Light Scattering from Macromolecular Systems - Molecular Crystals and Polymers

Section I Hydrodynamic Instabilities and Critical Phenomena.- To Scale or not to Scale? - The Puzzle at the Lambda Point of Liquid 4He.- Transition to Turbulence in Couette-Taylor Flow.- Hydrodynamic Instabilities and Turbulence.- Light from Gels and a Single Polymer Chain near Phase Transitions.- Interferometric Studies of Thick Film Critical Behavior.- Section II Physics in Two Dimensions and Defects.- Melting and Liquid Crystals in Two Dimensions.- Light Studies of Molecular Orientation Fluctuations in Two Dimensions.- Multiphonon Boundary of the Excitation Spectrum.- Raman Spectra of Proustite and Pyrargyrite Crystals in Low Temperature Phases.- Finite Field Local Field Catastrophe - Application to the Spectra of KCNxCl1?x.- The Effect of Long Range Fluctuations in Impurity Potential on the Electron Light in Heavily Doped Semiconductors.- Resonant and Trapping of 29 cm?1 Acoustic Phonons in Ruby Crystals.- Section III Non-Local and Transient Phenomena.- Some Aspects of the Theory of Surface Polaritons.- Recent Developments in Non-Local Optics.- Resonant Brillouin of Exciton Polaritons.- Ultraslow Optical Dephasing of Pr3+:LaF3.- Picosecond Raman Gain Studies of Molecular Vibrations on a Surface.- Section IV Spins and Excitons.- Brillouin-Mandelstam of Light in Antiferromagnetic CoCO3.- Observation of Pure Spin Diffusion Without Charge Transport by Spin Flip Raman Scattering.- Spin-Flip from Photoexcited Excitons in SiC.- The of Light by Spin Waves on Ferromagnetic Surfaces.- Relaxation of Energy and Polarization in the Resonant Secondary Emission Spectra of Semiconductors.- Resonant Raman from Stress-Split Forbidden Excitons in CU2O.- Low Frequency Exciton and Raman Spectra of CoCO3.- Theoretical and Experimental Determinations of Raman Cross Sections in Simple Solids.- Section V Resonance and Charge Excitations.- Resonant Secondary Emission by Impurities in Crystals.- The Raman and Hot Luminescence of Self-Trapping Excitons.- Phenomenological Description of Light and Thermal Radiation.- Raman from Plasmon-Phonon Coupled Modes in GaP.- Interaction Between Localized Carriers in the Accumulation Layer and Extended Bulk LO Phonons in InSb and GaSb: Raman Interference Lineshapes.- Inelastic Light by the Two Dimensional Electrons in Semiconductor Heterojunction Superlattices.- On the Distinction Between Resonant and Hot Luminescence: Application of Theory to Experiment.- Section VI Phase Transitions.- Light Near Structural Phase Transition Points in Pure Crystals and in Crystals Containing Defects.- Raman From Charge Density Waves and Superconducting Gap Excitations in 2H-TaSe2 and 2H-NbSe2.- Quasielastic Light Near Structural Phase Transitions.- High Resolution X-Ray and Light Spectroscopy of Liquid Crystals.- Optics and Electrooptics of Chiral Smectics.- The Size, Shape and Polydisperity of Micelles of Amphiphillic Molecules.- Resonance Raman Studies of Visual Pigments.- A Nanosecond Probe of Hemoglobin Dynamics Using Time Resolved Resonance Raman Scattering.- Section VII Multi-Photon Spectroscopy.- Recent Results in Four-Photon Spectroscopy of Condensed Media.- Recent Progress in Four-Wave Mixing Spectroscopy in Crystals.- Coherent Raman Ellipsometry of Liquid Water: New Data on the Vibrational Stretching Region.- Time Resolved Coherent Anti-Stokes Raman in Weakly Disordered Molecular Crystals.- Intense Light Resonance Scattering: Spectra and Photon Correlations.- Section VIII Resonance and Surface Enhanced Raman Scattering.- Intensity Effects in Resonance Light Scattering.- The Spontaneous Diffraction of Light by Resonance Atoms.- Raman by Molecules Adsorbed on Metals: an Overview.- Raman Spectroscopy of Molecular Monolayers in Inelastic Electron Tunneling Spectroscopy Junctions.- A Theory of Giant Raman Scattering by Adsorbed Molecules on Metal Surfaces.- Concluding Remarks.- Participants.- Author Index.

ConspectusMultifunctional integrated molecules are increasingly pivotal in various cutting-edge fields including materials science, nanotechnology, and biomedicine. Among these molecules, chiral fluorescent photoswitches (CFPSs) are a class of functional organic molecules that seamlessly integrate chiral, fluorescent, and photoresponsive characteristics. These properties, when combined, allow for a fascinating array of variations in chirality and fluorescence due to the structural changes induced by photoisomerization. The types of photoisomerization further influence these changes, resulting in a wide range of outcomes. In this Account, we present the progressive results of our ongoing research in the field of CFPSs, with a special emphasis on the dynamic regulation and photonics properties of chiral liquid crystal (LC) systems constructed with these molecular switches. To date, we have developed five different types of CFPSs based on α-cyanostilbenes, dicyanodistyrylbenzene, diaryldicyanoethene, sulfonated DAE, and azobenzene, respectively. We have actively explored the molecular engineering of these CFPSs, the performances of the chiral LC assemblies, and the constructed photonic devices that broaden their potential applications.The main focuses of this Account are structured around the concept of the "molecule engineering-properties-device applications" of the CFPSs. Crucially, CFPSs have the unique ability to amalgamate chiral and fluorescent properties within this photomodulation, serving as an effective medium to achieve sophisticated photomodulation effects. Given this, we focus on the molecular engineering of these CFPSs based on cyano positions, aryl modifications, linking sites, and binaphthyl handedness, which strongly affect the fluorescence intensity, emission wavelength, chiral-induction ability, photoisomerization conversion rate, and reversibility. The comprehensive analysis holds significant implications for guiding the future design and optimization of CFPSs. Furthermore, LC is a versatile enabling material that can integrate CFPSs to create self-assembled 1D helical superstructures known as cholesteric LC (CLC) or 3D blue-phase (BP) cubic structure systems. We reveal that these LC systems not only enable cross-scale regulation of CFPSs but also serve as highly efficient photonic devices in their own right. Such advanced photonic devices we constructed have the ability to adjust both the reflected color, the fluorescence properties, and circularly polarized luminescence (CPL), demonstrating significant potential for visual and smart applications.These systematic investigations emphasize the importance of the photoswitches' integrated chirality and fluorescence for optimized molecular design and fabrication, intrinsic regulation mechanism, and advanced photonic applications. Further systematic investigations, including molecular simulation, performance stability, and device friendship, will contribute to the rapid development of CFPSs-LC photonic devices that are suitable for practical applications.

Enhanced electrochemical and electro-optical properties of nematic liquid crystal doped with Ni:ZnCdS/ZnS core/shell quantum dots

Introduction. Liquid crystals (LC) are anisotropic optical media which have found broad application, in particular in LC displays and other photonic devices in the visible range. Little attention has been focused on studying LCs for conversion of radiation in the IR region of the spectrum, even though CO2 and other IR lasers are used in industry and medicine. Well-oriented nematic LC samples are strongly birefringent media, and are characterized by ordinary and extraordinary refractive indices no and ne. An electric field can change the orientation of LC molecules (the Frederiks effect), leading to a change in the effective refractive index along the direction of propagation of the light. In this case, the long axes of molecules of an LC with positive dielectric anisotropy are aligned parallel to the field direction, while in an LC with negative dielectric anisotropy they are aligned perpendicular to the field. This is a fundamental property of liquid crystals, and the basis for the operating principle of most photonic devices. Earlier in [1] a method was proposed for controllable filtration of IR radiation, based on a combination of the Frederiks effect and the Christiansen effect. The latter effect arises if particles are dispersed in a sufficiently transparent medium and the particle sizes are comparable with the wavelength of the incident light. In this case, the system transmits light in a narrow range of wavelengths, where the refractive indices are close for the particle material and the medium in which the particles are dispersed. Using LCs made it possible to control the position of the transmission maximum of the system when an electric field is applied. Application of this effect is also possible for a fixed value of the applied voltage (by varying its frequency). In this case, we propose using a dual-frequency LC as the medium in which the particles are dispersed, where the LC has positive anisotropy of the dielectric constant at low frequencies of the applied electric field and negative dielectric anisotropy at high frequencies. Aluminum oxide is used as the particle material; the refractive index of aluminum oxide varies considerably in the IR region of the spectrum [2]. In this paper, we present the results of a study of the Christiansen effect in an aluminum oxide particles — dual-frequency LC system.

In this work, some of the most important characteristics of chiral compounds as components of the liquid crystal (LC) systems are discussed. These characteristics are the helical twisting power of chiral dopants (CDs) in the induced cholesteric (N*) mesophases, the temperature dependence of the induced helical pitch (P) quantified by the dP/dT parameter and the influence of the CDs on the N* mesophase thermal stability characterized by the dTiso /dC parameter. The molecular structure influence on them for several systematic series of the N-arylidene derivatives of (S)-1-phenyl- and (S)-1-benzylethylamines as well as the chiral diastereomeric 2-arylidene-p-menthane-3-ones is considered.

The applications of elastic and quasielastic light scattering techniques to polymers in dilute solution, thermotropic liquid crystals and biological membrane vesicles are presented. It is focused on how we extract specific structural features or dynamic processes of these condensed medium samples through the light scattering methods. The paper reviews the light scattering studies that were carried out at the author's laboratory in Wisconsin from 1973 until 1980.

We point out that the global symmetries of the Yang-Mills theory in the Landau gauge support existence of variables similar to director fields in liquid crystal systems. We discuss two different types of the liquid crystal variables associated with the group of global Euclidean rotations and with a residual global group of color transformations. These global symmetries allow to identify various topological defects which resemble, in particular, vortex-like disclination defects and monopole-like objects in nematic liquid crystals. We suggest that the deconfinement phase transition in the Yang-Mills theory may be associated with a phase transition in a liquid crystal.

The intrinsic relative preferences of XX, XY and YY interactions between functional groups X and Y can be obtained by considering a set of onedimensional inclusion compounds containing guest molecu...

An important approach to understanding phase transitions in liquid crystals is to study systems in which the dominant interparticle interactions are hard repulsion, rather than the complicated interparticle potentials found in most liquid crystals. Computer simulations have shown [1] that a nematic to smectic A phase transition may exist in a system as simple as monodisperse hard rods. Experimentally, Xin Wen, Robert Meyer and Donald Caspar [2] have reported the observation of the smectic A ordering in tobacco mosaic virus (TMV) suspensions, in which the dominant interparticle interactions are screened electrostatic repulsion. In this paper we present the first quantitative measurements of the nature of the nematic to smectic A phase transition in TMV. In solutions in which the concentration is just below the transition concentration to the smectic phase, large pretransitional smectic fluctuations are observed. We will describe the methods of measuring the correlation lengths of these presmectic fluctuations by light scattering. In addition, the concentration difference between the smectic and the nematic phase close to the transition point is determined to be very small, implying that the transition is very close to second order. This result is consistent with the conclusion of numerous theoretical approaches [3], such as density functional theory and scale particle theory, which have concluded that a nematic to smectic A transition in a system of rigid rods should be second order or very close to second order.

<p dir="ltr">It has been shown that liquid crystals can be used as the basis for new types of biosensors that detect bacteria, viruses, and gases. The application of liquid crystal biosensors is relatively new in the biotechnology, medicine, and food industries. Over the past few decades, this advanced material has shown its potential in a variety of applications, including electro-optical devices. Liquid crystals are viscoelastic and anisotropic materials that respond to analytes and change their optical properties accordingly. As a result, changes in optical properties can be visualized and used to detect analytes. When the liquid crystal is in contact with an aqueous interface, the chemical or biological agent is adsorbed by the liquid crystal and results in a change in the liquid crystal orientation in film or within droplets. The result of changing the bulk orientation of liquid crystal creates a texture that can be visualized by optical methods, such as a polarizing optical microscope. Understanding liquid crystal biosensors requires an understanding of bulk orientation and interface interaction in various geometries. In addition to investigating the created texture or optical pattern when polarized light is transmitted through the liquid crystal system. This research will utilize a mathematical model and computational approach to gain an understanding of the liquid crystal biosensor's performance. In this study, biosensors with the aqueous interface will be examined. The unsteady two-dimensional mathematical model is composed of the Leslie Ericksen theory incorporating the Frank free energy during the usage of liquid crystal biosensors. The model is solved numerically using the Galerkin finite element method. We examined the transient optical pattern and response time with various initial bulk and boundary conditions. In nematic liquid crystal biosensors, surface viscosity and homeotropic anchoring strength are investigated and their impact is characterized. This series of studies has been presented for the first time for the use of liquid crystal biosensors with the aqueous interface.</p>

Linear and Nonlinear Polarizability: a Primer Second-Order Nonlinear Optical Processes in Molecules and Solids Third-Order Nonlinear Optical Effects in Molecular and Polymeric Materials Nonlinear Optical Properties of Molecules and Materials Electronic Hyperpolarizability and Chemical Structure Electrooptic Polymer Waveguide Devices: Status and Applications Waveguiding and Waveguide Applications of Nonlinear Organic Materials Nonlinear Optical Materials: The Great and Near Great Donor- and Acceptor-Substituted Organic and Organometallic Compounds: Second-Order Nonlinear Optical Properties Use of a Sulfonyl Group in Materials for Nonlinear Optical Materials: A Bifunctional Electron Acceptor Organic and Organometallic Compounds: Second-Order Molecular and Macroscopic Optical Nonlinearities Chemistry of Anomalous-Dispersion Phase-Matched Second Harmonic Generation Applications of Organic Second-Order Nonlinear Optical Materials Chromophore-Polymer Assemblies for Nonlinear Optical Materials: Routes to New Thin-Film Frequency-Doubling Materials Novel Covalently Functionalized Amorphous *y^2 Nonlinear Optical Polymer: Synthesis and Characterization Second-Order Nonlinear Optical Polyphosphazanes Molecular Design for Enhanced Electric Field Orientation of Second-Order Nonlinear Optical Chromophores Nonlinear Optical Chromophores in Photocrosslinked Matrices: Synthesis, Poling, and Second-Harmonic Generation Thermal Effects on Dopant Orientation in Poled, Doped Polymers: Use of Second Harmonic Generation Organic Polymers as Guided Wave Materials Observing High Second Harmonic Generation and Control of Molecular Alignment in One Dimension: Cyclobutenediones as a Promising New Acceptor for Nonlinear Optical Materials Strategy and Tactics in the Search for New Harmonic-Generating Crystals Development of New Nonlinear Optical Crystals in the Borate Series What is Materials Chemistry? Defect Properties and the Photorefractive Effect in Barium Titanate Defect Chemistry of Nonlinear Optical Oxide Crystals From Molecular to Supramolecular Nonlinear Optical Properties Control of Symmetry and Asymmetry in Hydrogen-Bonded Nitroaniline Materials Molecular Orbital Modeling of Monomeric Aggregates in Materials with Potentially Nonlinear Optical Properties Strategies for Design of Solids with Polar Arrangement Ferroelectric Liquid Crystals Designed For Electronic Nonlinear Optical Applications Model Polymers with Distyrylbenzene Segments for Third-Order Nonlinear Optical Properties Composites: Novel Materials for Second Harmonic Generation Clathrasils: New Materials for Nonlinear Optical Applications Inorganic Sol-Gel Glasses as Matrices for Nonlinear Optical Materials Intrazeolite Semiconductor Quantum Dots and Quantum Supralattices: New Materials for Nonlinear Optical Applications Small Semiconductor Particles: Preparation and Characterization Synthetic Approaches to Polymeric Nonlinear Optical Materials Based on Ferrocene Systems Transition Metal Acetylides for Nonlinear Optical Properties Third-Order Near-Resonance Nonlinearities in Dithiolenes and Rare Earth Metallocenes Nonlinear Optical Properties of Substituted Phthalocyanines Nonlinear Optical Properties of Substituted Polysilanes and Polygermanes Design of New Nonlinear Optic-Active Polymers: Use of Delocalized Polaronic or Bipolaronic Charge States New Polymeric Materials with Cubic Optical Nonlinearities: From Ring-Opening Metathesis Polymerization Polymers and an Unusual Molecular Crystal with Nonlinear Optical Properties Quadratic Electrooptic Effect in Small Molecules Third-Order Nonlinear Optical Properties of Organic Materials

In recent times it is known that some of disc­ like molecules exhibit a rich polymorphism of their mesophases similar to that of the liquid crystalline phases of rod-like molecules; among other meso phases the columnar phase, in which molecules form a columnar or tubular arrangement, is characteristic of the disc-like molecular liquid crystals. To date several kinds of the disc-like molecular liquid crystals exhibiting the columnar phase have been synthesized and their properties and phase transitions have been studied. It is reported that the crystalline phase changes into the columnar phase and the columnar phase is followed by the nematic or the isotropic phase as the temperature increases and in the columnar phase the columns always form a two-dimensional array, hexagonal or rectangular lattice but in each column the molecules are irregularly stacked.!) Since the polymorphism of the meso phases of the liquid crystals is attributable to the peculiar shapes of the molecules, it is of interest to study what type of the interaction potential between a pair of molecules makes the columnar phase possible. The phase transition of disc-like molecules has been theoretically studied by several authors. Katz has discussed the problem in the framework of the Landau theory.) A molecular mean field theory of the phase transition has been developed by extending McMillan's model) of smectic A;4) there the intermolecular potential was assumed to be the same one as was adopted by McMillan for the study about the smectic A-nematic­ isotropic transition of rod-like molecules. An approach by means of the cluster expansion technique has also been done for systems of molecules with a repulsive hard core potential;5) in the third virial approximation, it was shown that the columnar phase can exist. In this paper we study the phase transitions of the disc-like molecular liquid crystals by using a model potential of the Lennard-Jones type, where we adopt the lattice gas model and the Bragg­ Williams approximation treatment to calculate the partition function. Let us assume that nA atoms constitute a molecule which has a rigid structure and each atom belonging to one molecule is under the influence of potential energy of the Lennard-Jones type produced by every atom belonging to a neighbouring molecule and total of these interaction potential energy amounts to the interaction energy between the two molecules under consideration_ 6 ) The interaction potential energy is then given by

CHAPTER 4 - Light Scattering and Phase Transitions in Liquid Crystals

A mechanical molecular rotation model for liquid crystal (LC) systems is employed to evaluate phase transition temperature of fluorinated phenylbicyclohexane isomeric LC compounds. Results show that when a fluorine atom is substituted along the molecular long axis, an LC molecule acquires high rotational speed and its rotation becomes stable, thereby resulting in a better thermal stability of the nematic phase. A novel explanation is proposed for the behavior of the nematic-isotropic phase of the LC system when a heavy atom is substituted along the molecular long axis.

The possibility of precisely regulating and targeting drug release with mesophase or Liquid crystal drug delivery systems has drawn much attention recently. This review offers a thorough investigation of liquid crystal drug delivery systems with an emphasis on their mesogenic architecture. It describes the various liquid crystal forms such as thermotropic and lyotropic liquid crystals and their applicability in advanced drug delivery. Liquid crystals are used as excellent carriers due to their distinctive characteristics, such as stimuli-responsive drug delivery and sustained release patterns. Comprehending the materials that form mesophase provides insight into their distinct physiochemical characteristics and their use in drug delivery. This review highlights the important role lyotropic and thermotropic liquid crystals play in drug delivery, underscoring their considerable potential. The transition of thermotropic liquid crystals from their conventional technological applications to drug delivery has been studied. Nonetheless, a few challenges still need to be addressed, including formulation strategy refinement, regulating release rates, maximising the loading of hydrophilic drugs, and storage stability. In the pharmaceutical field, addressing these issues will open the door to a revolutionary paradigm that will revolutionise therapeutic outcomes and improve patient care.Graphical