Optical Rotatory Dispersion Measurements Research Articles

Reaction field induction self-amplification optical activity during polymerization in liquid crystal

A monomer having both chiral induction from nematic liquid crystal (LC) to cholesteric LC and polymerization activity was prepared. Addition of the compound to nematic LC induced the formation of a cholesteric liquid crystal in its chiral form. Subsequent electrochemical polymerization of the monomer produced an optically active polymer with a helical structure as confirmed by circular dichroism (CD) and optical rotatory dispersion measurements. While, the addition of the chiral monomer to an isotropic non-LC solution, and subsequent polymerization resulted a product with no clear optical activity. These results suggest that polymerization of the monomer in a cholesteric environment allows the formation of a polymer with high optical activity. Morphological imprinting from the matrix LC was confirmed by surface observation through polarizing optical microscopy. The chiral monomer changes the surrounding environment to grow into a more highly ordered helical structure. The matrix LC as the environment amplifies the optical activity with helical growth of the monomer during polymerization.

High-Precise Measurement of Optical Rotatory Dispersion Based on Weak Value Amplification

Chiroptical signals (generally very weak) play significant roles in chiral discrimination that bring great benefits in biochemistry, pharmacy, chemical, and so on. But, high-precise chiroptical detection is still a challenge. In this paper, a high-precise measurement of optical rotatory dispersion (ORD) based on weak value amplification (WVA) is presented. We proposed ORD detection method with parameter separation: by introducing complex coupling strength and dimensionless parameter “intensitiy contrast ratio” pointer, the ORD is only associated with the imaginary part of the weak value while circular dichroism (CD) is only associated with the real part. By designing a suitable WVA scheme, the ORD and CD can be measured separately. In the experiment, the reliability of the parameter separation method for ORD measurement is verified, and the precision reach the order of $10^{-6}$ rad. This method has a broad application prospect in biomedical sensing, medicine, chemical analysis and other fields.

Chiral Charge Carriers Chiralions for Polyaniline Examined with Optical Rotation Spectroelectrochemistry

In this study, the optical active polyaniline film was examined with optical rotatory dispersion (ORD) through change in potential with spectroelectrochemical method. Polyaniline is one of the representative conducting polymers. Preparation of polyaniline is convenient because synthesis of polyaniline can perform in water medium. Conducting polymers shows electrochromism via change in the electronic state upon electrochemical redox process. Polyaniline forms various electronic states such as emeraldine base, emeraldine salt, and pernigraniline. This change allows to color tuning through electrochemical method. Further, optically active polyanilines have been synthesized in the presence of (+) or (-)-camphorsulfonic acid (CSA) by electrochemical polymerization or chemical polymerization with ammonium persulfate (oxidizing agent). Both electrochemical method and chemical method produce polyaniline through radical polymerization process. Polyaniline emeraldine salt as prepared form of polyaniline is doped with CSA, showing optical activity in the circular dichroism. In this research, we carried out to synthesis of polyaniline in the presence of optically active CSA, according to previously reported method (by Wallace et al). Here, we have found that the polyaniline thus prepared showed optically active electrochromism via electrochemical redox process in circular dichroism spectroscopy measurements. In our previous study, we calculated the ORD spectra for the polymer by Kramars - Kronich (K-K) conversion from circular dichromism. In the present research, we successfully obtained experimental data of optical rotation-spectroelectrochemical result, as a first example of optical rotation control of natural optical activity for conjugated polymers based on electrochemical method. In the case of low potential for the polymer in the electrochemical redox process, the polymer shows intense optical rotation at visible wavelength range. On the other hands, higher potential at around 1 V affords to give doping process for the polymer, resulting generation of polaron as charge carrier, which shows optical activity at near infrared region. We referred this optical charge carrier as “chiral charge carrier chiralions”. The electrochemical oxidation equivalents to electrochemical doping from the polymer. In other words, electrochemical oxidation gives electrochemical doping which results change in degree of optical rotation for the polymer. The control of optical ration for materials can be driven by magnetic field (Faraday rotation), and electric field (Kerr rotation). We propose a new phenomenon as ‘‘electrochemical optical rotation’’. The electro-conductivity of the polymer is measured with four-probe method. The polymer which is electronic doped state with (+)-CSA as electric dopant for production of radical cation (polarons) or dication (bipolarons) as charge carriers and chiral inducer for twisting main-chain. The polymer film was synthesized as followed. First, electrochemical polymerization of aniline as a monomer was carried out in excessive optically active (+)-CSA with three electrode system consisting of working electrode (indium-tin oxide coated glass), counter electrode (platinum wire), and reference electrode (SCE) in water. The polymerization reaction is rapidly progressed with formation of polymer thin film onto the counter electrode. The polymer was washed with excess amount of water, acetone. The electroactive polymer film was thus deposited on the electrode was used for optical activity measurements. Cyclic voltammetry (CV) measurements were carried out for the resultant polymer (monomer free) deposited on to the ITO coated glass electrode. The CV results with change in scan rate from 10-100 mV/s indicates electroactive. Increase of scan rate increases current density for the polymer due to increase of diffusion of ion in the electrolyte solution. Oxidation signals of the polymer are observed due to change in electronic state of the polymer. Corresponding reduction signals against oxidation process are observed, indicating reversible redox activity for the polymer. ORD measurement reveled that the polymer film thus obtained is optically active. The polyaniline can be formed helical structure due to doping of optically active CSA. We carried out in-situ ORD measurement with potential change, evaluating electrochemical driven change in optical rotation. Chemical structure of the double layer polymer is examined with Fourie transform infrared optical absorption spectroscopy measurements which reveled this polymer is polyaniline, and CSA as a dopant. Ultra-violet optical absorption measurements for the polymer film indicates intense and wide range absorptions from invisible to infrared range as charge carriers the delocalized along the main-chain, indicating the polymers are conductive materials. The advantages of the polymer film are formation of self-standing redox activity, tuning of optical activity and color coordination. This paper reports novel function of control optical rotation with electrochemical method examined with spectroelectrochemistry. This concept can be a first example as optical rotation effect of electro-optically active conducting polymers. This paper reports the charge carries of helical polyaniline as chiralions can tune via electrochemical method.

Chiroptical anisotropy of crystals and molecules.

Optical activity, a foundational part of chemistry, is not restricted to chiral molecules although generations have been instructed otherwise. A more inclusive view of optical activity is valuable because it clarifies structure-property relationships however, this view only comes into focus in measurements of oriented molecules, commonly found in crystals. Unfortunately, measurements of optical rotatory dispersion or circular dichroism in anisotropic single crystals have challenged scientists for more than two centuries. New polarimetric methods for unpacking the optical activity of crystals in general directions are still needed. Such methods are reviewed as well as some of the 'nourishment' they provide, thereby inviting to new researchers. Methods for fitting intensity measurements in terms of the constitutive tensor that manifests as the differential refraction and absorption of circularly polarized light, are described, and examples are illustrated. Single oriented molecules, as opposed to single oriented crystals, can be treated computationally. Structure-property correlations for such achiral molecules with comparatively simple electronic structures are considered as a heuristic foundation for the response of crystals that may be subject to measurement.

Formation and decomposition of Poly(l-lactic acid) charge-transfer complex with iodine: A new molecular switch

PLLA forms a charge-transfer (CT) complex with iodine in trichloromethane solution with Keq = 24.8 ± 1.8 M-1, much higher than the Keq = 0.75 M-1 measured with the model compound ethyl lactate-iodine in CHCl3. The higher equilibrium constant of the PLLA-I2 complex suggests a special polymer-iodine interaction which was confirmed by optical rotatory dispersion (ORD) measurements, taking advantage of the fact that PLLA is an optically active polymer. In fact, ORD measurement shows an induced Cotton effect at 500 nm giving further support to the model of iodine accommodated inside the helical coils of PLLA chains in solution. The PLLA-I2 complex was found very stable if stored in the dark and in the cold (i.e. +10 °C). The PLLA-I2 complex shows both the growth of the CT bands in the electronic spectrum and the induced Cotton effect in the ORD spectrum after prolonged storage. However, the PLLA-I2 complex is sensitive to visible light and it dissociates upon irradiation, but in the dark the complex is restored again, so that the complex could be defined as “photoreversible”. Furthermore, the PLLA-I2 complex is thermoreversible as it dissociates when heated at +50 °C but the complex is restored in full when cooled down to +10 °C in the dark. With these quite unique photoreversible and thermoreversible properties the PLLA-I2 complex behaves as a molecular switch i.e. a molecular system that can be reversibly interconverted between two states A and B by an external action or stimulus. Molecular switches are of key importance in nanotechnological applications.

Electro-Optically Active Polyaniline-Polypyrrole Double Layer Polymer Semiconducting Composite

Optically active polyanilines have been synthesized in the presence of chiral camphorsulfonic acid (CSA) by electrochemical polymerization in water medium. Polyaniline forms various electronic states such as emeraldine base, emeraldine salt, and pernigraniline. As prepared polyaniline in the presence of (+)-CSA is called as emeraldine salt. In this case, (+)-CSA shows two functions as 1) electro-dopant and 2) chiral inducer for the polyaniline, producing radical cation (polarons) and diction (bipolarons) as charge carriers and one-handed helically twist for the main chain. In the present research, we succeeded to obtain double layer conductive polymer film consisting of polyaniline and polypyrrole with electrochemical method. Fig. 1 shows the structure of the double layer polymer film. The optical activity of the polymer film was examined with optical rotatory dispersion (ORD). The double layer supports strength of the polymer film form. Electrical conductivity of the polymer film is ca. 0.25 S/cm evaluated with four-probe method. We carried out synthesis of a single layer polyaniline with (+)-CSA with potentiostat with three electrode system, Pt counter electrode saturated calomel electrode (SCE) as reference, and the polymer as working electrode. Fig.2 shows the results. Five scans afford to produce green polymer film deposited on the indium-tin oxide (ITO) coated grass electrode. The polymer shows redox activity conformed with cyclic voltammetry (CV). Increase of scan rate provides increase of current density in the electrochemical measurement because of increase of diffusion of ionic species in the electrolyte solution. The single layer polyaniline film displays electrochemical driven change in optical rotation evaluated with in-situ ORD/CV. The double layer polymer film was synthesized as followed. First, electrochemical polymerization of aniline as a monomer was carried out in concentrated optically active (+)-CSA with two electrode system. An application of electric filed (3.0 V) between electrodes in the electrolyte solution was carried out. The electrochemical polymerization reaction is rapidly progressed for formation of polymer thin film onto the anode side. Continuously, pyrrole as another kind of monomer was added to the electrolyte solution. The sequential electrochemical polymerization process affords to yield polypyrrole layer deposited onto the polyaniline layer. ORD measurement revealed that the double layer polymer film thus obtained is optically active. The bottom layer of polyaniline can be formed helical structure due to combination with optically active (+)-CSA. The top layer of polypyrrole may also form helical structure with aid of (+)-CSA as chiral doping agent. Chemical structure of the double layer polymer (composite) is examined with Fourie transform infrared optical absorption spectroscopy measurements. This result indicates that the polymer composite consists of polyaniline, polypyrrole, and CSA. The composite shows intense and wide range optical absorptions from invisible to infrared range due to delocalized charge carriers along the main-chain. The advantages of double conductive polymer film are redox activity, tunable optical activity, and color coordination. Top layer of polypyrrole is black in color with no polish and good redox character, and polyaniline as the bottom layer displays electro-optical activity. This paper reports convenient method for preparation of double layer system with electrochemical method. Further variation can be expected using different type of monomers for construction of multi-layer conductive polymer composite. This concept can be a first example as an electro-optically active conducting polymer composite. Figure 1

Time‐Resolved Pump–Probe Measurement of Optical Rotatory Dispersion in Chiral Metamaterial

A plasmonic chiral metamaterial is fabricated from a thin Au film and exhibits static optical rotatory power (ORP) in the visible spectral range. Transient ORP is measured to clarify the temporal development of ORP using a circularly polarized light (CPL) pump beam. Three distinct transient behaviors of ORP are identified, resulting from different energy relaxation processes of hot electrons that occur during a period of a few picoseconds after pumping. Nonthermal hot electrons experience Lorentz force from an inverse Faraday effect and electron–boundary scattering, yielding a pump beam CPL helicity‐dependent transient ORP. Once hot electrons are in thermal equilibrium with the lattice, electron energy is distributed among the occupied states, as described by Fermi–Dirac statistics. Moreover, the transient ORP is independent of pump beam CPL helicity, well explained by the selection rule of electron excitation and two‐temperature model of the electron cooling process. Theoretical analysis of the transient ORP in terms of the energy relaxation of thermal hot electrons is carried out by introducing a temperature‐dependent dielectric function and finite‐difference time‐domain simulation. It is found that the magnitude of ORP at an elevated temperature is reduced to less than that at room temperature, agreeing well with the experimental observation.

Novel method for determination of optical rotatory dispersion spectrum by using line scan CCD.

A novel method is presented for rapid measurement of optical rotatory dispersion (ORD). Light passes through a polarizer, sample and analyzer, to a transmission grating that disperses the collimated light beam. A step-motor rotating stage controlled by a digital signal processor changes the analyzer orientation. The light power is measured by a charge-coupled device (CCD) after each rotating-stage step. The optical rotation angle for each wavelength is determined from the shift between two Malus curves obtained from each CCD pixel. The ORD spectrum is obtained by transforming the optical rotation angle into specific rotation. The ORD spectrum for a standard quartz tube demonstrates good continuity and agreement with reference data.

Optical-rotatory-dispersion measurement approach using the nonlinear behavior of the geometric phase.

We propose a method for high-sensitivity optical rotatory dispersion (ORD) measurement of optically active samples that takes advantage of the nonlinear behavior of the geometric phase (GP). To measure the GP as a function of wavelength, we use a multichannel Fourier transform spectrometer (MC-FTS) that is based on Savart plate birefringent-polarization interference, into which we newly insert a zeroth-order quarter-wave plate (QWP). The modified MC-FTS allows us to measure the wavelength dependence of the GP and thus that of the optical rotation angle due to the sample. In this paper, we describe the proposed approach and demonstrate proof-of-principle experiments.

Disposable Plasmonics: Plastic Templated Plasmonic Metamaterials with Tunable Chirality.

Development of low-cost disposable plasmonic substrates is vital for the applicability of plasmonic sensing. Such devices can be made using injection-molded templates to create plasmonic films. The elements of these plasmonic films are hybrid nanostructures composed of inverse and solid structures. Tuning the modal coupling between the two allows optimization of the optical properties for nanophotonic applications.

Intrinsic Optical Activity and Large-Amplitude Displacement: Conformational Flexibility in (R)-Glycidyl Methyl Ether.

The dispersive optical activity of (R)-(-)-glycidyl methyl ether (R-GME) has been interrogated under ambient vapor-phase and solution-phase conditions, with quantum-chemical analyses built on density functional (B3LYP and CAM-B3LYP) and coupled-cluster (CCSD) implementations of linear-response theory exploited to interpret experimental findings. Inherent flexibility of the heavy atom skeleton leads to nine low-lying structural isomers that possess distinct chiroptical and physicochemical properties, as evinced by marked changes in the magnitude and the sign of rotatory powers observed in various media. These species are interconverted by independent motion along two large-amplitude torsional coordinates and are stabilized differentially by interaction with the surroundings, thereby reapportioning their relative contributions to the collective response evoked from a thermally equilibrated ensemble. The intrinsic behavior exhibited by isolated (vapor-phase) R-GME molecules was calculated through use of both conformer-averaging and restricted vibrational-averaging procedures, the former affording moderately good agreement with measurements of optical rotatory dispersion (ORD) and the latter providing strong evidence for sizable effects arising from vibrational degrees of freedom. A similar conformer-averaging ansatz based on the polarizable-continuum model (PCM) for implicit solvation was deployed to elucidate R-GME specific-rotation parameters acquired for six dilute solutions. This approach gave reasonable predictions for sodium D-line (589.3 nm) experiments performed in the extremes of solvent polarity represented by cyclohexane and acetonitrile but failed to reproduce the overall shape of ORD profiles and suggested more complex processes might be involved in the case of an aromatic medium.

Use of a modified Drude's equation to investigate the optical rotation property of sugars

Sugar compounds (glucose, xylose, arabinose, and galactose) and their mixed solutions were examined using the optical rotatory dispersion (ORD) measurement technique with a modified Drude's equation. Commonly, spectroscopic methods utilize the observation of absorption bands which are, in the case of sugars, located in the UV-spectral range. However, the polarization method used in this study allows us to investigate sugar samples in a convenient visible spectral range where sugar solutions are relatively transparent. The ORD set-up can be simple and robust as we will demonstrate: the self-constructed apparatus consists of only two linear polarizers, placed one after the other, with the angle between their transmission axes adjusted to 45°. The sugar solution sample in a cuvette was put between the polarizers. The set-up was connected to a sample compartment of a commercial UV–vis spectrophotometer. The method provided us the specific optical rotation and concentration of sugar solutions with a reasonable accuracy. In addition, the optical rotation value for mixed sugars has been found to be the average optical rotation value of individual sugar content. Beside use in the laboratory environment, the method could also have industrial on-site monitoring applications, for example in bio fuel production.

Diastereomeric preference of a triply axial chiral binaphthyl based molecule: a concentration dependent study by chiroptical spectroscopies.

We have examined the effects of environmental perturbations, specifically solvents and concentrations, on axial chirality of a recently synthesized axially chiral binaphthyl fluorene based salen ligand, named AFX-155, {[2,2'-(1E,1'E)-(R)-1,1'-binaphthyl-2,2'-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(4-((7-(diphenylamino)-9,9-dihexyl-9H-fluoren-2-l)ethynyl)-phenol)]}. Chirality and dominant conformations of AFX-155 in CDCl3 solvent have been characterized using vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy in combination with DFT calculations. AFX-155 exhibits triple axial chirality: one is at the binaphthyl ring and the other two are related to the axes of chirality along the -C-N bonds where Cs are part of the binaphthyl group. To evaluate solvent and concentration dependence, complementary VA and VCD experiments in both THF-d8 and CDCl3 have been performed, as well as the optical rotatory dispersion (ORD) and electronic CD (ECD) measurements in CDCl3 under much diluted conditions. While the binaphthyl chirality is determined by the synthetic route, the results show that the latter two axial chirality labels of the dominant diastereomers are concentration dependent. Under much diluted conditions, R-binaphthyl, R_intra_HB//R_extra_HB (R-RR) is favoured, whereas R-binaphthyl, S_intra_HB//S_extra_HB (R-SS) is the dominant species in a concentrated solution. This diastereomeric interconversion is found to be independent of the two solvents used. To provide insights into this interesting finding, conformational searches and the related spectral simulations have been carried out at the DFT/B3LYP/6-31G(d) level.

Liquid crystal stepwise electropolymerization – an approach to create insect photonic structure

Production of optically active or inactive laminate structures with particular morphology can provide new functional optical materials. In this study, a stepwise polymerization enables production of triple-layer films consisting of [cholesteric LC order]–[nematic LC order]–[cholesteric LC order]. This method realizes preparation of laminate structure from one kind of polymer with differing molecular orientations in each layer. The optical properties of the multi-layer thin films were examined with optical absorption spectroscopy, circular dichroism, and optical rotatory dispersion measurements. The polymer shows electrochemically driven change in optical activity. Thin polymer films consisting of the three layers (cholesteric–nematic–cholesteric orders) show turquoise blue as a structural color. The color can be tuned by electrochemical redox processes based on an electrochemical doping mechanism for π-conjugated polymers. This result demonstrates that the multi-layer organic semi-conducting polymer with liquid crystal order shows structural color with multi-layer interference mechanism.

Optical Rotatory Dispersion Measurement of D-Glucose with Fixed Polarizer Analyzer Accessory in Conventional Spectrophotometer

In the sample compartment of a conventional spectrophotometer, mounting of a polarizer before sample and an analyzer behind sample allows the determination of the optical rotatory dispersion of optical active media by measurement of the transmission ratio of crossed and parallel arranged polarizer and analyzer. A formula for the determination of the angle of rotation is derived from the transmission ratio. The arrangement is applied to determine the molar optical rotation of D-glucose in water in the wavelength range from 220 nm to 820 nm.

Exploring Light and Life

Exploring Light and Life

Experimental methods for measuring optical rotatory dispersion: Survey and outlook

The measurement of optical rotation (OR) and optical rotatory dispersion has been finding renewed interest for some years, because of advancement in computational methods and in the performance of new experiments. Here, we shortly review the traditional and most-used experimental methods. We define and discuss the two main types of approaches in measuring OR: the intensity method and the optical null method. We report on some new results obtained by redesigning experiments based on the first approach, by adapting nonsophisticated hardware to current circular dichroism instrumentation.

The aggregation of chlorhexidine digluconate in aqueous solution from optical rotatory dispersion measurements.

Journal Article The aggregation of chlorhexidine digluconate in aqueous solution from optical rotatory dispersion measurements Get access J H Perrin, J H Perrin School of Pharmacy, University of Wisconsin, Madison, Wisconsin 53706, USA Search for other works by this author on: Oxford Academic Google Scholar E Witzke E Witzke School of Pharmacy, University of Wisconsin, Madison, Wisconsin 53706, USA Search for other works by this author on: Oxford Academic Google Scholar Journal of Pharmacy and Pharmacology, Volume 23, Issue 1, January 1971, Pages 76–77, https://doi.org/10.1111/j.2042-7158.1971.tb12791.x Published: 11 May 2011 Article history Received: 09 September 1970 Published: 11 May 2011

The optical rotatory dispersion of some N-decyl-N-N-dimethylalanine salts and their critical micelle concentrations.

Abstract The optically active salts of N-decyl-NN-dimethylalanine are shown to have anomalous optical rotatory dispersion curves and to not be fully ionized in aqueous solution. The position of the peak in the 225 to 230 mμ region varies with concentration of the surfactant as does the molecular rotation at a given wavelength. The positions of the peaks and the molecular rotations at these low wavelengths are pH sensitive. The change in molecular rotation with concentration enables the critical micelle concentrations of L and D N-decyl-NN-dimethylalanine hydrobromides to be determined by optical rotatory dispersion measurements, the results agreeing well with the values calculated from the literature. The change in rotation on micelle formation appears to be due to a change in the degree of ionization of these weak acids, a fact which is confirmed by pH measurements on these solutions.

Phase sensitive detection of vibrational optical activity free-induction-decay: vibrational CD and ORD

Optical activity is manifested by chiral molecules including natural products and drugs, so that circular dichroism (CD) and optical rotatory dispersion (ORD) measurements can provide invaluable information on their chiro-optical properties and structures. It is experimentally demonstrated that heterodyne-detected Fourier-transform spectral interferometry with a femtosecond infrared pulse can be used to fully characterize the phase and amplitude of vibrational optical activity free-induction-decay field. The measured spectral interferograms are then converted to the linear optical activity susceptibility whose imaginary and real parts correspond to vibrational CD and ORD spectra. Unlike the conventional differential measurement technique, the present method based on a heterodyned interferometry is shown to be quite robust and stable. We anticipate that the present vibrational optical activity measurement technique will be of critical use in elucidating chiro-optical properties and structural changes in biomolecules.