Preparation, structural and NLO-optical characterization of LB-molecular films from asymmetric Bent-Core liquid crystals

Molecular mono- and multilayered films of a polar asymmetric bent-core ("banana-shaped") liquid crystalline (LC) compound with hydrocarbon end-chain were prepared by the Langmuir-Blodgett (LB) technique. Langmuir films were characterized by surface pressure isotherms and Brewster angle microscopy (BAM). Likwise, LB-films deposited onto glass substrates were characterized by UV-VIS spectroscopy, the optical second hermonic generation (SHG) technique and atomic force microscopy (AFM). Results show that the asymmetric structure of bent-core liquid crystals may promotes and unstable multi-layered (n > 10 LB-layers) LB-architecture which leads to a rapid collapse of Z-type arrangements, giving rise to a drastic decrease of the nonliner optical (NLO) properties and film quality, Indeed, measurements evidence a tolerable and uniform molecular coverage on the glass substrates with anisotropic orientational distribution for a moderate number of layers only (n hyperpolarizability B_(off)-coefficient along the polar axes of the 2D-polar LC-compound within the mechanical stable LB-monolayer arrangements.