA induces large free volume to facilitate the isomerization. This design can be extended to develop spiropyran or azobenzene-based ultrafast photochromic films. The superior photoswitching performance of MOPSAs together with their high-yield and scalable synthesis and facile film processing inspires us to explore their versatile uses as smart inks or labels for time-temperature indicators, optical logic encryption and multi-levelled data encryption.

Chemical state and atomic structure in stoichiovariants photochromic oxidized yttrium hydride thin films

Abstract We investigate the effective oxidation state and local environment of yttrium in photochromic YHO thin film structures produced by e-beam evaporation, along with their chemical structure and optical properties. Transmission electron microscopy images reveal the oxidized yttrium hydride thin film sample exhibiting a three-layered structure. X-ray photoelectron spectroscopy (XPS) measurements manifest that the oxidation state of yttrium is modified, dependent on the film’s composition/depth. Furthermore, Ion beam analysis confirms that this variability is associated with a composition gradient within the film. X-ray absorption spectroscopy at the Y K-edge reveals that the effective oxidation state of yttrium is approximately +2.5 in the transparent/bleached state of YHO. Spectroscopic ellipsometry investigations showed a complex non-linear optical depth profile of the related sample confirming the dominant phase of YHO and the presence of Y2O3 and Y towards the middle of the film. The first evidence of (n; k) dispersion curves for e-beam sputtered photochromic YHO thin films are reported for transparent and dark states.