Discotic (disc-like) molecules typically comprising a rigid aromatic core and flexible peripheral chains have been attracting growing interest because of their fundamental importance as model systems for the study of charge and energy transport and due to the possibilities of their application in organic electronic devices. This critical review covers various aspects of recent research on discotic liquid crystals, in particular, molecular design concepts, supramolecular structure, processing into ordered thin films and fabrication of electronic devices. The chemical structure of the conjugated core of discotic molecules governs, to a large extent, their intramolecular electronic properties. Variation of the peripheral flexible chains and of the aromatic core is decisive for the tuning of self-assembly in solution and in bulk. Supramolecular organization of discotic molecules can be effectively controlled by the choice of the processing methods. In particular, approaches to obtain suitable macroscopic orientations of columnar superstructures on surfaces, that is, planar uniaxial or homeotropic alignment, are discussed together with appropriate processing techniques. Finally, an overview of charge transport in discotic materials and their application in optoelectronic devices is given (234 references).

Discotic liquid crystals: a new generation of organic semiconductors

Light-driven phenomena both in living systems and nonliving materials have enabled truly fascinating and incredible dynamic architectures with terrific forms and functions. Recently, liquid crystalline materials endowed with photoresponsive capability have emerged as enticing systems. In this Review, we focus on the developments of light-driven liquid crystalline materials containing photochromic components over the past decade. Design and synthesis of photochromic liquid crystals (LCs), photoinduced phase transitions in LC, and photoalignment and photoorientation of LCs have been covered. Photomodulation of pitch, polarization, lattice constant and handedness inversion of chiral LCs is discussed. Light-driven phenomena and properties of liquid crystalline polymers, elastomers, and networks have also been analyzed. The applications of photoinduced phase transitions, photoalignment, photomodulation of chiral LCs, and photomobile polymers have been highlighted wherever appropriate. The combination of photoc...

Light-Driven Liquid Crystalline Materials: From Photo-Induced Phase Transitions and Property Modulations to Applications.

Field-Cycling NMR Relaxometry

Gas-phase spectroscopy lends itself ideally to the study of isolated molecules and provides important data for comparison with theory. In recent years, we have seen enormous progress in the study of biomolecular building blocks in the gas phase. The motivation for such work is threefold: (a) It is important to distinguish between intrinsic molecular properties and properties that result from the biological environment. (b) Gas-phase spectroscopy of clusters provides insights into fundamental interactions and into microsolvation. (c) Gas-phase data support quantum-chemical calculations. This review focuses on the current status of (poly)amino acids and DNA bases. Recent results help elucidate structure and hydrogen-bonded interactions, as well as showcase a successful interplay between theory and experiment.

/pdf/gas-phase-spectroscopy-of-biomolecular-building-blocks-be8closr8k.pdf

Gas-phase spectroscopy of biomolecular building blocks.

Density-functional theory (DFT) and its variations provide a fruitful approach to the computational modeling of the microscopic structures and phase behavior of soft-condensed matter. The methodology takes deep root in quantum mechanics but shares a mathematical similarity with a number of classical approaches in statistical mechanics. This review discusses different strategies commonly used to formulate the free-energy functional of complex fluids for either phenomena-oriented applications or as a generic description of the thermodynamic nonideality owing to various components of intermolecular forces. We emphasize the connections among different schemes of DFT approximations, their underlying assumptions, and inherent limitations. We also address extensions of equilibrium DFT to phenomenological theories for the dynamic properties of complex fluids and for the kinetics of phase transitions. In addition, we highlight the recent literature concerning applications of DFT to diverse static and time-dependent phenomena in complex fluids.

Density-Functional Theory for Complex Fluids

We present comprehensive results of the Monte Carlo (MC) simulations of the phase ordering dynamics in d = 2 nematic liquid crystals. We study a system of size N (2)(N = 512) with molecules confined to a 512×512 square lattice and report the results for two LC Hamiltonians: generalized Lebwohl-Lasher (GLL) model and r(-6) dependent anisotropic dispersion interaction potential. In these Hamiltonians a fourth-rank Legendre polynomial P4 interaction term is added to the usual second-rank P2 term. We find that in both the cases the presence of the P4 interaction term significantly influences the nematic domains morphology. Our numerical data show a diffusive growth law with a logarithmic correction: L(t) ∼ (t/ln t)(1/2).

Phase ordering kinetics in uniaxial nematic liquid crystals with second- and fourth-rank interactions.

For pt I see abstr A36734 of 1970 A preaveraged model which includes almost all interactions whose variations with intermolecular separation are r-6 and r-12, has been used to explain the observed transport coefficients of polar gases Experimental second virial coefficient data in conjunction with the force parameters determined from viscosity data have been used to estimate the molecular quadrupole moments The results for five molecules (SO2, NH3, H2O, CH3F, and CH3OH) have been reported The values of the molecular quadrupole moments obtained in this way are very reasonable and are in good agreement with the values derived from other sources Additive and nonadditive third virial coefficients have been calculated on the force parameters derived from the viscosity and second virial coefficient data

https://iopscience.iop.org/article/10.1088/0022-3700/7/8/019/pdf

Transport and equilibrium properties of polar gases. II. molecular quadrupole moments: additive and nonadditive third virial coefficients

Using a Landau-de-Gennes-type free-energy density expansion, we have analyzed the effect of high pressure on the smectic A-isotropic () phase transition temperature and nonlinear dielectric effect (NDE) of a homologous series 5-n-alkyl-2(4’-isothiocyanatophenyl)-1,3-dioxanes (nDBT). The pressure dependence of () transition temperature () is explained in terms of the pressure-dependent Landau coefficients associated with the order parameter coupling terms of the free-energy density expansion. We have shown that the transition remains first order even at the elevated pressures. We have investigated the temperature and pressure dependence of the NDE in the isotropic phase of transition. The role of alkyl chain length of the homologous series on the transition and NDE has been studied and has been found to be substantial. A close agreement between the theoretical and experimental results has been found.

The influence of high pressure on isotropic–smectic A transition and nonlinear dielectric effect in homologous series of nDBT

Based on a thermodynamic model, as developed by us [Singh A, Singh S. Thermodynamic model for the description of smectic C* and smectic A–smectic C* phase transition properties. Phase Trans...

Application of thermodynamic model to study the ferroelectric properties of biphenyl alkyloxy benzoate homologous series of SSFLC

We study the influence of induction interaction on the fundamental elastic properties of nematic liquid crystals using a theory based on density functional formalism. Numerical calculations for the elastic moduli associated with splay, twist and ‘bend’ modes of deformation are reported for a model system described by an interaction potential having a reference part and a perturbation part. The reference interaction is represented qualitatively by the Berne-Pechukas model. The perturbation potential is represented by the attractive interaction which is described by induction interaction. Results for elastic constants are reported for a range of molecular length-width ratio, polarizability, dipole moment, temperature and density. We find that the contribution of induction interaction is small but non-negligible. The contribution is sensitive to the values of molecular parameters and density.

Shri Singh

Papers

Phase ordering kinetics in uniaxial nematic liquid crystals with second- and fourth-rank interactions.

Transport and equilibrium properties of polar gases. II. molecular quadrupole moments: additive and nonadditive third virial coefficients

The influence of high pressure on isotropic–smectic A transition and nonlinear dielectric effect in homologous series of nDBT

Application of thermodynamic model to study the ferroelectric properties of biphenyl alkyloxy benzoate homologous series of SSFLC

The Influence of Induction Interaction on the Curvature Elasticity of Nematic Liquid Crystals