A real-time dynamic holographic material using a fast photochromic molecule

Diaryltriazolium Photoswitch: Reaching a Millisecond Cycloreversion with High Stability and NIR Absorption

The exceptional thermal stability of diarylethene closed isomers enabled many applications but also prevented utilization in photochromic systems that require rapid thermal reversibility. Herein, we report the diaryltriazolium (DAT+ ) photoswitch undergoing thermal cycloreversion within a few milliseconds and absorption of the closed form in the near-infrared region above 900 nm. Click chemistry followed by alkylation offers modular and fast access to the electron-deficient DAT+ scaffold. In addition to excellent fatigue resistance, the introduced charge increases water solubility, rendering this photoswitch an ideal candidate for exploring biological applications.

Unraveling Steric Effects on Ultrafast Bond-Dissociation Processes of Photochromic Radical Complexes

Photochromic reactions of the phenoxyl-imidazolyl radical complex (PIC), which is one of the rate-tunable fast T-type photoswitches, dramatically change by the introduction of bulky substituents around the photochromic units. While these substituents are expected to affect the initial bond dissociation processes, they have not been elucidated yet. Here, we revealed the ultrafast bond dissociation processes of PIC derivatives with different bulky substituents by subpicosecond to nanosecond transient absorption spectroscopy. We revealed that the bulky substituents around the photochromic units decelerate the bond dissociation processes, whereas they largely accelerate the thermal back reactions of the photogenerated open-ring isomer. Moreover, we found clear correlations between the formation kinetics of the open-ring isomer and molecular structural changes. The initial bond-dissociation process dictates the products and the efficiency of photochromic reactions. Therefore, revealing these processes is important not only for fundamental photochemistry but also for optimizing photochromic properties for advanced functional materials.

An ultrahigh-fidelity 3D holographic display using scattering to homogenize the angular spectrum

A three-dimensional (3D) holographic display (3DHD) can preserve all the volumetric information about an object. However, the poor fidelity of 3DHD constrains its applications. Here, we present an ultrahigh-fidelity 3D holographic display that uses scattering for homogenization of angular spectrum. A scattering medium randomizes the incident photons and homogenizes the angular spectrum distribution. The redistributed field is recorded by a photopolymer film with numerous modulation modes and a half-wavelength scale pixel size. We have experimentally improved the contrast of a focal spot to 6 × 106 and tightened its spatial resolution to 0.5 micrometers, respectively ~300 and 4.4 times better than digital approaches. By exploiting the spatial multiplexing ability of the photopolymer and the transmission channel selection capability of the scattering medium, we have realized a dynamic holographic display of 3D spirals consisting of 20 foci across 1 millimeter × 1 millimeter × 26 millimeters with uniform intensity.

Photochromic dinuclear iridium(III) complexes having phenoxyl-imidazolyl radical complex derivatives

We demonstrate that the phenoxyl-imidazolyl radical complex (PIC), which is a rate-tunable fast photoswitch, can be used as a ligand that directly coordinates with iridium (III) ions. The iridium complexes show the characteristic photochromic reactions originating from the PIC moiety, whereas the behaviour of transient species is substantially different from that of the PIC.

Influence of Triptycene Annulation on the Photochromism of Diphenylnaphthopyrans: Entropic Control of Thermal Reversion

Regioisomeric naphthopyrans annulated with triptycene, i. e., Prox-NP and Dist-NP, display divergent photochromic behaviors. While steady-state photolysis of Dist-NP led to a very labile colored intermediate that is not observable at room temperature, Prox-NP yielded a remarkably stable species characterized by X-ray crystallography as the TT isomer of o-quinonoid intermediate (Prox-NPQ) with t_1/2 ca. 0.18 years at 298 K. The kinetic analysis of thermal reversion reveals that the bleaching of Prox-NPQ is entropically controlled; the steric effect due to the rigid triptycene scaffold renders Prox-NP a highly constrained system such that the photogenerated colored o-quinonoid form is more entropically relaxed. This constitutes the first instance of an entropically-controlled thermal reversion for the celebrated class of photochromic naphthopyrans. Based on the response of Prox-NP and its colored intermediate Prox-NPQ to different stimuli, namely, light, heat, and acid, the molecular system can be likened to a logic gate with the 'INHIBIT' function.

Photoinduced movement: how photoirradiation induced the movements of matter

Pioneered by the success on active transport of ions across membranes in 1980 using the regulation of the binding properties of crown ethers with covalently linked photoisomerizable units, extensive studies on the movements by using varied interactions between moving objects and environments have been reported. Photoinduced movements of various objects ranging from molecules, polymers to microscopic particles were discussed from the aspects of the driving for the movements, materials design to achieve the movements and systems design to see and to utilize the movements are summarized in this review.

Photochromic spiro-indoline naphthoxazines and naphthopyrans in dye-sensitized solar cells

Photochromic dyes possess unique properties that can be exploited in different domains, including optics, biomedicine and optoelectronics. Herein, we explore the potential of photochromic spiro-indoline naphthoxazine (SINO) and naphthopyran (NIPS) for application in photovoltaics. We designed and synthesized four new photosensitizers with a donor-pi-acceptor structure embedding SINO and NIPS units as photochromic cores. Their optical, photochromic and acidochromic properties were thoroughly studied to establish structure-properties relationships. Then, after unravelling the possible forms adopted depending on the stimuli, their photovoltaic properties were evaluated in DSSCs. Although the photochromic behavior is not always preserved, we elucidate the interplay between photochromic, acidochromic and photovoltaic properties and we demonstrate that these dyes can act as photosensitizers in DSSCs. We report a maximum power conversion efficiency of 2.7% with a NIPS-based dye, a tenfold improvement in comparison to previous works on similar class of compounds. This work opens new perspectives of developments for SINO and NIPS in optical and photovoltaic devices, and it provides novel research directions to design photochromic materials with improved characteristics.

Multiple aggregates from multiple polymorphs: structural and mechanistic insight into organic dye aggregates

This case study provides evidence for the appearance of multiple aggregation forms of a single organic dye, arising from its packing polymorphs in the solid state. Each aggregate can be spectroscopically matched to one polymorph, acquiring nanoscopic structural information even in the absence of conventional H- or J-type aggregation spectral features. The conversion from one polymorphic aggregate to another supports the action of Ostwald's rule of stages in organic aggregates suspended in solution. Mechanistically, dye molecules from one aggregate dissociate then renucleate the more stable aggregate form, the first demonstration for an aggregation-induced emission-active organic dye.

Stepwise Photochromism of Bis(Imidazole Dimer) Bridged by a Sulfur Atom

We report the development of the stepwise photochromic imidazole dimer bridged by a sulfur atom. The one-photon absorption leads to the generation of the colored biradical species, which rapidly recombines to the initial imidazole dimer following first-order reaction kinetics. The further photochemical reaction of the biradical species produces the long-lived colored species, which shows intermolecular dimerization.

Recent advances in low-power-threshold nonlinear photochromic materials

Incoherent nonlinear photophysical and photochemical processes based on stepwise two-photon absorption (2PA) processes have been recently used in materials science owing to their unique photoresponses beyond one-photon processes and lower power thresholds to induce the processes than those of coherent nonlinear optical processes. Among them, nonlinear photochromic materials have received considerable attention because they exhibit unconventional photoresponses compared with other incoherent nonlinear processes such as low-power-threshold nonlinear photoresponses with unimolecular systems, gated photochemical reactions and oxygen-insensitive nonlinear photoresponses. Nonlinear photochromic materials are important not only for colorimetric materials, but also for emergent materials that can enrich the next-generation society such as dynamic holographic materials, which are promising for three-dimensional displays. In this tutorial review, we introduce low-power-threshold nonlinear photochromic materials using stepwise 2PA processes. First, we explain the fundamental concepts of photochemistry as well as photochromic reactions. We attempt to provide an intuitive understanding of incoherent nonlinear optical processes using these fundamental concepts. Then, we introduce several recent examples and potential applications of nonlinear photochromic materials. This tutorial review is important for understanding the scientific progress related to these fields and provides a simple unified picture of the incoherent nonlinear optical properties of different types of photofunctional materials.

Theoretical design of an absorption hologram-based sensor for dose quantification in daylight photodynamic therapy

Daylight photodynamic therapy (D-PDT) is an effective and almost painless treatment for many skin conditions, where successful treatment relies on daylight activation of a topical photosensitizer. Optimization of D-PDT requires accurate assessment of light dose received. There is a requirement for a small-area sensor that can be placed adjacent to the treatment site to facilitate accurate dose quantification. Here, a novel, to the best of our knowledge, configuration for a D-PDT dose sensor, consisting of a holographic absorption grating fabricated in a photosensitive film, is presented. Theoretical modeling of the sensor's response (i.e., change in grating diffraction efficiency due to change in grating absorption modulation, α₁, on exposure to daylight) was conducted using Kogelnik's coupled-wave theory. The influence of the different grating parameters (initial film absorption, thickness, spatial frequency, and reconstruction wavelength) on the sensor response was examined and revealed that the initial absorption and grating thickness values have a large impact on both the magnitude and rate of the D-PDT sensor response. The optimum design for an absorption grating-based D-PDT sensor is described.

Origin of the Anomalous Temperature Dependence of the Photochromic Reaction of Cu-Doped ZnS Nanocrystals

The temperature dependence of the color fading process of thermally reversible photochromic reactions is one of the most important challenges for their industrial applications. Generally, photochromic reactions of organic molecules have a strong temperature dependence due to the occurrence of large conformational changes during the reactions. In contrast, we recently reported that the photochromic reaction of Cu-doped ZnS nanocrystals (NCs) exhibits a very small temperature dependence around room temperature. However, the mechanism underlying this phenomenon has not been clarified yet. Here, we reveal that the anomalous temperature dependence of Cu-doped ZnS NCs originates from the balance between the temperature dependence of the charge recombination and that of the adsorption/desorption of water molecules on the surface of the NCs, which act as hole acceptors. Exploring temperature-insensitive photochromic reactions is important not only for gaining fundamental insight into nanomaterials but also for developing novel photochromic materials for outdoor applications.

Rational design of photochromic diarylbenzene with both high photoreactivity and fast thermal back reactivity

Utilizing the intramolecular CH–N hydrogen bonding and the bulky substituents at the reactive carbons resulted in the development of photochromic diarylbenzene with both high photoreactivity and fast thermal back reactivity.

Photo-magnetic recording of randomized holographic diffraction patterns in a transparent medium

Reconstructions from computer-generated holograms exhibit spurious duplicate images corresponding to higher diffractive orders, originating from the periodic pixels of a spatial light modulator. We explore the possibility of reducing their visibility by randomization of pixel positions at the stage of displaying of the holograms. Experimental validation is shown on a liquid crystal modulator and also in a promising photo-magnetic transparent cobalt-doped yttrium iron garnet, which exhibits spontaneous randomization of written patterns. Micromirror-driven raster scanning of femtosecond pulses is used for point-by-point rewriting of magnetic domains. Recorded holographic patterns diffract visible light beams in accordance with theory and numerical simulations.

Fast Photochromism of the Imidazole Dimers Bridged by Group 14 Atoms

We developed fast photochromic imidazole dimers bridged by group 14 atoms. These compounds reversibly break the C-N bond to generate the colored open-ring biradical form. The colored form thermally reproduces the initial colorless form in the microsecond time scales. Furthermore, the color of the biradical can be easily controlled by the introduction of two different types of the imidazolyl radicals. These results give attractive insights for the further development of fast photochromic imidazole dimers.

Enhancement of Negative Photochromic Properties of Naphthalene-Bridged Phenoxyl-Imidazolyl Radical Complex

Negative photochromism has increased attention as a light-switch for functional materials. A development of fast photochromic molecules has been also expected because a rapid thermal back reaction within a millisecond time scale is useful for real-time switching. Herein, we synthesized the derivatives of the naphthalene-bridged phenoxyl-imidazolyl radical complex (Np-PIC) showing the negative photochromism to demonstrate the efficient strategy to increase the visible light sensitivity and to control the thermal back reaction rates. The distances of the C-C bond of the transient 2,4'-isomer shows good agreement with the thermodynamic stability, leading to the control of the thermal back reaction rate. We revealed the cyclic voltammetry and the DFT calculations are efficient to predict the characters of the HOMO and LUMO. The introduction of the electron-withdrawing dicyanoquinodimethane group is efficient to induce the photochromic reaction with increased visible-light sensitivity by the expansion of the π-conjugation. The results will give an important insight for the future development of fast-responsive negative photochromic molecules.

Improving photosensitivity without changing thermal reactivity in photochromic diarylbenzenes based on accurate prediction by DFT calculations

1,2-Diarylbenzenes (DABs) have been developed as a new family of fast T-type photochromic switches. However, the molecular design strategy for DABs with desired optical and thermal properties is not established. In this work, we explored the best functional in quantum chemical calculations to predict the properties of DABs. Furthermore, we newly designed and synthesized DABs based on the calculation using the best functional, resulting in the improvement of the photosensitivity in the UV-A region (i.e. a shift of absorption to lower energies and an increase in the absorption coefficient) without changing the thermal back-reaction rate.

Red or Near-Infrared Light Operating Negative Photochromism of a Binaphthyl-Bridged Imidazole Dimer

The development of red or near-infrared light (NIR) switchable photochromic molecules is required for an efficient utilization of sunlight and regulation of biological activities. While the photosensitization of photochromic molecules to red or NIR light has been achieved by a two-photon absorption process, the development of a molecule itself having sensitivity to red or NIR light has been now a challenging study. Herein, we developed an efficient molecular design for realizing red or NIR-light-responsive negative photochromism based on binaphthyl-bridged imidazole dimers. The introduction of electron-donating substituents shows the red shift of the absorption band at the visible-light region because of the contribution of a charge-transfer transition. Especially, the introduction of a di(4-methoxyphenyl)amino group (TPAOMe) and a perylenyl group largely shifts the absorption edge of the stable colored form to 900 nm. In addition, because the absorption band of one of the derivatives substituted with TPAOMe covers the whole visible-light region, the colored form shows a neutral gray color. Upon red (660 nm) or NIR-light (790 nm) irradiation, we observed the negative photochromic reaction from the stable colored form to the metastable colorless form. Therefore, the substituted binaphthyl-bridged imidazole dimers constitute the attractive photoswitches within a biological window.

Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical

Visible-light sensitized photoswitches have been paid particular attention in the fields of life sciences and materials science because long-wavelength light reduces photodegradation, transmits deep inside of matters, and achieves the selective excitation in condensed systems. Among various photoswitch molecules, the phenoxyl-imidazolyl radical complex (PIC) is a recently developed thermally reversible photochromic molecule whose thermal back reaction can be tuned from tens of nanoseconds to tens of seconds by rational design of the molecular structure. While the wide range of tunability of the switching speed of PIC opened up various potential applications, no photosensitivity to visible light limits its applications. In this study, we synthesized a visible-light sensitized PIC derivative conjugated with a benzil unit. Femtosecond transient absorption spectroscopy revealed that the benzil unit acts as a singlet photosensitizer for PIC by the Dexter-type energy transfer. Visible-light sensitized photochromic reactions of PIC are important for expanding the versatility of potential applications to life sciences and materials science.

The Island CGH, a new coding scheme: concept and demonstration

Computer generated holograms (CGHs) are powerful optical elements used in many fields, such as wavefront shaping, quality testing of complex optics, and anti-counterfeiting devices. The Lee algorithm is the most used to generate binary amplitude Fourier holograms. Grayscale CGHs are known to give a higher reconstruction quality than binary holograms, but they usually require a cumbersome production process. A very simple and straightforward method of manufacturing rewritable grayscale CGHs is proposed here by taking advantage of two key components: a digital micro-mirror device (DMDs) and a photochromic plate. An innovative algorithm, named Island algorithm, able to generate grayscale amplitude Fourier CGHs, is reported and compared with the standard Lee approach, based on 9 levels. A crucial advantage lies on the fact that the increase or decrease of the quantification does not affect the spatial resolution. In other words, the new coding leads to a higher spatial resolution (for a given CGH size) and a reconstructed image with an order of magnitude higher contrast with respect to the classical Lee-coded hologram. In order to show the huge potential of our approach, a 201 level Island hologram is designed, produced and reconstructed, pushing the contrast to values higher than10⁴. These results reveal the potential of our process as well as our algorithm for generating programmable grayscale CGHs.

Acceleration of photochromism and negative photochromism by the interactions with mesoporous silicas

The adsorption of merocyanine dye onto mesoporous silicas with varied pore sizes (5.5, 9.4 and 2.2 nm) from the toluene solution of 1,3,3-trimethylindolino-6'-nitrobenzopyrylospiran under UV irradiation was investigated quantitatively. The photoinduced adsorption of merocyanine onto SBA-15 with the pore diameter of 9.4 nm followed the pseudo-second order kinetics and the rate constant was larger than that observed for MCM-41 (pore size of 2.2 nm) owing to the efficient diffusion of merocyanine. The maximum adsorbed amounts of the merocyanine dye was 152 mg g-1 of SBA-15, which corresponded to the sufficiently high concentration of merocyanine in the pores (0.376 mol L-1 of pore). The resulting red-colored hybrids (SBA-15 containing merocyanine) showed decoloration in the solid-state by visible light irradiation (negative photochromism). The conversion was high (about 80% at the photostationary state) under visible light irradiation at room temperature using a solar simulator (100 W). The red color was re-generated by storing the photochemically formed colorless samples in the dark at room temperature. The half-lives of the thermal coloration process were 2.6, 1.9 and 1.3 h for the MCM-41, SBA-15s with the BJH pore sizes of 5.5 and 9.4 nm, respectively. Since the coloration was affected by the diffusion of the molecules in the pores, larger pores provided the efficient molecular diffusion, leading to faster reactions.

Photo- and Electro-Driven Molecular Switching System of Aryl-Bridged Photochromic Radical Complexes

Fast photochromic molecules have received much interest in the potential application as a real-time switching trigger in material and biological chemistry. Pentaarylbiimidazole (PABI) and phenoxyl-imidazolyl radical complex (PIC) are one of the fast photochromic molecules based on imidazolyl radicals. Because the photochromic reaction of these fast photochromic molecules proceeds from the optically forbidden S₁ state, it is difficult to estimate the excitation energy to induce the photochromic reactions by spectroscopic techniques. In this study, we performed the electrochemical measurements for PABI and PIC to investigate the electronic properties and to determine the S₀-S₁ transition energies. In addition, we also revealed that the electrochemical reduction of PABI and PIC generates the radical anion which spontaneously shows the C-N bond breaking reaction to produce the radical species. The initial photochromic dimer is reproduced by the reversible oxidation of the anion species. This characteristic photochromic and electrochromic properties can be applicable to the photowritable electrochromic devices with high spatial resolution.

On-Demand Control of the Photochromic Properties of Naphthopyrans

Photofunctional compounds have emerged as critically important materials for both fundamental studies and industrial applications. Control of the thermal decoloration speed to within several seconds while sustaining satisfactory photochromic colorability is an important challenge for the application of such materials to photochromic lenses and smart windows. Photochromic naphthopyran derivatives are utilized for photochromic lenses because of their high durability and easily controllable colorability. However, the residual color imparted by the long-lived transient species upon ceasing light irradiation remains a hindrance to practical applications. In this study, a strategy is demonstrated for on-demand control of the thermal decoloration speed of the transient colored species of naphthopyran derivatives. The increase in the ring-size of the alkylenedioxy moiety on the naphthopyrans accelerates the thermal back-reaction independently of the maximum-absorption wavelength of the colored isomer, leading to the realization of yellow-, red-, and blue-photochromic naphthopyrans with similar thermal fading speeds. This novel molecular design provides a strategy for the future development of advanced photoresponsive materials.

A volumetric three-dimensional digital light photoactivatable dye display

Volumetric three-dimensional displays offer spatially accurate representations of images with a 360° view, but have been difficult to implement due to complex fabrication requirements. Herein, a chemically enabled volumetric 3D digital light photoactivatable dye display (3D Light PAD) is reported. The operating principle relies on photoactivatable dyes that become reversibly fluorescent upon illumination with ultraviolet light. Proper tuning of kinetics and emission wavelengths enables the generation of a spatial pattern of fluorescent emission at the intersection of two structured light beams. A first-generation 3D Light PAD was fabricated using the photoactivatable dye N-phenyl spirolactam rhodamine B, a commercial picoprojector, an ultraviolet projector and a custom quartz imaging chamber. The system displays a minimum voxel size of 0.68 mm³, 200 μm resolution and good stability over repeated ‘on-off’ cycles. A range of high-resolution 3D images and animations can be projected, setting the foundation for widely accessible volumetric 3D displays.

Despite living in a three-dimensional world, almost all information in our society is conveyed in a two-dimensional format. Here, the authors provide a technique for the generation of spatially accurate and high-resolution three-dimensional images using fluorescent photoswitch chemistry.

Programmable CGH on photochromic plates coded with DMD generated masks

Computer Generated Holograms (CGHs) are used for wavefront shaping and complex optics testing. Present technology allows for recording binary CGHs. We propose a Digital Micro-mirror Device (DMD) as a reconfigurable mask, to record rewritable binary and grayscale CGHs on a photochromic plate. Opaque at rest, this plate becomes transparent when it is illuminated with visible light of suitable wavelength. We have successfully recorded the very first amplitude grayscale CGH, with a contrast greater than 50, which was reconstructed with a high fidelity in shape, intensity, size and location. These results reveal the high potential of this method for generating programmable/rewritable grayscale CGHs, which combine DMDs and photochromic substrates.

Organic Optoelectronic Materials: Mechanisms and Applications

Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjugated polymers are considered, and their applications in organic solar cells, photodetectors, and photorefractive devices are discussed.

Fast Photochromic Molecules toward Realization of Photosynergetic Effects

There has been a growing interest toward the development of advanced photofunctional materials whose photoresponses involve multiple photons and molecules because these materials show the photoresponses which cannot be achieved by a one-photon reaction of a single chromophore. These cooperative interactions of multiple photons and molecules are recently termed as the "photosynergetic" effects, and the understanding and utilization of these effects are becoming important research topics. In this Perspective, we overview the recent progress of the fast T-type photochromic molecules involving the stepwise two-photon absorption processes. Although high power pulse lasers were necessary to induce conventional simultaneous and stepwise two-photon absorption processes, the stepwise two-photon absorption process with the fast photochromic compound can be initiated by extremely weak continuous wave (CW) LEDs. The basic concept and future outlook of the fast photochromism involving the stepwise two-photon absorption process will be discussed.

Fast Negative Photochromism of 1,1'-Binaphthyl-Bridged Phenoxyl-Imidazolyl Radical Complex

Negative photochromism, in which a thermally stable colored form isomerizes to the transient colorless form by light irradiation and the back reaction occurs thermally, is advantageous in its applications for photoswitching materials because visible light can cause the photochromic color change of the materials. Moreover, the photochromic color change can be induced even on the inside of the materials due to the absence of the reabsorption of the visible excitation light by the photogenerated colorless species. While several negative photochromic compounds have been reported, the time scales of the back reaction are still slower than minutes, and no available fast responsive negative photochromic compounds have been reported. Here, we developed a negative photochromic 1,1'-binaphthyl-bridged phenoxyl-imidazolyl radical complex (BN-PIC) which enables fast photoswitching by visible light. The stable colored BN-PIC shows instantaneous decoloration by visible light irradiation, and the photogenerated colorless form thermally reverts to the initial colored form with a half-life of 1.9 s at room temperature. BN-PIC can also cause the drastic change in the chiroptical properties by the photochromic reaction, and the rate of the thermal back reaction is affected by the chirality of the solvent. Since the negative photochromic reaction can occur on the inside of the materials, the fast negative photochromism is expected to have an impact in the fields of photoresponsive materials of solid states and molecular aggregates.

Stealth fast photoswitching of negative photochromic naphthalene-bridged phenoxyl-imidazolyl radical complexes

A novel negative photochromic compound, Np-PIC, shows the fast thermal back reaction in the millisecond time scale.

Thiophene-substituted phenoxyl-imidazolyl radical complexes with high photosensitivity

Fast photoswitch molecules became sensitive to visible light by using a thiophene ring as a radical linker unit.

Nano-sized Ag inserted into ITO films prepared by continuous roll-to-roll sputtering for high-performance, flexible, transparent film heaters

We demonstrate high-performance, flexible, transparent film heaters fabricated on a conductive Ag layer inserted into ITO films prepared by pilot-scale roll-to-roll (RTR) sputtering.

Crystal Violet Lactone Salicylaldehyde Hydrazone Zn(II) Complex: a Reversible Photochromic Material both in Solution and in Solid Matrix

Crystal violet lactone (CVL) is a classic halochromic dye which has been widely used as chromogenic reagent in thermochromic and piezochromic systems. In this work, a very first example of CVL-based reversible photochromic compound was developed, which showed distinct color change upon UV-visible light irradiation both in solution and in solid matrix. Moreover, metal complex of CVL salicylaldehyde hydrozone was facilely synthesized, exhibiting reversible photochromic properties with good fatigue resistance. It was served as promising solid material for photo-patterning.

Photo-control of the thermal radical recombination reaction: photochromism of an azobenzene-bridged imidazole dimer

Among various kinds of photochromic compounds, bridged imidazole dimers have been known as fast photo-switch molecules. Bridged imidazole dimers have opened up various potential applications to photochromic lenses and real-time holographic displays. The optical properties of bridged imidazole dimers strongly depend on the bridging moiety to tether two imidazole rings. Therefore, the control of the bridging structure by introducing another photochromic moiety would increase the versatility of bridged imidazole dimers. In this study, we designed and synthesized a new type of the bridged imidazole dimer 1 which has the azobenzene moiety as the photo-responsive linker. The cis–trans isomerization of the azobenzene moiety enables to change the distance between the photogenerated radical pairs. The two structural isomers, cis–1 and trans–1, are observed and both compounds undergo the photochromism to produce the imidazolyl radicals. We found that the two imidazolyl radicals generated from cis–1 are close enough to form the intramolecular C–N bond, whereas the imidazolyl radicals of trans–1 undergo the intermolecular recombination reaction due to the long distance between the radicals. Our results demonstrate the control of intra-/intermolecular radical recombination reactions by the combination of the two photochromic compounds.

Rational molecular designs for drastic acceleration of the color-fading speed of photochromic naphthopyrans

We report rational molecular designs for acceleration of the color-fading speed of photochromic 3H-naphthopyrans. By using steric and electrostatic repulsions induced by substituents at the 2- and 10-positions of 3H-naphthopyrans, the color-fading speed accelerates from tens of minutes to microsecond time scales. The long-lived residual color, which is an important problem to be solved for industrial applications, can also be suppressed by these strategies.

Thermal response of transparent silver nanowire/PEDOT:PSS film heaters

Thermal response behavior of transparent silver nanowire/PEDOT:PSS film heaters are intensively studied for manipulating heating temperature, response time, and power consumption. Influences of substrate heat capacity, heat transfer coefficient between air and heater, sheet resistance and dimension of Ag nanowire film, on the thermal response are investigated from thermodynamic analysis. Suggestion is given for practical applications that if other parameters are fixed, Ag nanowire coverage can be utilized as an effective parameter to adjust the thermal response. The heat transfer coefficient plays opposite roles on thermal response speed and achievable steady temperature. A value of ≈32 W m(-2) K(-1) is obtained from transient process analysis after correcting it by considering heater resistance variation during heating tests. Guidance of designing heaters with a given response time is provided by forming Ag nanowire film with a suitable sheet resistance on substrate of appropriate material and a certain thickness. Thermal response tests of designed Ag heaters are performed to show higher heating temperature, shorter response time, and lower power consumption (179 °C cm(2) W(-1)) than ITO/FTO heaters, as well as homogeneous temperature distribution and stability for repeated use. Potential applications of the Ag heaters in window defogging, sensing and thermochromism are manifested.

Scanning focused refractive-index microscopy

We present a novel scanning focused refractive-index microscopy (SFRIM) technique to obtain the refractive index (RI) profiles of objects. The method uses a focused laser as the light source, and combines the derivative total reflection method (DTRM), projection magnification, and scanning technique together. SFRIM is able to determine RIs with an accuracy of 0.002, and the central spatial resolution achieved is 1 µm, which is smaller than the size of the focal spot. The results of measurements carried out on cedar oil and a gradient-refractive-index (GRIN) lens agree well with theoretical expectations, verifying the accuracy of SFRIM. Furthermore, using SFRIM, to the best of our knowledge we have extracted for the first time the RI profile of a periodically modulated photosensitive gelatin sample. SFRIM is the first RI profile-resolved reflected light microscopy technique that can be applied to scattering and absorbing samples. SFRIM enables the possibility of performing RI profile measurements in a variety of applications, including optical waveguides, photosensitive materials and devices, photorefractive effect studies, and RI imaging in biomedical fields.