Polarized Light Irradiation Research Articles

Distinctive Chiral Conformations Induced to Poly (naphthalene-1,4-diyl) by Helix-sense-selective Polymerization and Circularly Polarized Light Irradiation.

Optically active poly(naphthalene-1,4-diyl) was prepared through helix-sense-selective polymerization of the corresponding monomers and also through circularly polarized light (CPL) irradiation, resulting in distinctive circular dichroism (CD) spectral patterns. Chirality of the helix-sense-selective polymerization -based polymer is ascribed to preferred-handed helicity while that of the CPL-based polymer to a non-helical, chiral conformation ('biased-dihedral conformation') with preferred-handedness which was stable only in the solid state. The helix of the helix-sense-selective polymerization-based polymer gradually racemized in tetrahydrofuran while it was stabilized by aggregate formation in a hexane-dichloromethane solution. Both helix-sense-selective polymerization- and CPL-based polymers exhibited efficient circularly polarized luminescence.

Photosensitization of TiO2 electrodes immobilized with chiral plasmonic Au nanocolloids by circularly polarized light irradiation.

Photosensitization of semiconductors by excitation of chiral plasmonic metallic nanostructures has attracted much attention, not only for the analysis and detection of circularly polarized light but also for its potential applications in chiral photosynthesis. Although there have been reports on the detection of semiconductor-sensitized current in chiral nanostructures precisely fabricated by physical vapor deposition and/or lithography techniques, there have been no studies using plasmonic metal nanocolloids synthesized by chemical processes. In this study, we report the establishment of a fabrication method for large-area chiral photoelectrodes and the semiconductor photosensitization phenomenon realized using chiral plasmonic nanoparticles. Chiral plasmonic Au nanoparticles prepared by previously reported colloidal methods were immobilized onto a TiO2 thin film electrode by electrophoresis. When TiO2 electrodes loaded with chiral Au nanoparticles synthesized using L-cysteine were irradiated with circularly polarized light, left circularly polarized light irradiation at a wavelength of 500-600nm generated a larger anodic photocurrent than right circularly polarized light irradiation at the same wavelength. This trend was reversed for TiO2 electrodes immobilized with colloidal Au nanoparticles synthesized with D-cysteine. From these results, we conclude that the efficiency of photocurrent generation by chiral plasmon excitation can be controlled by the polarization direction of the incident light.

Photomanipulatable colloidal clusters from the aggregation of azo molecular glass spheres.

Colloidal clusters with well-controlled shapes have attracted extensive interest in the fields of materials, chemistry, physics, and biology. This communication reports the controllable fabrication of photoresponsive colloidal clusters with a wide range of adjustable sizes and complex architectures through an approach of microsphere formation and fusion. The clusters of colloidal spheres were obtained via adding ethanol dropwise into a tetrahydrofuran solution of an isosorbide-based azo compound (IAC-4). In the process, the colloidal spheres with soft and sticky shells were first formed in the dispersion. After stirring at an appropriate rate and time, clusters composed of controlled numbers of colloidal spheres were obtained. With increasing stirring time, the colloidal spheres in the clusters underwent fusion transforming into a range of structures with particular architectures. The structure formation, evolution and control were investigated by scanning electron microscopy (SEM) and dynamic light scattering (DLS). Under linearly polarized light irradiation, colloidal spheres in the clusters in the solid state were observed to be stretched along the direction of electric-field oscillation and these clusters were thus transformed into complex particles with unique morphologies. This exploration can lead to a new methodology to effectively fabricate colloidal clusters with complex architectures and shed new light on colloidal packing and organization under the driving forces of extrinsic energy input.

High‐Sensitivity Polarized Light Detector of 2D WS2/Mo2CF2 Van Der Waals Heterostructure

The photogalvanic effect (PGE) generated under linearly polarized light irradiation has remarkable applications in 2D nanodevices. The PGE of 2D WS2/Mo2CF2 van der Waals (vdW) heterostructure can generate photocurrent and high sensitivity to polarized light. However, the PGE has less photogenerated current. On this basis, the photocurrent transport mechanism of PGE under low bias voltage is investigated. The results show that the photocurrent of the photon energy has , and dependence on the polarization angle θ under the considered external bias voltage. Under a bias voltage of 1.0 V, the maximum photocurrent of 3.7 eV photon energy in the zigzag direction can reach 4.61. Under a bias voltage of 1 V, the maximum photocurrent of 1.8 eV photon energy in the armchair direction can reach 6.71. The maximum photocurrents are in the order of 10−1 for both zigzag and armchair directions with 0 V bias. Furthermore, 2D WS2/Mo2CF2 vdW heterostructure has a stable and high extinction ratio. These results show that 2D WS2/Mo2CF2 vdW heterostructure is a potential candidate material for future optoelectronics in the visible light region.

Magnetic proximity enabled bulk photovoltaic effects in van der Waals heterostructures

The bulk photovoltaic (BPV) effect, a second-order nonlinear process that generates static current under light irradiation, requires centrosymmetric broken systems as its application platform. To realize measurable BPV photocurrent in spatially centrosymmetric materials, various schemes such as chemical doping, structural deformation, or electric bias have been developed. In this paper, we suggest that the magnetic proximity effect via van der Waals (vdW) interfacial interaction, a contact-free strategy, also breaks the centrosymmetry and generates large BPV currents. Using the ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ quintuple layer as an exemplary material, we show that magnetic proximity effect from $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ septuple layers yields a finite and tunable shift and injection photocurrents. We apply group theory and first-principles calculations to evaluate the layer-specific shift and injection current generations under linearly polarized light irradiation. We find that the magnetic injection photoconductivity that localized on the ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ layer can reach $>70\ifmmode\times\else\texttimes\fi{}{10}^{8}\phantom{\rule{0.16em}{0ex}}\mathrm{A}/({\mathrm{V}}^{2}\phantom{\rule{0.16em}{0ex}}\mathrm{s})$, so that a one-dimensional linear current density on the order of 0.1 mA/nm can be achieved under an intermediate intensity light. In addition to charge current, we also extend our discussions into spin BPV current, giving pure photogenerated spin current. The vertical propagation direction between the charge and spin photocurrents suggests that they can be used individually in a single material. Compared with previously reported methods, the magnetic proximity effect via vdW interface does not significantly alter the intrinsic feature of the centrosymmetric material (e.g., ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$), and its manipulation can be easily achieved by the proximate magnetic configurations (of $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$), interlayer distance, and light polarization.

Photomechanical Solid Polymers: Model for Pressure and Strain Induced by Photoisomerization and Photo-Orientation

Photoactive polymers are important for fundamental studies and applications in several area of photonics such as data storage and holography and nonlinear optics and photomechanics. The latter is perhaps one of the most important applications of such materials, since they act as light to mechanical energy transducers and move under light action. For example, azo-polymers irradiated by inhomogeneous resonant ultra-violet or visible light undergo molecular and macroscopic motion, at sub-glass transition temperatures by photoisomerization of the azo dyes. Our recent research in this field highlighted the fundamentals of mobility enhancement by light, including light-induced viscosity change and acceleration of relaxation times, and photomechanics, encompassing motions in gradients of actinic light leading to surface structuring and actuation. In this paper, we present an original model which predicts the creation of mechanical pressure, i.e., motion, by a photo-induced change in the occupied volume and length of anisometric isomers, and we give simple analytical expressions describing the dynamics of volume as well as strain change upon polarized light irradiation of photomechanic samples.

Enhanced valley polarization of graphene on h -BN under circularly polarized light irradiation

Graphene on $h$-BN (G/hBN) has a long period moir\'e superstructure owing to the lattice mismatch between two materials. The long periodic potential caused by the moir\'e superstructure induces modulation of the electronic properties of the system. In this paper, we numerically calculate the optical conductivity of G/hBN under circularly polarized light irradiation. The lack of spatial inversion symmetry in G/hBN induces valley polarization. Furthermore, valley polarization becomes most pronounced in the infrared and terahertz regions if the twist angle between two materials is close to zero for the nondoping case, however, it is insensitive to the twist angle for the hole-doped case. These results will serve to design valleytronics devices using G/hBN.

Photoresponsivity of asymmetrical dihydropyrene under circularly polarized light irradiation

Asymmetric 2,7-di-tert-butyl-10b,10c-dimethyl-2′,3′-dimethyl-pyrazino[2,3-e]dihydropyrene (DMPZ-DHP) was prepared by the annulation of diamino dihydropyrene with 2,3-butanedione. Optical resolution was achieved using chiral high-performance liquid chromatography systems after the photoisomerization of DMPZ-DHP to DMPZ-metacyclophane-diene (MCPD), and its Kuhn’s anisotropy factor (g = Δε/ε) was determined to be approximately 1.0 e −3 at 550 nm. [S]- and [R]-DMPZ-DHP were irradiated with 550nm left and right circularly polarized light (CPL), and photoisomerization was found to proceed more rapidly upon irradiating the [S]-isomer with right-CPL than with left-CPL and upon irradiating the [R]-isomer with left-CPL than with right-CPL. This suggests that CPL can be detected and analyzed using asymmetric DMPZ-DHP.

Photo‐Imprinting of the Helical Organization in Liquid‐Crystal Networks Using Achiral Monomers and Circularly Polarized Light

Control over molecular motion is facilitated in materials with highly ordered nanoscale structures. Here we report on the fabrication of cholesteric liquid-crystal networks by circularly polarized light irradiation, without the need for chiral dopant or plasticizer. The polymer network is obtained by photopolymerization of a smectic achiral diacrylate mesogen consisting of an azobenzene core and discrete oligodimethylsiloxane tails. The synchronous helical photoalignment and photopolymerization originate from the cooperative movement of the mesogens ordered in well-defined responsive structures, together with the flexibility of the oligodimethylsiloxane blocks. The resulting thin films show excellent thermal stability and light-induced memory features with reversible responses. Additionally, we demonstrate the fabrication of photo-patterned films of liquid-crystal networks with opposite helical senses. These findings provide a new method to make light-controllable chiroptical materials with exciting applications in optics and photonics.

Photo-Imprinting of the Helical Organization in Liquid-Crystal Networks Using Achiral Monomers and Circularly Polarized Light.

Control over molecular motion is facilitated in materials with highly ordered nanoscale structures. Here we report on the fabrication of cholesteric liquid‐crystal networks by circularly polarized light irradiation, without the need for chiral dopant or plasticizer. The polymer network is obtained by photopolymerization of a smectic achiral diacrylate mesogen consisting of an azobenzene core and discrete oligodimethylsiloxane tails. The synchronous helical photoalignment and photopolymerization originate from the cooperative movement of the mesogens ordered in well‐defined responsive structures, together with the flexibility of the oligodimethylsiloxane blocks. The resulting thin films show excellent thermal stability and light‐induced memory features with reversible responses. Additionally, we demonstrate the fabrication of photo‐patterned films of liquid‐crystal networks with opposite helical senses. These findings provide a new method to make light‐controllable chiroptical materials with exciting applications in optics and photonics.

Photoinduced deformation of amorphous polyimide enabled by an improved azobenzene isomerization efficiency

A newly designed azo-PI, without pre-stretching or polarized-light irradiation, exhibits reversible bending behaviors under alternate UV and visible light irradiation, providing a facile route to deformable 2D/3D structure actuators.

Photoresponsivity of Asymmetrical Dihydropyrene Under Circularly Polarized Light Irradiation

Photoresponsivity of Asymmetrical Dihydropyrene Under Circularly Polarized Light Irradiation

Extrinsic Chirality by Interference between Two Plasmonic Modes on an Achiral Rectangular Nanostructure

The optical near field (NF) induced by circularly polarized light (CPL) is a hot scientific topic. We observed a chiral NF intensity distribution on a series of achiral gold nanorectangular structures (Au-NRs) under CPL irradiation by using multiphoton photoemission electron microscopy (MP-PEEM). Additionally, the differential NF spectra under left and right CPL irradiation, which represent the asymmetry of the NF intensity distribution, were investigated. We propose an interpretation that the chiral NF intensity distribution on an achiral metallic nanostructure is extrinsically generated by the interference between two plasmonic modes by combining state-of-the-art MP-PEEM techniques and the classical oscillator model. Our interpretation well explains both the experimental and simulation results. Furthermore, the intensity of the NF and its phase angle of each mode under linearly polarized light irradiation were revealed to be critical factors for the generation of extrinsic chirality in the NF intensity distribution.

Directional mass transfer of azo molecular glass microsphere induced by polarized light in aqueous immersion media.

Photoinduced mass transfer of azo polymer and azo molecular glass has been intensively investigated under various light irradiation conditions simply using air as the ambient environment. In this work, in order to understand the effects of the surrounding medium on the light-induced process, azo molecular glass microspheres adhered on a substrate were immersed in water and different aqueous solutions, and their mass transfer behavior was investigated by irradiation with linearly polarized light. The microspheres in the aqueous media showed significant deformation through directional mass transfer upon light irradiation and transformed into a series of shape-anisotropic particles as revealed by microscopic observations. Compared with their counterparts upon light irradiation in air, the particles immersed in the aqueous media exhibited larger elongation parallel to the substrate and higher shape anisotropy. Optical simulation showed that this was caused by the alteration of the direction of the electric vibration of the refracted light at the medium–microsphere interface, which controlled the mass transfer behavior. On the other hand, the viscosity of the aqueous media showed no effect on the mass transfer process induced by the irradiation. The photo-thermal effect on the mass transfer behavior was ruled out as the thermal dissipation through a liquid is much more efficient than that through air. On the basis of this, this methodology was also successfully employed in the photo-fabrication of anisotropic submicron-sized periodic structures in aqueous medium. These observations can supply deep understanding of this fascinating process induced by polarized light and extend the scope of its applications.

Blue circularly polarized luminescent amorphous molecules with single-handed propeller chirality induced by circularly polarized light irradiation.

Preferred-handed propeller conformation was induced by circularly polarized light irradiation to three amorphous molecules with trigonal symmetry, and the molecules with induced chirality efficiently exhibited blue circularly polarized luminescence. In both chirality induction and luminescence, chirality appeared to be amplified due to intermolecular interactions through π-stacking.

The I/T curve coefficient for evaluating changes in neuromuscular excitability after polarized light irradiation - a placebo-controlled randomized trial

Introduction: PILER light affects the sensory and motor excitability of the tissue, and these changes may depend on the color of the filter used in the irradiations. Objective: To evaluate changes in neuromuscular excitability after PILER irradiation with different filters. To evaluate the usefulness of the I/T curve coefficient in neuromuscular excitability test. Material and methods: 60 healthy volunteers assigned to four groups: group v - without filter (n=15), group x - red filter (n=15), group y - blue filter (n=15), group z - placebo (n=15) had biceps brachii irradiated with PILER light. Outcome Measures: I/T curve coefficient for rectangular (■I/T coeff) and triangular (▲I/T coeff) pulses for sensory and motor excitability and the pressure pain threshold (PPT). Results: ■I/T coeff (p=0.0013) and ▲I/T coeff (p=0.0011) for sensory excitability increased significantly in the irradiated group. ■I/T coeff (p=0.0356) and ▲I/T coeff (p=0.0022) increased significantly after blue light irradiation. A significant increase in the▲I/T coeff (p=0.0439) in motor excitability was observed in the irradiated group. ■I/T coeff (p=0.0309) and ▲I/T coeff (p=0.0064) increased significantly after blue light irradiation. Conclusion: PILER light may reduce muscle excitability. Using a blue filter may increase the sensory threshold, and myorelaxation. Further experiments are necessary to confirm the usefulness of the I/T curve coefficient.

Momentum-selective optical absorption in triptycene molecular membrane

The optical properties of triptycene molecular membranes (TMMs) under the linearly and circularly polarized light irradiation have been theoretically studied. Since TMMs have the double-layered Kagome lattice structures for their $\pi$-electrons, i.e., tiling of trigonal and hexagonal-symmetric rings, the electronic band structures of TMMs have non-equivalent Dirac cones and perfect flat bands. By constructing the tight-binding model to describe the pi-electronic states of TMMs, we have evaluated the optical absorption intensities and valley selective excitation of TMMs based on the Kubo formula. It is found that absorption intensities crucially depend on both light polarization angle and the excitation position in momentum space, i.e., the momentum and valley selective optical excitation. The polarization dependence and optical selection rules are also clarified by using group theoretical analyses.

Photoinduced anisotropy of DR13/PMMA thin films upon irradiation at various wavelengths

Photoinduced anisotropy of poly(methyl methacrylate) (PMMA) thin film doped with disperse red 13 (DR13) dye isomers was investigated. This anisotropy was analyzed by measuring the temporal changes in the isotropic and anisotropic absorption coefficients for various pump wavelengths (both sides of the isobestic point). The rates for photoisomerization were determined as p515=0.41s-1 and p375=0.20s-1 under irradiation with circularly polarized pumping beam. After irradiation, the thermal relaxation was evaluated to be 0.052s-1. During irradiation with linearly polarized light, some abnormal phenomena were monitored in the early time. The mechanism of angular redistribution caused by linearly polarized light irradiation is discussed in detail.

Inorganic photovoltaic cells based on BiFeO3: spontaneous polarization, lattice matching, light polarization and their relationship with photovoltaic performance.

Inorganic ferroelectric perovskite oxides are more stable than hybrid perovskites. However, their solar energy harvesting efficiency is not so good. Here, by constructing a series of BiFeO3-based devices (solar cells), we investigated three factors that influence the photovoltaic performance, namely, spontaneous polarization, terminated ion species in the interface between BiFeO3 and the electrode, and polarized light irradiation. This work was carried out under the framework of the density functional theory combined with the non-equilibrium Green's function theory under a built-in electric field or finite bias. The results showed that (1) the photocurrent is larger only under a suitable electronic band gap rather than larger spontaneous polarization; (2) the photocurrent reaches the largest value in the Bi3+ ion-terminated interface than in the case of Fe3+ or O2- with the SrTiO3 electrode; (3) the photocurrent can be largely enhanced if the polarized direction of the monochromatic light is perpendicular to the spontaneous polarization direction. These results would deepen the understanding of some experimental results of BiFeO3-based solar cells.

Resonant light absorption and plasmon tunability of lateral triangular Au nanoprisms array

Optical characteristics and electric field distribution of triangular Au nanoprism in a unit and units array under polarized light irradiation were systematically studied by numerical simulation with finite difference time domain method. It is found that the plasmonic properties of the triangular nanoprism are dominated by the electric polarization rather than the wave propagation. The triangular nanoprism presents similar optical response with a strong dipole band under different wave propagations if the electric polarization vectors are parallel to the triangular cross section. The lateral triangular Au nanoprisms array possesses a large tunability of the plasmonic properties contributed from the combined influence of inter-particle distance, particles size, polarization angle and even environmental medium. From the plasmon band shift versus the refractive index, ultra-high local surface plasmon resonance sensitivity (509.96 nm/RIU, figure of merit=5.55) is reached at ∼850nm, making this array promising for biochemical sensing applications.