High-contrast Switching Research Articles

Construction of a tetraphenylethene derivative exhibiting high contrast and multicolored emission switching

Emission of a tetraphenylethene derivative with low symmetry can be switched among three different states with high contrast by external stimuli.

Long-range surface-plasmon-enhanced all-optical switching and beam steering through nonlinear Kerr effect

A proposition toward all-optical tuning of long-range surface-plasmon-enhanced beam shifts and all-optical switching is implemented analytically by exploitation of Kerr effect induced refractive index change through varying pump light intensity in a multilayer long-range surface-plasmon configuration at 1550 nm. Through the optimized design comprising polydiacetylene para-toulene sulfonate as a Kerr polymer, a high-contrast all-optical switch with a pump intensity threshold of 0.15 GW/cm2 is proposed. The design also provides giant spatial and angular Goos–Hanchen and Imbert–Fedorov shifts at mm and µrad ranges along with wide range of tunability of beam shifts with the varying pump light intensity and the varying incident angle. Moreover, exact beam position and beam steering considering the conjoint effect of spatial and angular Goos–Hanchen and Imbert–Fedorov shifts for different incident polarizations are also obtained. This idea proffers a new possibility for pulse generation, optical sensors applications, optical modulation, geodetic surveying, etc.

High Contrast Electrochromic Polymer and Copolymer Materials Based on Amide-Substituted Poly(Dithienyl Pyrrole)

Conducting polymers have attracted attention as active materials for low power consuming, flexible devices with vivid colors and simple, room temperature processing methods. However, the conductive polymers with high-contrast electrochromic properties are limited in the literature. Here we achieve high-contrast electrochromic switching by copolymerization of newly synthesized an amide substituted dithienyl pyrrole (PBA) and 3,4-ethylenedioxythiophene (EDOT). In order to obtain the best optical properties of copolymer, spectral characteristics of the synthesized copolymers with different monomer feed ratios were investigated. Both homopolymer and copolymer films exhibit well defined redox and satisfied coloration efficiency. Spectroelectrochemistry studies indicate that the P(PBA-co-EDOT) has a lower bandgap (1.67 eV) and shows the excellent optical contrast (77% of 1000 nm) and coloration efficiency (697.01 cm2 C−1). The copolymer method provides a novel way to fabricate a freestanding organic electrochromic device. Additionally, the fluorescence properties of both monomer and polymer were investigated. P(PBA) having strong emission and good solubility and also P(PBA) has the potential to be used in OLEDs.

High contrast switching of transmission due to electrohydrodynamic effect in stacked thin systems of liquid crystals.

We study the opportunity of using electrohydrodynamic instabilities in a nematic liquid crystal mixture with negative dielectric anisotropy for controlling laser beams. Switching between naturally transparent and diffuse light scattering states is achieved by application of low frequency, low amplitude voltages. The specifics of diffuse light scattering state depending on the orientation and thickness of the liquid crystal layer are revealed. The switching occurs on a milliseconds time scale. Combination of thin, flexible liquid crystal cells allows polarization independent, high contrast, fast switching in a broad band of visible wavelengths.

Electroswitchable Emission and Coloration Based on Single-Molecular Fluoran Derivatives

Multifunctional molecular switches exhibiting changes in both emission and coloration in response to various external triggers such as thermal, photo, and electric stimuli have attracted much attention for potential application as chemical sensors, biochemical labels, molecular logic gates, molecular memories, and display devices. In this study, we demonstrated reversible electrochemically induced high-contrast switching of the emission and coloration of fluoran molecules associated with changes in the intramolecular structure. In order to investigate changes in the photophysical properties induced by electrical stimuli, we measured cyclic voltammogram, absorption spetra, emission spectra, and molecular orbital calculation. The mechanism for this electroswitching was attributed to the reversible electrochemically induced closing and opening of the lactone ring in the fluoran molecule. All neutral fluoran molecules were colorless and did not exhibit any fluorescence, while the oxidized (lactone ring-opened form) molecule was yellow and displayed a green fluorescence as a consequence of the extended, planar, conjugated system. Furthermore, this fluoran molecule achieved reversible electroswitchable emission and coloration with high on/off contrast[1]. In order to achieve a quick response time and high reversibility of the electroswitching optical device for modulating both emission and coloration, a 1,4-benzoquinone (BQ) molecule was introduced as a bifunctional material. The inclusion of a redox-active moiety on the auxiliary electrode maintained the charge balance and acted as an EC molecule (transparent/yellow in neutral/reduced state, respectively). BQ acted as a bifunctional molecule, leading to quick and stable switching of both emission and coloration[2]. Reference [1] K. Kanazawa, K. Nakamura and N. Kobayashi, J. Phys. Chem. A, 118, 6026–6033 (2014).[2] K. Kanazawa, K. Nakamura and N. Kobayashi, Sol. Ener. Mater. Solar Cell., 145, 42-53 (2016). Figure 1

High-contrast and fast electrochromic switching enabled by plasmonics

With vibrant colours and simple, room-temperature processing methods, electrochromic polymers have attracted attention as active materials for flexible, low-power-consuming devices. However, slow switching speeds in devices realized to date, as well as the complexity of having to combine several distinct polymers to achieve a full-colour gamut, have limited electrochromic materials to niche applications. Here we achieve fast, high-contrast electrochromic switching by significantly enhancing the interaction of light—propagating as deep-subwavelength-confined surface plasmon polaritons through arrays of metallic nanoslits, with an electrochromic polymer—present as an ultra-thin coating on the slit sidewalls. The switchable configuration retains the short temporal charge-diffusion characteristics of thin electrochromic films, while maintaining the high optical contrast associated with thicker electrochromic coatings. We further demonstrate that by controlling the pitch of the nanoslit arrays, it is possible to achieve a full-colour response with high contrast and fast switching speeds, while relying on just one electrochromic polymer.

A novel red to transmissive electrochromic polymer based on phenanthrocarbazole

This work describes the synthesis of a novel red to transmissive electrochromic polymer with high optical contrast and fast switching times.

Directed self-assembly of nematic liquid crystals on chemically patterned surfaces: morphological states and transitions.

The morphology and through-film optical properties of nematic liquid crystals (LCs) confined between two surfaces may be engineered to create switches that respond to external electric fields, thereby enabling applications in optoelectronics that require fast responses and low power. Interfacial properties between the confining surfaces and the LC play a central role in device design and performance. Here we investigate the morphology of LCs confined in hybrid cells with a top surface that exhibits uniform homeotropic anchoring and a bottom surface that is chemically patterned with sub-micron and micron- wide planar anchoring stripes in a background of homeotropic anchoring. In a departure from past work, we first investigate isolated stripes, as opposed to dense periodic arrays of stripes, thereby allowing for an in-depth interpretation of the effects of patterning on LC morphology. We observe three LC morphologies and sharp transitions between them as a function of stripe width in the submicron and micron regimes. Numerical simulations and theory help explain the roles of anchoring energy, elastic deformation, entropy, pattern geometry, and coherence length of the LC in the experimentally observed behavior. The knowledge and models developed from an analysis of results generated on isolated features are then used to design dense patterned substrates for high-contrast and efficient orientational switching of LCs in response to applied fields.

Stimuli-Responsive Reversible Fluorescence Switching in a Crystalline Donor-Acceptor Mixture Film: Mixed Stack Charge-Transfer Emission versus Segregated Stack Monomer Emission.

We report on a molecularly tailored 1:1 donor-acceptor (D-A) charge-transfer (CT) cocrystal that manifests strongly red-shifted CT luminescence characteristics, as well as noteworthy reconfigurable self-assembling behaviors. A loosely packed molecular organization is obtained as a consequence of the noncentrosymmetric chemical structure of molecule A1, which gives rise to considerable free volume and weak intermolecular interactions. The stacking features of the CT complex result in an external stimuli-responsive molecular stacking reorganization between the mixed and demixed phases of the D-A pair. Accordingly, high-contrast fluorescence switching (red↔blue) is realized on the basis of the strong alternation of the electronic properties between the mixed and demixed phases. A combination of structural, spectroscopic, and computational studies reveal the underlying mechanism of this stimuli-responsive behavior.

Mechanochromic Luminescence of Aggregation-Induced Emission Luminogens.

Mechanochromic (MC) luminogens have found promising applications in mechanosensors, security papers, and optical storage for their change in emission behaviors in response to mechanical stimuli. Examples on MC luminescent materials are rare before the discovery of MC luminescence in aggregation-induced emission (AIE) luminogens. The twisted conformations of AIE luminogens (AIEgens) with appropriate crystallization capability afford loosely packing patterns, which facilitates their phase transformation in the solid state. The amorphous films of AIEgens exhibit enhanced emission intensity upon pressurization due to the increased molecular interactions, whereas crystals of AIEgens exhibit MC luminescence due to their amorphization by mechanical stimuli. AIEgens enrich the type of MC luminogens but those showing high emission contrast and multicolor emission switching and those working in a turn-on emission mode are seldom reported. Disclosure of the design strategy of high performance MC luminogens and exploration of their high-tech applications may be the future research directions for MC luminogens.

Switching the Localized Surface Plasmon Resonance of Single Gold Nanorods with a Phase-Change Material and the Implementation of a Cellular Automata Algorithm Using a Plasmon Particle Array

We investigate the modulation of the localized surface plasmon resonance (LSPR) of a gold nanorod (AuNR) using a GeSbTe film as an active medium. We demonstrate high-contrast switching of LSPR in an AuNR/GST/Au thin film sandwich structure upon phase change. To go beyond this single-particle switching functionality, we consider a plasmon particle system interacting with a phase-change material (PCM) to discuss the possibility of parallel processing devices with memory functionality, exploiting the plasticity and threshold behavior that are inherent characteristics of PCMs. We demonstrate that the temporal and spatial evolution of a plasmon-PCM array system can be equivalent to a cellular automata algorithm.

Experimental and theoretical investigation of tetra-oxidized terarylenes with high-contrast fluorescence switching

Photochromic tetra-oxidized terarylenes with ethyl-substituents at the reactive carbon atoms are demonstrated as turn-on fluorescent molecules.

Morphology and Emission Tuning in Fluorescent Nanoparticles Based on Phenylenediacetonitrile

Organic nanoparticles exhibiting tunable emission properties in response to morphology changes are attractive for application in low-cost fluorescence sensors, e.g., for sensing vapors, temperature, etc., and therefore, convenient ways for altering nanoparticle morphology are highly desired. In this work, phenylenediacetonitrile-based molecules featuring aggregation-induced emission enhancement which are suitable for the realization of morphology-tunable nanoparticles by precipitation method have been designed. The morphology tuning was enabled by rational functionalization of the molecular backbone with pyrazole moieties and adjacent alkoxy/cyclic side-groups, which were varied in size and branchiness. The longer alkoxy chains generally caused formation of crystalline nanostructures, while shorter ones resulted in preferably amorphous nanoaggregates. Remarkably, the sharp tuning of the nanoparticle morphology (crystalline → amorphous → crystalline) with the subsequent high-contrast emission switching (emissive → nonemissive → emissive) was achieved for phenylenediacetonitrile bearing dihexylmethoxy-type side-groups by adjusting solvent/nonsolvent ratio (1/1 → 1/4 → 1/9) in the mixture with the dissolved compound. Electron and polarized optical microscopy data confirmed the intermediate nonemissive state (ΦF = 2%) emanates from amorphous spherical aggregates, whereas two highly emissive states (ΦF up to 70%) originate from nanowire-like crystalline particles, which were attributed to different phenylenediacetonitrile polymorphs. Finally, the applicability of the phenylenediacetonitrile-based fluorescent nanoparticles for organic vapor sensing was demonstrated.

MEMS reconfigurable metamaterial for terahertz switchable filter and modulator.

We demonstrate a reconfigurable metamaterial developed by surface micromachining technique on a low loss quartz substrate for a tunable terahertz filter application. The device implements a reconfigurable RF-MEMS (radio frequency - micro electro mechanical systems) capacitor within a split-ring resonator (SRR). Time-domain spectroscopy confirms that the tunability of the SRR resonance and thus the terahertz transmittance are electrostatically controlled by the RF-MEMS capacitor. Due to the high transparency and low loss of quartz used as a substrate, the device exhibits a high contrast switching performance of 16.5 dB at 480 GHz, which is also supported by the terahertz dynamic modulation measurement results. The device shows promise for tunable transmission terahertz optics.

High-Contrast All-Optical Controllable Switching and Routing in Nonlinear Photonic Crystals

We present a new high-contrast all-optical controllable switch and router, which is based on two cross-waveguide-based nonlinear photonic crystal switches and a T-branch waveguide. We show that by applying a proper state of control signals (a controlled switching mechanism), the input power can be routed to any of the two output ports. The operation of the proposed device is investigated through the use of analytical and numerical methods.

Design and Syntheses of Electron-Transfer Photochromic Metal–Organic Complexes Using Nonphotochromic Ligands: A Model Compound and the Roles of Its Ligands

The model compound [Zn(HCOO)2(4,4'-bipy)] (1; 4,4'-bipy = 4,4'-bipyridine) is selected in this work to demonstrate the effectiveness of our previously proposed design strategy for electron-transfer photochromic metal-organic complexes. The electron-transfer photochromic behavior of 1 has been discovered for the first time. Experimental and theoretical data illustrate that the photochromism of 1 can be attributed to the electron transfer from formato to 4,4'-bipy and the formation of a radical photoproduct. The electron transfer prefers to occur between formato and 4,4'-bipy, which are combined directly by the Zn(II) atoms. A high-contrast (up to 8.3 times) photoluminescence switch occurs during the photochromic process. The similarity of photochromic behaviors among 1 and its analogues as well as viologen compounds has also been found. Photochromic studies of this model compound indicate that new electron-transfer photochromic metal-organic complexes can be largely designed and synthesized by the rational assembly of nonphotochromic electron-donating and electron-accepting ligands.

Ultralow-energy and high-contrast all-optical switch involving Fano resonance based on coupled photonic crystal nanocavities

We experimentally and theoretically clarified that a Fano resonant system based on a coupled optical cavity has better performance when used as an all-optical switch than a single cavity in terms of switching energy, contrast, and operation bandwidth. We successfully fabricated a Fano system consisting of doubly coupled photonic-crystal (PhC) nanocavities, and demonstrated all-optical switching for the first time. A steep asymmetric transmission spectrum was clearly observed, thereby enabling a low-energy and high-contrast switching operation. We achieved the switching with a pump energy of a few fJ, a contrast of more than 10 dB, and an 18 ps switching time window. These levels of performance are actually better than those for Lorentzian resonance in a single cavity. We also theoretically investigated the achievable performance in a well-designed Fano system, which suggested a high contrast for the switching of more than 20 dB in a fJ energy regime.

All-Optical 2R Regeneration With Contrast Enhancement in a Reflective Vertical Cavity Quantum-Wells Saturable Absorber

Round-trip nonlinear phase-shift of an input signal due to optically induced thermal effects and saturable index change in a low intensity resonant reflective vertical cavity semiconductor (quantum wells) saturable absorber (VCSSA) is investigated theoretically for 2R (re-amplification and re-shaping) regeneration. Calculations are carried out for a high contrast switching system to find the optimum value of parameters such as energy time filling factor (FF) of the input pump signal, top mirror reflectivity (Rt) of the Fabry-Perot cavity and wavelength detuning from the low intensity resonant wavelength of the Fabry-Perot cavity. It is observed that the optimum contrasts are almost the same for a wavelength tuning range as large as 8 nm around the low intensity resonance wavelength of the InGaAs/InP quantum-wells-based VCSSA with Rt of 0.72 and FF of 0.10. The simulation shows that the required average input power is minimal for high contrast 2R regeneration when operated in the short wavelength side.

An electromechanically reconfigurable plasmonic metamaterial operating in the near-infrared

Current efforts in metamaterials research focus on attaining dynamic functionalities such as tunability, switching and modulation of electromagnetic waves. To this end, various approaches have emerged, including embedded varactors, phase-change media, the use of liquid crystals, electrical modulation with graphene and superconductors, and carrier injection or depletion in semiconductor substrates. However, tuning, switching and modulating metamaterial properties in the visible and near-infrared range remain major technological challenges: indeed, the existing microelectromechanical solutions used for the sub-terahertz and terahertz regimes cannot be shrunk by two to three orders of magnitude to enter the optical spectral range. Here, we develop a new type of metamaterial operating in the optical part of the spectrum that is three orders of magnitude faster than previously reported electrically reconfigurable metamaterials. The metamaterial is actuated by electrostatic forces arising from the application of only a few volts to its nanoscale building blocks-the plasmonic metamolecules-that are supported by pairs of parallel strings cut from a flexible silicon nitride membrane of nanoscale thickness. These strings, of picogram mass, can be driven synchronously to megahertz frequencies to electromechanically reconfigure the metamolecules and dramatically change the transmission and reflection spectra of the metamaterial. The metamaterial's colossal electro-optical response (on the order of 10(-5)-10(-6) m V(-1)) allows for either fast continuous tuning of its optical properties (up to 8% optical signal modulation at up to megahertz rates) or high-contrast irreversible switching in a device only 100 nm thick, without the need for external polarizers and analysers.

Unique Piezochromic Fluorescence Behavior of Dicyanodistyrylbenzene Based Donor–Acceptor–Donor Triad: Mechanically Controlled Photo‐Induced Electron Transfer (eT) in Molecular Assemblies

A novel donor-acceptor-donor triad that exhibits fluorescence on-off switching with high contrast ratio (ca. 10(3) ) in response to a mechanical stimulus in the solid state is reported. This system provides a very unique example of high-contrast fluorescence switching that is driven by a mechanical-force-controlled photo-induced electron transfer (eT) in molecular assemblies.