Large Optical Rotations Research Articles

Tunable Optical Rotation in Twisted Black Phosphorus.

Black phosphorus (BP) is a typical two-dimensional (2D) layered material with strong in-plane anisotropy and large birefringence, making it possible to manipulate the light field with atomically controlled devices for various optoelectronic and photonic applications-for instance, atomic thickness waveplates. The twist angle in twisted black phosphorus (TBP) can be presented as a new tunable dimension to control BP's optical anisotropy. Here, we report a large and tunable optical rotation effect in TBP, the result of regulating the twist angle and BP thickness. To accurately study the optical rotation and the impact of the twist angle, we developed a new method to prepare TBP. A lab-made polarimeter microscope was used to visualize the optical rotation mapping of TBP. A large polarization-plane rotation (PORA) of 0.49° per atomic layer was observed from an air/BP/SiO2/Si Fabry-Pérot cavity at 600 nm, an order of magnitude higher than the PORA of 0.05° per atomic layer reported earlier. For the same thickness, the PORA of TBP can be tuned from 0.48° to 7.75° based on the twist angle from 0° to 90°. Our work provides an efficient method to investigate the anisotropy of 2D materials and their heterojunctions. TBP could help us design novel optical and optoelectronic devices such as tunable nanoscale polarization controllers.

Phase-Transition Optical Activity in Chiral Metamaterials.

Optical activity from chiral metamaterials is both fundamental in electrodynamics and useful for polarization control applications. It is normally expected that due to infinitesimally small thickness, two-dimensional (2D) planar metamaterials cannot introduce large optical rotations. Here, we present a new mechanism to achieve strong optical rotation up to 90° by evoking phase transition in the 2D metamaterials through tuning coupling strength between meta-atoms. We analytically elucidate such phenomenon by developing a model of phase-transition coupled-oscillator array. And we further corroborate our ideas with both numerical simulations and experiments. Our findings would pave a new way for applying the concept of phase transition in photonics for designing novel optical devices for strong polarization controls and other novel applications.

Synthesis, characterization and physicochemical properties of new chiral quinuclidinol quaternary ammonium salts

A new series of chiral quaternary ammonium salts (QASs) were successfully synthesized and characterized by FT-IR, NMR and MS. The thermal stability and melting point (mp) of the chiral QASs were measured. Moreover, basic physicochemical properties of the QAS solutions including density, viscosity, conductivity and specific optical rotation were investigated. The solution properties such as dissociation equilibrium constant (k) and critical micelle concentration (CMC) were deduced with theoretical methods. All QASs exhibited good thermal stability (decomposition temperature > 470 K) and large specific optical rotations (−228.12 to −156.83).

Helix‐sense‐selective copolymerization of triphenylmethyl methacrylate with chiral 2‐isopropenyl‐4‐phenyl‐2‐oxazoline

ABSTRACTThe asymmetric induction leading to a one‐handed helix was investigated in the anionic and radical copolymerization of triphenylmethyl methacrylate (TrMA) and (S)‐2‐isopropenyl‐4‐phenyl‐2‐oxazoline ((S)‐IPO), and highly isotactic copolymers with a reasonable optical activity were obtained. In the anionic copolymerization, the optical activity of the obtained copolymers depended on the polarity of solvents, and a highly optically active copolymer was produced in the copolymerization in toluene. The chiral oxazoline monomer functioned not only as a comonomer but also as a chiral ligand to endow the polymer with large negative optical rotation in the copolymerization with TrMA. The copolymers with small positive optical rotation were obtained in THF, indicating that IPO unit may work only as the chiral monomer that dictates the helical sense via copolymerization with TrMA. The isotacticity of the obtained copolymers depended on the contents of TrMA units in the copolymers, but was almost independent of the solvent for copolymerization. In the radical copolymerization, the obtained copolymers exhibited small optical activities. It seemed that the chiral monomer cannot induce one‐handed helical structure of TrMA sequences even if the sequences probably have a high isotacticity. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 441–447

Second-Harmonic Generation Optical Rotation Solely Attributable to Chirality in Plasmonic Metasurfaces.

Chiral plasmonic nanostructures, those lacking mirror symmetry, can be designed to manipulate the polarization of incident light resulting in chiroptical (chiral optical) effects such as circular dichroism (CD) and optical rotation (OR). Due to high symmetry sensitivity, corresponding effects in second-harmonic generation (SHG-CD and SHG-OR) are typically much stronger in comparison. These nonlinear effects have long been used for chiral molecular analysis and characterization; however both linear and nonlinear optical rotation can occur even in achiral structures, if the structure is birefringent due to anisotropy. Crucially, chiroptical effects resulting from anisotropy typically exhibit a strong dependence on structural orientation. Here we report a large second-harmonic generation optical rotation of ±45°, due to intrinsic chirality in a highly anisotropic helical metamaterial. The SHG intensity is found to strongly relate to the structural anisotropy; however, the angle of SHG-OR is invariant under sample rotation. We show that by tuning the geometry of anisotropic nanostructures, the interaction between anisotropy, chirality, and experimental geometry can allow even greater control over the chiroptical properties of plasmonic metamaterials.

Copper Promoted Oxidative Coupling of SnAP Hydrazines and Aldehydes to Form Chiral 1,4,5‐Oxadiazepanes and 1,2,5‐Triazepanes

SnAP (Sn (tin) amine protocol) hydrazine reagents and aldehydes undergo oxidative, copper mediated coupling to form substituted 1,4,5‐oxadiazepanes and 1,2,5‐triazepanes. Unlike all prior reactions involving SnAP reagents, the SnAP hydrazine reagents undergo a molecular oxygen‐assisted oxidative cyclization. The air‐ and moisture tolerant transformation accommodates a broad range of groups including electron‐rich, electron‐poor aromatic, heteroaromatic, and aliphatic aldehydes and is amenable to gram scale synthesis. These unusual, chiral heterocycles have unexpectedly large optical rotations, which may find use in optical materials.

Synthesis of Optically Pure Helicene Metallocenes.

Two types of ruthenocenes and a ferrocene coordinated by rac-9H-cyclopenta[1,2-c:4,3-c']diphenanthrenyl anion(s), a [7]helicene with a cyclopentadienyl moiety at the center of its skeleton, were successfully synthesized: mono-helicene ruthenocene 1 and its iron analogue 1Fe with one [7]helicene ligand bound to the central metal, and bis-helicene ruthenocene 2 with two [7]helicenes. Starting from a racemic mixture of the ligand precursor, rac-2 and meso-2 were obtained in a 7:3 ratio. Since the [7]helicene has a high racemization barrier, enantiomers of the complexes were isolated in their pure forms; they showed large optical rotations and intense circular dichroism (CD) responses.

Synthesis of Optically Pure Helicene Metallocenes

AbstractTwo types of ruthenocenes and a ferrocene coordinated by rac‐9H‐cyclopenta[1,2‐c:4,3‐c′]diphenanthrenyl anion(s), a [7]helicene with a cyclopentadienyl moiety at the center of its skeleton, were successfully synthesized: mono‐helicene ruthenocene 1 and its iron analogue 1Fe with one [7]helicene ligand bound to the central metal, and bis‐helicene ruthenocene 2 with two [7]helicenes. Starting from a racemic mixture of the ligand precursor, rac‐2 and meso‐2 were obtained in a 7:3 ratio. Since the [7]helicene has a high racemization barrier, enantiomers of the complexes were isolated in their pure forms; they showed large optical rotations and intense circular dichroism (CD) responses.

Synthesis and Chiroptical Properties of Hexa‐, Octa‐, and Deca‐azaborahelicenes: Influence of Helicene Size and of the Number of Boron Atoms

Four members of a new class of cycloborylated hexa-, octa-, and deca-helicenes (1 a-d) have been prepared in enantiopure form, along with two cycloplatinated deca-helicenes (1 d', 1 d1 ), further extending the family of cycloplatinated hexa- and octa-helicenes reported previously. The azabora[n]helicenes display intense electronic circular dichroism and large optical rotations; the dependence of the optical activity on the size of the helix (n=6, 8, 10) and the number of boron atoms (1 or 2) has been examined in detail both experimentally and theoretically. The photophysical properties (nonpolarized and circularly polarized luminescence) of these new fluorescent organic helicenes have been measured and compared with the corresponding organometallic phosphorescent cycloplatinated derivatives (1 a1 -d1 ).

Chirality Induced by the Interaction of C═C and C═X Bonds (X═CH2, NH, NH2+, O, and S) Separated by a Methylene Group.

The chirality derived from the interaction between two double bonds (C═C and C═X where X ═ CH2, NH, NH2+, O and S) across a methylene group has been examined in some detail at the B3LYP/aug-cc-pVTZ level. The rotamers of these formally achiral molecules that lead to large calculated specific rotations are those that allow overlap between the pair of double bonds, and the rotation is increased when the distance between them is decreased. Although the large specific rotation of unconjugated enones such as norbornenone is usually attributed to a magnetic transition dipole arising from an n-π* interaction of the carbonyl group, it has been found that large rotations may also be found with some conformations of unconjugated dienes such as 1,4-pentadiene. In the relative orientations of the double bonds that lead to large optical rotations, the pair of p-π orbitals are oriented so that they can interact leading to an electric transition dipole, while at the same time they are somewhat twisted with respect to each other allowing a significant magnetic transition dipole Other information was obtained by studying 2-propene-1-imine and its conjugate acid. The former gives only a small increase in optical rotation as compared to pentadiene. However, protonation at N leads to a large increase in optical rotation. This suggests that lone pairs have little effect on rotation, whereas the change in electronegativity has a large effect.

Enantio- and Stereoselective Cyclopolymerization of Hexa-1,5-diene Catalyzed by Zirconium Complexes Possessing Optically Active Bis(phenolato) Ligands.

Enantio- and stereoselective cyclopolymerization of hexa-1,5-diene was achieved by enantiomerically pure dichloro zirconium(IV) pre-catalysts 2 possessing chiral [OSSO]-type bis(phenolate) ligands (-)-1 and (+)-1 in combination with dried methylaluminoxane (dMAO) as an activator. The corresponding activities were recorded with quite high values up to 1,960 g mmol(2)-1 h-1 , which are extremely larger than those of the related complexes. The microstructure analysis for the PMCPs furnished by pre-catalysts (Λ,S,S)-2 and (Δ,R,R)-2 showed good isotacticity factors (α = 75-78%) and relatively high proportions of trans-cyclopentane rings (σ = 14-21%). These enantiomeric PMCPs exhibited large specific optical rotations ([α]D = +28 to +32° from (Λ,S,S)-2, -26 to -34° from (Δ,R,R)-2).

Large circular dichroism and optical rotation in titanium doped chiral silver nanorods

The circular dichroism of titanium‐doped silver chiral nanorod arrays grown using the glancing angle deposition (GLAD) method is investigated in the visible and near infrared ranges using transmission ellipsometry and spectroscopy. These films are found to have significant circular polarization effects across broad ranges of the visible to NIR spectrum, including large values for optical rotation. The characteristics of these circular polarization effects are strongly influenced by the morphology of the deposited arrays. Thus, the morphological control of the optical activity in these nanostructures demonstrates significant optimization capability of the GLAD technique for fabricating chiral plasmonic materials. image

Interlocked chiral/polar domain walls and large optical rotation in Ni3TeO6

Chirality, i.e., handedness, pervades much of modern science from elementary particles, DNA-based biology to molecular chemistry; however, most of the chirality-relevant materials have been based on complex molecules. Here, we report inorganic single-crystalline Ni3TeO6, forming in a corundum-related R3 structure with both chirality and polarity. These chiral Ni3TeO6 single crystals exhibit a large optical specific rotation (α)—1355° dm−1 cm3 g−1. We demonstrate, for the first time, that in Ni3TeO6, chiral and polar domains form an intriguing domain pattern, resembling a radiation warning sign, which stems from interlocked chiral and polar domain walls through lowering of the wall energy.

Optically active helical vinyl polymers via radical polymerization of (S)‐3‐vinyl‐2,2′‐bisalkoxy‐1,1′‐binaphthyl

Abstract(S)‐3‐Vinyl‐2,2′‐bisalkoxy‐1,1′‐binaphthyl (3) was synthesized via the Wittig reaction. Radical polymerization of all the monomers can take place smoothly in the temperature region tested. These polymers (poly‐3) showed very large specific optical rotations which were four times as large as those of the corresponding monomers 3. Poly‐3 displayed optical rotations and Cotton effects in the UV−visible absorption region of side groups which were different from the corresponding monomers 3 and the model compounds (S)‐3‐ethyl‐2,2′‐bisalkoxy‐1,1′‐binaphthyl (4). These facts imply the formation of helicity of the main chain and the helical conformations were quite stable demonstrated by the unchanged pattern of temperature variable circular dichroism spectra. © 2015 Society of Chemical Industry

Helical poly(phenylacetylene)s containing schiff-base and amino groups: Synthesis, secondary structures, and responsiveness to benzoic acid

Novel acetylenic monomers containing Schiff-base and amino groups, (S)-N-(4-ethynylbenzylidene)-1-phenylethanamine (1a), (R)-N-(4-ethynylbenzylidene)-1-phenylethanamine (1b), N-(4-ethynylbenzylidene)-1-phenylethanamine (1c), (R)-N-(4-ethynylbenzyl)-1-phenylethanamine (1d), and (R)-N-(4-ethynylbenzyl)-1-phenylethanamine (1e) were synthesized and polymerized with [(nbd)RhCl]2/Et3N catalyst to afford the corresponding polymers 2a-e with moderate molecular weights (Mn = 9000–60,000) in high yields (85–97%). All the polymers were soluble in common organic solvents including toluene, CHCl3, CH2Cl2, THF, and DMF. Large optical rotations and strong CD signals demonstrated that 2a, 2b, 2d, and 2e take helical structures with a predominantly one-handed screw sense. The effects of solvents and temperature revealed that these polymers took dynamic helical structure based on the steric effect of side groups. The CD patterns of 2d and 2e containing free amino moieties were completely inverted by the addition of benzoic acid. Upon further addition of NaOH, the CD pattern returned to the original one, indicating the reversible conformational change of these polymers according to pH. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5248–5256

Preparation of Phenylenevinylene Derivatives Having Fluorescence and Chiral Induction Function

A series of chiral rod-like compounds with fluorescence was synthesized. The chemical structures of the materials thus synthesized were confirmed with 1H nuclear magnetic resonance spectroscopy (NMR), 13C NMR, and two-dimensional heteronuclear multiple quantum correlation (HMQC) methods. Furthermore, guest-host type liquid crystal (LC) devices were prepared using these compounds and electric field driven optical rotation switching of the LC devices based on change in helix-uniaxial orientation was demonstrated. The large optical rotation is derived from the helical structure of the ordered cholesteric LC. (Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of Dispersion Science and Technology to view the free supplemental file.)

Synthesis and Chiroptical Properties of Arylimines of Cholest-4-ene-3,6-dione

In the hope of generating a new class of materials with large optical rotations, various arylamines were condensed with cholest-4-ene-3,6-dione (2) to give 3-arylimino steroids. These compounds possess moderately high specific rotations ([α](D) ~300-800) and strong circular dichroism. One such derivative, 3-(4-methoxyphenylimino)cholest-4-en-6-one (3), crystallizes as the (E)-imine and upon dissolution undergoes mutarotation to an equilibrium mixture of (E)- and (Z)-isomers with a half-life of approximately 1 h at room temperature, as judged by both NMR spectroscopy and polarimetry.

Analysis of Optical Activity in Terms of Bonds and Lone-Pairs: The Exceptionally Large Optical Rotation of Norbornenone.

Norbornenone, which has both a C═O and a C═C chromophore in a rigid bicyclic hydrocarbon framework, exhibits optical rotation (OR) an order of magnitude larger than that of similar molecules with only one of these chromophores (e.g., α-pinene). Its OR is also very sensitive to approximations in electronic structure calculations. The present study demonstrates a novel approach to interpret optical rotation using familiar concepts of chemical bonding, aided by first-principles calculations. A theoretical procedure is developed for analyzing the OR tensor components of a molecule in terms of individual bonds and lone pairs. The link between the chemist's bond and quantum mechanics is provided by localized molecular orbitals obtained from density functional theory (DFT) calculations. Delocalization of π orbitals is shown to play a crucial role in the large OR of norbornenone, as hinted by the DFT delocalization error inherent in many standard functionals and confirmed by detailed analysis. The OR contributions generated by the double bond in α-pinene are even stronger than that of norbornenone. The isotropic average, observed in solution or in gas phase, is small as a result of cancellation of tensor components with opposite signs. The electronic coupling and delocalization of the C═C π bond and the C═O oxygen π lone pair in norbornenone selectively enhance one of the OR tensor components, resulting in the exceptionally large negative isotropic OR.

Optical rotation in excess of 100 rad generated by Rb vapor in a multipass cell

Paramagnetic Faraday rotation is a powerful technique for atom sensing widely used in quantum nondemolition measurements, fundamental symmetry tests, and other precision measurements. We demonstrate the use of a multipass optical cell for Faraday rotation spectroscopy and observe polarization rotation in excess of 100 rad from spin-polarized Rb vapor. Unlike optical cavities, multipass cells have a deterministic number of light passes and can be used to measure large optical rotations. We also observe a tenfold suppression of transverse spin relaxation when Rb atoms are placed in a coherent superposition state immune to spin-exchange collisions.

Orientation of a Helical Nanofilament (B4) Liquid‐Crystal Phase: Topographic Control of Confinement, Shear Flow, and Temperature Gradients

The liquid-crystal (LC) phases of bent-core molecules have been of great interest because of their unusual polar and chiral properties, as well as their exotic collective behavior, including the formation of macroscopic chiral structures from achiral molecules. [ 1–9 ] The bent-core molecules strongly nanosegregate, leading to the formation of polar and chiral arrangements of the bent cores into planar or modulated layers. Subtle interactions between layers can be manipulated to produce a variety of ferroor anti-ferroelectric phases. Among the most mysterious and interesting of these new phases is the B4, a locally layered phase with hexatic or semicrystalline ordering of the layers, showing large optical rotation and light scattering which suggests a strongly chiral local structure. Recently, it has been shown that the B4 is a phase of spontaneously self-assembling helical nanofi laments (HNFs), the morphology of which is driven by a tendency for local saddle splay deformation of the semicrystalline layers. [ 7 ] These nanofi laments, shown in Figure 1 b for the bent-core material NOBOW (benzoic acid, 4-[(E)-([4-(nonyloxy)phenyl]imino) methyl]-,1,1’-(1,3-phenylene)ester) (Figure 1 a) grow from the higher temperature isotropic or fl uid bent-core phases with a well-defi ned pitch of the helical twist and lateral structure and dimensions. The bulk B4 is a close packing of HNFs in which the fi lament axes are parallel to one another and their layer twist becomes macroscopically coherent. In the fi lament growth process a nucleation event establishes the handedness of a fi lament and this handedness is transferred to subsequently growing fi laments to form large ( ≈ 100μ m dimension) homochiral domains with either right-handed and left-handed characteristics. Atomic force microscopy (AFM) imaging of the air/LC surface of the B4 reveals this bulk structure,