Electro-optic switching of reflection and refraction is experimentally demonstrated in metasurface liquid crystal cell. Negative metasurface is fabricated by focused-ion-beam milling, and twisted ...nematic cells are constructed with complementary double-split ring resonator and V-shape slot antenna metasurface. By application of an external voltage, electro-optic switchings are achieved in reflection and refraction. It has a strong implication for applications in spatial light modulation and wavelength division multiplexer/demultiplexer in a near-IR spectral range.
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•Synthesis, mesomorphic and electrical properties of a thienothiophene derivative are presented.•Charge carrier transport was investigated in bulk, vacuum and solution deposited thin ...films.•Charge carrier transport was studied by temperature-dependent time-of-flight and in field-effect transistors.•The results show the potential of the melt-processing route for the high mobility organic semiconducting layer preparation.
A novel mesogenic 2,5-bis-(5-octylthiophene)-thieno3,2bthiophene (TT) derivative has been synthesized. The fused-ring thiophene, end-capped with two octylthiophenes, exhibits ordered lamellar mesophases which were characterized by polarizing optical microscopy, differential scanning calorimetry and small-angle X-ray diffraction at various temperatures. The charge transport properties were investigated by time-of-flight technique as a function of temperature. On cooling from isotropic phase, a maximum hole mobility value of 0.07cm2V−1s−1 was measured in the highly ordered mesophase of the bulk films. Field-effect transistor experiments on both solution and vacuum deposited thin films have also been performed. The solution-processed films exhibit charge carrier mobilities several orders of magnitude lower than values extracted from bulk time-of-flight curves and from vacuum deposited thin film transistors. This work provides evidence that the melt-processing route is an efficient alternative to commonly used solution-processing for fabrication of charge transporting layers from liquid crystalline semiconductors, with performances comparable to evaporation techniques.
Terahertz (THz) technology has become more widespread due to its diverse range of potential applications, particularly when combined with various functional metamaterials using cutting-edge ...nanotechnology techniques. In this report, we introduce a highly improved THz imaging technology by comparing complementary metamaterials intuitively based on Babinet’s principle. The THz reflectance spectra for the complementary metamaterials exhibit a significant and distinct association with the polarization angle. Four different polarization angles and metamaterial pattern geometries were tested for the reflectance imaging of a target image pattern. Field enhancement on the metamaterial surface was also investigated using finite element simulations to support the experimental results. Optimizing the metamaterial based on the experimental and calculation results led to high image contrast and quality. The proposed label-free imaging platform was then employed to produce clear contrast images for mouse brain tissue and HEK-293 cells, thus highlighting the potential application of this system to real biological samples.
•The optimization of terahertz reflection imaging based on split-ring shape metamaterial.•Sensitive and non-destructive imaging of real mouse brain tissue and HEK-293 cells without labeling.•Simultaneous acquisition of image and optical properties in large-area for real bio-samples.
We investigate spectral responses of two different terahertz (THz) metamaterials of double split ring resonator (DSRR) and the nano slot resonator (NSR) for molecule sensing in low concentration. Two ...different resonant frequencies of DSRR can be controlled by polarization angle of incident THz beam. For comparison of THz optical characteristics, two NSRs were made as showing the same resonant frequencies as DSRR's multimode. The monosaccharide molecules of glucose and galactose were detected by these two types of metamaterials matching the resonant frequencies in various concentration. NSR shows higher sensitivity in very low concentration range rather than DSRR, although the behavior was easily saturated in terms of concentration. In contrast, DSRR can cover more broad concentration range with clear linearity especially under high quality factor mode in polarization of 67.5 degree due to the Fano resonance. THz field enhancement distributions were calculated to investigate sensing performance of both sensing chips in qualitative and quantitative manner.
Charge transfer (CT) is a fundamental and ubiquitous mechanism in biology, physics and chemistry. Here, we evidence that CT dynamics can be altered by multi-layered hyperbolic metamaterial (HMM) ...substrates. Taking triphenylene:perylene diimide dyad supramolecular self-assemblies as a model system, we reveal longer-lived CT states in the presence of HMM structures, with both charge separation and recombination characteristic times increased by factors of 2.4 and 1.7-that is, relative variations of 140 and 73%, respectively. To rationalize these experimental results in terms of driving force, we successfully introduce image dipole interactions in Marcus theory. The non-local effect herein demonstrated is directly linked to the number of metal-dielectric pairs, can be formalized in the dielectric permittivity, and is presented as a solid analogue to local solvent polarity effects. This model and extra PH3T:PC60BM results show the generality of this non-local phenomenon and that a wide range of kinetic tailoring opportunities can arise from substrate engineering. This work paves the way toward the design of artificial substrates to control CT dynamics of interest for applications in optoelectronics and chemistry.
The cover image shows organic semiconductor materials for near‐infrared lasers, referring to article number 2001947 by Masashi Mamada, Anthony D'Aléo, Chihaya Adachi and co‐workers. Based on their ...core structure, the complete organic emitters are classified as curcuminoids, which are analogues of the curcumin dye found in turmeric. Rational modification of the chemical structure enables bright near‐infrared emission and lasing as well as thermally activated delayed fluorescence. The work represents a promising approach for developing materials for near‐infrared organic electronic devices.
Organic lasing dyes possessing small energy gaps commonly suffer from high thresholds, because of energy-gap law, which induces detrimental nonradiative relaxation. Herein, molecules based on ...alternating donor (D) and acceptor (A) moieties are described. Those linear molecules are built with a spacer between D and A, with a general formula of D–spacer–A–spacer–D. Such modification of the A core allows one to obtain color-tunable lasing properties from yellow to near-infrared (NIR). Into more details, triphenylamine (TPA) is selected as the D moiety, while benzothiadiazole (BTD) and benzo1,2-c:4,5c′bis1,2,5thiadiazole (BBTD) with strong electron-withdrawing capability, are chosen as A cores for yellow ((TPA-F)2BTD) and NIR ((TPA-F)2BBTD) lasing dyes, respectively. Both dyes exhibit high photoluminescence quantum yields (PLQYs) and fast fluorescence radiative rate. The corresponding amplified spontaneous emission (ASE) thresholds of yellow and NIR dyes are as low as 0.5 and 3.8 μJ cm–2 in the solution-processing blending films, with wavelength peaks at 550 and 811 nm, respectively. In those dyes, the long alkyl chains appended on the fluorene conjugated spacer guarantee the high solubility and prevent aggregation. Consequently, for (TPA-F)2BTD, the neat film allows one to reach PLQYs as high as 90%, with a low ASE threshold (1.9 μJ cm–2) and good stability. Therefore, such promising molecular design allows the realization of color-tunable ASE or lasing dyes with very low thresholds.
Controlling photoinduced intramolecular charge transfer at the molecular scale is key to the development of molecular devices for nanooptoelectronics. Here, we describe the design, synthesis, ...electronic characterization, and photophysical properties of two electron donor–acceptor molecular systems that consist of tolane and BF2-containing curcuminoid chromophoric subunits connected in a T-shaped arrangement. The two π-conjugated segments intersect at the electron acceptor dioxaborine core. From steady-state electronic absorption and fluorescence emission, we find that the photophysics of the dialkylamino-substituted analogue is governed by the occurrence of two closely lying excited states. From DFT calculations, we show that excitation in either of these two states results in a distinct shift of the electron density, whether it occurs along the curcuminoid or tolane moiety. Femtosecond transient absorption spectroscopy confirmed these findings. As a consequence, the nature of the emitting state and the photophysical properties are strongly dependent on solvent polarity. Moreover, these characteristics can also be switched by protonation or complexation at the nitrogen atom of the amino group. These features set new approaches toward the construction of a three-terminal molecular system in which the lateral branch would transduce a change of electronic state and ultimately control charge transport in a molecular-scale device.
Fine-structured polymerized cholesteric liquid crystal (PCLC) wedge laser devices have been realized, with high fine spatial tunability of the lasing wavelength. With resolution less than 0.3 nm in a ...broad spectral range, more than one hundred laser lines could be obtained in a PCLC cell without extra devices. For practical device application, we studied the stability of the device in detail over time, and in response to strong external light sources, and thermal perturbation. The PCLC wedge cells had good temporal stability for 1 year and showed good stability for strong perturbations, with the lasing wavelength shifting less than 1 nm, while the laser peak intensities decreased by up to 34%, and the high energy band edge of the photonic band gap (PBG) was red shifted 3 nm by temperature perturbation. However, when we consider the entire lasing spectrum for the PCLC cell, the 1-nm wavelength shift may not matter. Although the laser peak intensities were decreased by up to 34% in total for all of the perturbation cases, the remaining 34% laser peak intensity is considerable extent to make use. This good stability of the PCLC laser device is due to the polymerization of the CLC by UV curing. This study will be helpful for practical CLC laser device development.
We investigated the influence of metal coating on the optical characteristics of Si nanopillar (NP) arrays with and without thin metal layers coated on the sample surface. The reflection dips of the ...metal-coated arrays were much broader and more pronounced than those of the bare arrays. The coated metal layers consisted of two parts—the metal disks on the Si NP top and the holey metal backreflectors on the Si substrate. The Mie-like geometrical resonance in the NPs, the localized surface plasmons in the metal disks, and the propagation of surface plasmon polariton along the backreflector/substrate interface could contribute to the reflection spectra. Finite-difference time-domain simulation results showed that the interplay of the plasmonic effects and the geometric resonance gave rise to significantly enhanced light confinement and consequent local absorption in the metal-Si hybrid nanostructures.
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