Large Optical Activity Research Articles

Transmittance spectra expression for dye-doped cholesteric liquid crystal with large optical activity

ABSTRACT Dye-doped cholesteric liquid crystals (DDCLCs) with a homeotropic initial state are more practical due to their lower power consumption and higher security. However, achieving the homeotropic initial state necessitates the use of long-pitch DDCLCs. The conventional formula for determining the planar (P) state transmittance of DDCLCs is inadequate for calculating the P state transmittance of long-pitch DDCLCs with pronounced optical activity. Therefore, in the experimental calculations and fitting, optical activity was introduced to amend the conventional formula and expand the calculation range to include visible wavelengths (400 nm-800 nm). Following numerous validations, a modified formula for calculating the P-state transmittance of DDCLCs was derived, which yields results closer to the actual values when optical activity is significant. This modification is of great significance in the design of long-pitch DDCLCs.

Dual Applications of Cobalt-Oxide-Grafted Carbon Quantum Dot Nanocomposite for Two Electrode Asymmetric Supercapacitors and Photocatalytic Behavior.

Carbon materials, such as graphene, carbon nanotubes, and quantum-dot-doped metal oxides, are highly attractive for energy storage and environmental applications. This is due to their large surface area and efficient optical and electrochemical activity. In this particular study, a composite material of cobalt oxide and carbon quantum dots (Co3O4-CQD) was prepared using cobalt nitrate and ascorbic acid (carbon source) through a simple one-pot hydrothermal method. The properties of the composite material, including the functional groups, composition, surface area, and surface morphology, were evaluated by using various methods such as ultraviolet, Fourier transform infrared, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller, scanning electron microscopy, and transmission electron microscopy analysis. The electrochemical performance of the Co3O4-CQD composite has been studied using a three-electrode system. The results show that at 1 A g-1, the composite delivers a higher capacitance of 1209 F g-1. The asymmetric supercapacitor (Co3O4-CQD//AC) provided 13.88 W h kg-1 energy and 684.65 W kg-1 power density with a 96% capacitance retention. The Co3O4-CQD composite also demonstrated excellent photocatalytic activity (90% in 60 min) for the degradation of methylene blue dye under UV irradiation, which is higher than that of pristine Co3O4 and CQD. This demonstrates that the Co3O4-CQD composite is a promising material for commercial energy storage and environmental applications.

Tunable Optical Activity in Twisted Anisotropic Two-Dimensional Materials.

Twisted van der Waals structures exhibit a variety of unusual electrical and optical phenomena and could provide a powerful means for designing nanodevices with tunable chiral properties. However, programming intrinsic chiral properties of the film on the atomic scale remains a great challenge due to the limitations of fabrication and measurement techniques. Here, we report a highly tunable large optical activity of twisted anisotropic two-dimensional (2D) materials, including black phosphorus (BP), ReS2, PdSe2, and α-MoO3, by varying the twist angle between the stacked layers. The chirality can be deliberately tailored through the engineering of the symmetry, band structure, and anisotropy of 2D materials, demonstrating the high tunability of the chirality. The results show the highest thickness-normalized ellipticity value (13.8 deg μm-1, twisted ReS2) and ellipticity value (1581 mdeg, twisted BP) among the systems based on 2D materials. It is also shown that the chiroptical response exists in an extremely large spectral range from the visible to the infrared. Furthermore, the twisted ReS2 enabled spin-selective control of the information transformation. These results show that highly controllable chirality in twisted 2D anisotropic materials has considerable potential in on-chip polarization optics, nano-optoelectronics, and biology.

Strong and Broadband Pure Optical Activity in 3D Printed THz Chiral Metamaterials

AbstractOptical activity (polarization rotation of light) is one of the most desired features of chiral media, as it is important for many polarization‐related applications. However, in the THz region, chiral media with strong optical activity are not available in nature. Here, a chiral metamaterial (CMM) structure composed of pairs of vertical U‐shape resonators of “twisted” arms is studied, and it is revealed that it demonstrates large pure optical activity (i.e., optical activity associated with negligible transmitted wave ellipticity) in the low THz regime. The experimental data show polarization rotation up to 25° for an unmatched bandwidth of 1 THz (relative bandwidth 80%), from a 130 µm‐thickness structure, while theoretical optimizations show that the rotation can reach 45°. The enhanced chiral response of the structure is analyzed through an equivalent RLC circuit model, which also provides simple optimization rules for the enhancement of its chiral response. The proposed chiral design allows for easy fabrication via direct laser writing (DLW) and electroless metal plating, making the associated structures suitable candidates for polarization control applications.

Nanoparticle toxicity may cause testicular dysfunction

Nanoparticle toxicity may cause testicular dysfunction

Unusually strong, tunable, and nonreciprocal light trapping and absorption in helically structured magnetoactive media

We investigated the absorption properties of photonic structures with both large optical activity and magneto-optical activity parameters. The photonic structure is a periodic helical 1D medium in an external magnetic field. The magneto-optical activity parameter g change effects on the absorption nonreciprocity spectra for both linear and circular polarizations and those for unpolarized (natural) light were investigated. We showed that in certain cases, the external magnetic field leads to a strong increase in light trapping, absorption, and absorption nonreciprocity. This system can operate as a powerful light source and asymmetric and tunable wide range high absorber as well. We also investigated the dependence of Q (total energy absorbed in a finite spectral range) and its density on the layer thickness for different values of magneto-optical activity parameter g. With a change in the parameter g, the value of Q changes over a wide range (increasing or decreasing over 40 or more times), i.e., we have a broadly tunable and nonreciprocal integral absorption, again, for both polarized and unpolarized light. We showed that there are values of the parameter of magneto-optical activity at which the integral absorption does not depend on the polarization of the incident light.

Cocrystallization of Chiral 3d-4f Clusters {Mn10Ln6} and {Mn6Ln2}.

Cocrystallization of different metal nanoclusters facilitates the preparation of cluster-based nanomaterials with enhanced properties. Herein, two pairs of enantiomeric 3d-4f cocrystallization structures of clusters R/S-[Mn10Ln6] and R/S-[Mn6Ln2] (Ln = Dy for 1R and 1S, Y for 2R and 2S) have been reported. Compounds R/S-[Mn10Ln6][Mn6Ln2] exhibit a large optical activity and magneto-optic effect as verified by natural circular dichroism (NCD) and magnetic circular dichroism (MCD). In addition, alternating current (ac) magnetic measurements show that the chiral R/S-[Mn10Dy6][Mn6Dy2] cocrystallization structure displays slow magnetic relaxation with Ueff = 25.1 K.

Large Nonlinear Optical Activity of a Near-infrared-absorbing Bithiophene-based Polymer with a Head-to-head Linkage.

Although the production of near-infrared (NIR)-absorbing organic polymers with an excellent nonlinear optical (NLO) response is vital for various optoelectronic devices and photodynamic therapy, the molecular design and relevant photophysical investigation still remain challenging. In this work, large NLO activity is observed for an NIR-absorbing bithiophene-based polymer with a unique head-to-head linkage in the NIR region. The saturable absorption coefficient and modulation depth of the polymer are determined as ∼-3.5×105 cm GW-1 and ∼32.43%, respectively. Notably, the polymer exhibits an intrinsic nonlinear refraction index up to ∼-9.36 cm2 GW-1 , which is six orders of magnitude larger than that of CS2 . The maximum molar-mass normalized two-photon absorption cross-section (σ2 /M) of this polymer can be up to ∼14 GM at 1200 nm. Femtosecond transient absorption measurements reveal significant spectral overlap between the 2PA and excited state absorption in the 1000-1400 nm wavelength range and an efficient triplet quantum yield of ∼36.7%. The results of this study imply that this NIR-absorbing polymer is promising for relevant applications.

In Situ Polymerization of Chiral Poly(fluorene-alt-benzothiadiazole) Nanocomposites with Enhanced Chirality

Poly(fluorene-alt-benzothiadiazole) (PFBT) is a promising chiral polymer for use in metamaterials and other photonic applications, due to its large chiral optical activity at visible wavelengths. However, its usages are very limited, since it is not readily patternable into microstructures and challenging to apply to applications. In this paper, we demonstrate photo patterning of chiral PFBT/Achiral SU-8 photoresist to produce high quality structures while retaining the extraordinary chiral optical activity of our previously-reported PFBT/SU8 nanocomposite films. The ability to produce cleanly patterned microfeatures with high chirality may enable wider use of PFBT in chiral metamaterials and other photonic applications.

Crystallization-Driven Asymmetric Helical Assembly of Conjugated Block Copolymers and the Aggregation Induced White-light Emission and Circularly Polarized Luminescence.

Controlling the self-assembly morphology of π-conjugated block copolymer is of great interesting. Herein, amphiphilic poly(3-hexylthiophene)-block-poly(phenyl isocyanide)s (P3HT-b-PPI) copolymers composed of π-conjugated P3HT and optically active helical PPI segments were readily prepared. Taking advantage of the crystallizable nature of P3HT and the chirality of the helical PPI segment, crystallization-driven asymmetric self-assembly (CDASA) of the block copolymers lead to the formation of single-handed helical nanofibers with controlled length, narrow dispersity, and well-defined helicity. During the self-assembly process, the chirality of helical PPI was transferred to the supramolecular assemblies, giving the helical assemblies large optical activity. The single-handed helical assemblies of the block copolymers exhibited interesting white-light emission and circularly polarized luminescence (CPL). The handedness and dissymmetric factor of the induced CPL can be finely tuned through the variation on the helicity and length of the helical nanofibers.

Crystallization‐Driven Asymmetric Helical Assembly of Conjugated Block Copolymers and the Aggregation Induced White‐light Emission and Circularly Polarized Luminescence

AbstractControlling the self‐assembly morphology of π‐conjugated block copolymer is of great interesting. Herein, amphiphilic poly(3‐hexylthiophene)‐block‐poly(phenyl isocyanide)s (P3HT‐b‐PPI) copolymers composed of π‐conjugated P3HT and optically active helical PPI segments were readily prepared. Taking advantage of the crystallizable nature of P3HT and the chirality of the helical PPI segment, crystallization‐driven asymmetric self‐assembly (CDASA) of the block copolymers lead to the formation of single‐handed helical nanofibers with controlled length, narrow dispersity, and well‐defined helicity. During the self‐assembly process, the chirality of helical PPI was transferred to the supramolecular assemblies, giving the helical assemblies large optical activity. The single‐handed helical assemblies of the block copolymers exhibited interesting white‐light emission and circularly polarized luminescence (CPL). The handedness and dissymmetric factor of the induced CPL can be finely tuned through the variation on the helicity and length of the helical nanofibers.

Synthesis, DFT calculations, biological investigation, molecular docking studies of β-lactam derivatives

In this study β-lactam derivatives which include 1,3,4-thiadiazole and 1,3,4-oxadiazole structure (8a,b) have been achieved by cyclocondensation reaction. The synthesized compounds were investigated for antioxidant capacity and in vitro antiurease activity. The obtained compounds displayed good-moderate urease inhibiton results in comparison with thiourea, standard drug. Also, frontier molecular orbital analysis, reactivity descriptors (such as ionization energy (I), electron affinity(A), electro negativity(χ), chemical hardnesses (η) and chemical softness (S), chemical potential (μ) and global electrophilicity index (ω)), nonlinear optical properties (NLO) and molecular electrostatic potential (MEP) studied with DFT approach and B3LYP/6–311++G (d,p) level of theory. Nonlinear optical calculations presented that 7b and 8b have very large nonlinear optical activity. In addition, molecular docking studies were performed.

Experimental Spectroscopic and Theoretical Studies of New Synthesized Sulfonamide Derivatives

In this paper, two new Schiff bases (L1 and L2) derived from substituted salicylaldehyde and sulfamethoxazole/sulfisoxazole were synthesized. The synthesized structures were elucidated by experimental spectroscopic methods such as FT-IR, 1H-13C NMR, 1H, and 13C shielding tensors, and elemental analysis. The theoretical vibrational modes and nonlinear optical (NLO) properties have been computed by DFT/B3LYP/6-311G(d,p) method. Theoretical 1H and 13C shielding tensors were calculated with GIAO methods in CDCl3 with same level of theory. The results have shown that there is perfect harmony between the calculated parameters and recorded experimental data. The first order hyperpolarizabilities of the new synthesized compounds are 201.79 and 113.14 times larger than that of urea (0.3728 × 10–30 esu), respectively. According to evaluated results, the L1 and L2 present large nonlinear optical activity and are candidate molecules for nonlinear optical applications.

A General Recipe for Nondispersive Optical Activity in Bilayer Chiral Metamaterials

AbstractBy mimicking broken mirror symmetry of naturally existing chiral materials, and exploiting even stronger magnetoelectric coupling, large optical activity has been realized in chiral metamaterials over the past decade. Nevertheless, most of chiral metamaterials demonstrated so far exhibit highly dispersive optical activity due to their resonant response, which inevitably leads to a narrow operating bandwidth in terms of the optical rotatory power as well as the transmission. Herein, conditions for possessing nondispersive optical activity are derived based on a Lagrangian model for general bilayer chiral metamaterials, and the validity is experimentally confirmed in a microwave regime. It is shown that large nondispersive optical activity can be realized in bilayer chiral metamaterials where metallic apertures are arranged in each layer with high‐rotational symmetry and the off‐diagonal terms of the magnetic interlayer coupling tensor are nonzero while the electric counterparts are eliminated. In stark contrast to most previous chiral metamaterials, a nonzero constant polarization rotation angle is observed at the quasi‐static limit, which manifests the unique nonresonant characteristic of the proposed magnetically coupled bilayer chiral metamaterials. In addition to the geometrical controllability, the amount of polarization rotation and transmission bandwidth can be further increased by stacking magnetically coupled bilayer chiral metamaterials.

Large nonlinear optical activity of chromophores with divinylquinoxaline conjugated π-bridge

Two chromophores with π-deficient quinoxaline (Q) core in the π-electron bridge together with dibutylaniline (DBA) donor moiety and tricyanofuranyl (TCF) or dicyanovinyl (DCV) acceptor moieties have been synthesized to investigate their macroscopic nonlinear optical (NLO) activity in guest-host materials. A distinctive feature of the 7-DBA-VQPhV-TCF chromophore is predominance of negative solvatochromism over the positive one, which is quite rarely met for the chromophores manifesting inverse solvatochromic behavior as well as the blue shift of the absorption maximum compared to the chromophore FTC with divinylthiophene π-bridge. Introduction of quinoxaline moiety in the conjugated bridge promotes the increase of thermal stability: Td of both compounds is higher than 225 °C. Density functional theory was used to calculate the chromophores first hyperpolarizability (β). Quadratic NLO response characterized by d33 coefficient was measured by SHG technique for thin guest-host polymer films. The influence of chromophore content on the NLO coefficient of 7-DBA-VQPhV-TCF/PMMA film has been investigated and the d33 value of this film reaches 108 pm/V at 25 wt% load. The poled film 7-DBA-VQPh-DCV/PMMA shows twice smaller d33 values (30 pm/V) at the same chromophore load (20 wt%).

Enantiomeric resolution of helicochiral paddlewheel complexes and their infrared, Raman, UV–vis and X-ray optical activity

Linear polynuclear paddlewheel complexes-extended atom chains or metal strings-have provided attractive models for the study of metal-metal bonding, magnetism and conductivity since their discovery in the 1990s [1]. Their helicoidal chirality, arising from mutual steric hindrance of the 3-pyridyl protons, resulting in the twisting of the equatorial ligand around the axis (see figure), has been less studied. Nonetheless, in one of the few examples of chiral resolution, the obtained enantiomers of a trinickel complex showed a remarkably high specific rotation of 5000 deg•mL•g −1 •dm −1 [2], motivating us to seek a general technique for the chiral resolution of such racemates. We have developed a procedure based on anion exchange for the chiral resolution of [M3(dpa)4] 2+ salts (M = Co(II) or Ni(II), Hdpa = 2,2'-dipyridylamine). Homochiral arsenyl tartrate (AsT) salts promoted the selective crystallization of [-M3(dpa)4(MeCN)2](NBu4)2[-AsT]2, or [-M3(dpa)4(MeCN)2](NBu4)2[-AsT]2 in the P4212 space group. The enantiopure compounds demonstrated surprisingly large optical activities using UV-vis, Raman and infrared spectroscopy in solution and, for the cobalt derivatives, in the X-ray range at the Co K-edge in single crystals. An intense X-ray linear dichroism was observed in the orthoaxial crystal orientation, whereas it vanished in the axial confirmation, while the angular dependence of the circular dichroism spectra followed the expected (3cos 2 − 1) function, thus spectroscopically confirming the D4 crystal symmetry. X-ray magnetic circular dichroism and X-ray magnetochiral dichroism signals at the Co K-edge were not detected, likely due to a strongly delocalized spin density on the metal-metal bonded tricobalt core. Nevertheless, these results establish that chiral polynuclear paddlewheel complexes can be cleanly resolved using selective crystallization and demonstrate considerable optical activity in the infrared, UV-vis and X-ray energy ranges, thus potentially offering future perspectives in non-linear optics and asymmetric synthesis [3].

Giant Optical Activity in an All-Dielectric Spiral Nanoflower.

Optical activity is an effect of prominent importance in stereochemistry, analytical chemistry, metamaterials, spin photonics, and astrobiology, but is naturally minuscule. Metallic nanostructures are commonly exploited as basic elements for artificially producing large optical activity by virtue of surface plasmon resonance (SPR) on the nanostructures. However, their intrinsic high ohmic loss amplified by the SPR results in low energy efficiency and large photothermal heat generation, severely limiting their performance and practical utility. Giant optical activity by inducing magnetic resonance in an all-dielectric spiral nanoflower (spiral-flower-shaped nanostructure) is demonstrated here. Specifically, a large circular-intensity difference of ≈35% is theoretically predicted and experimentally demonstrated by optimizing the magnetic quadrupole contribution of the nanoflower to scattered light. The nanoflower overcomes the bottleneck of the traditional metallic platforms and enables the development of diverse chiroptical devices and applications.

Interplay between structure and chiral properties of polyfluorene derivatives

Design of supramolecular organization to produce large optical activity involves multiple factors either internal as external. In this paper, we report on the synthesis, systematic study and theoretical modeling of a series of chiral polyfluorene derivatives, whereby we identify the main parameters controlling the chiroptical activity of polymer films. For each polymer, five empirical/theoretical properties were chosen, due to their effect on the chirality parameter: glass transition temperature, dissymmetry factor, molar mass, helix tightness and the inverse of interconversion energy. We introduce a radar graph exhibiting the influence of chirality metric on these five parameters and their interplay. The polygonal area in the radar graph and the chirality parameter presented a direct relationship. Such graph can provide pre-screening of polymer properties, based on both experimental measurements and theoretical considerations and help choosing the right combination of parameters, leading to a material with the best properties.

A Terahertz Controlled‐NOT Gate Based on Asymmetric Rotation of Polarization in Chiral Metamaterials

Logical operation based on polarization encoding of light is important for future data transmission and information processing. However, in the terahertz (THz) region, chiral materials with large optical activity are not available in nature, and the effective manipulation of polarization states remains challenging. Here, the authors demonstrate a double‐layer bi‐anisotropic metamaterial that consists of planar spiral and cut‐wire layers separated by a polyimide film. Strong asymmetric polarization rotation of two orthogonal linear polarizations can be observed around 0.53 THz. By investigating the correlation between two linear polarization states before and after the spiral‐wire metamaterial at this frequency, a controlled‐NOT (CNOT) gate operating on two linear‐polarization‐based qubits is further exploited. The processing mechanism of the asymmetric rotation and CNOT gate is attributed to the scattering of dipole momentum based on classical multipole theory. This polarization processor's architecture is promising for robust and energy‐efficient THz polarization control, and also provides an effective path for the development of future optical supercomputing technology.

Induction of Circularly Polarized Luminescence from Europium by Amino Acid Based Ionic Liquids.

Materials that emit circularly polarized light have application in several important industries. Because they show large optical activity and emit sharp visible light transitions, europium complexes are often exploited in applications that require circularly polarized luminescence (CPL). Chiral and coordinating ionic liquids based on prolinate, valinate, and aspartate anions are used to induce CPL from a simple achiral europium triflate salt. The sign of the induced CPL is dependent on the handedness (l vs d) of the amino acid anion. Comparison of the CPL spectra in ionic liquid with proline and valine vs aspartate shows that the number of carboxylate groups in the amino acid anion influences the europium coordination environment. DFT calculations predict a chiral eight-coordinate Eu(Pro)4- structure in the prolinate ionic liquid and a chiral seven- or eight-coordinate Eu(Asp)33- structure in the aspartate ionic liquid.