Showing papers by "Quan Li published in 2006"

Blue Phase, Smectic Fluids, and Unprecedented Sequences in Liquid Crystal Dimers

Abstract: Several optically pure liquid crystal dimers with strong molecular chirality, synthesized by covalently linking an achiral bent-core unit with a bulky pro-mesogenic rodlike chiral entity through a flexible spacer, display amorphous blue phase, smectic phases, and new sequences.

Fluorine containing nonsymmetrical five-ring achiral banana-shaped compounds with columnar and synclinic antiferroelectric layered phases

Abstract: The phase transitional behavior of two homologous series of five-ring banana-shaped compounds comprising fluorine substituents synthesized through covalent linking of two chemically dissimilar rod-like anisometric cores (arms) to central 1,3-phenylene is reported. The novelty of these molecules originates from the fact that the molecules are highly nonsymmetrical. One of the arms, which is either salicylaldimine or Schiff base core, possesses two vicinal fluorine atoms at the terminal ring having a -decyloxy tail; while the -alkyl tail attached to the other arm was varied to realize a homologous series of compounds. The mesophases have been characterized by several complementary studies. The banana-shaped systems having short or medium alkyl chain lengths form apolar columnar (two-dimensional) structures, while on ascending the series, a polar smectic phase is stabilized. Detailed electro-optical investigations on one of the polar smectic phases revealed a synclinic antiferroelectric (racemic) ground state structure, which switches, as expected, to an anticlinic ferroelectric state by the application of an electrical field. At higher field strengths applied for an extended time interval, the anticlinic ferroelectric state switches to a synclinic ferroelectric (chiral) state. Upon field removal, these domains switch to an anticlinic antiferroelectric (chiral) state, which eventually nucleates to the original antiferroelectric synclinic (racemic) state. Remarkably, the associated spontaneous polarization value exceeds 800 nC cm, which is among the highest reported hitherto.

Improved liquid crystals for vertical alignment applications

Abstract: Liquid crystals with a large negative dielectric anisotropy are difficult to align vertically on silicon oxide surfaces and sometimes even on polyimides. An interesting method has been found to generate high quality vertical alignment by doping the host liquid crystal with materials that have a cyanogroup along their long molecular axis. The effect is explained by considering both long range and short range interactions between liquid crystal and the alignment layer. Using this method we propose a way to design new liquid crystal mixtures with large negative dielectric anisotropy that have improved aligning ability for applications requiring vertical alignment. The method also allows for increased birefringence.

Nanoscale discotic liquid crystalline porphyrins

Abstract: Novel nanoscale discotic liquid crystalline porphyrins, methods for their preparation, and device fabrication are disclosed. These compounds are capable of being used as high-efficiency photovoltaic materials, organic semiconducting materials, and organic light emitting materials.