Charles A. Liberko

Self-assembled monolayers for liquid crystal alignment: simple preparation on glass using alkyltrialkoxysilanes

A simple procedure for the preparation of octadecylsiloxane self-assembled monolayers (SAMs) on float glass substrates is described. The method utilizes commercial octadecyltriethoxysilane, OTE: n-C18H37Si(OCH2CH3)3, as the SAM precursor, with deposition accomplished in toluene solution using n-butylamine as catalyst. This synthetic approach obviates the use of the problematic trichlorosilanes typically required for the preparation of high quality SAMs, and is characterized by a wide ‘process window,’ utilizing off-the-shelf reagents without special handling.

Smectic liquid crystal alignment using mechanically rubbed n-octadecylsiloxane self-assembled monolayers

In recent years a variety of techniques has appeared for the fabrication and manipulation of self-assembled monolayers (SAMs). This development now offers new tools for the study and control at the molecular level of the interaction of liquid crystals (LCs) with solid surfaces, a research area of great importance for liquid crystal applications. In this paper we show that mechanically rubbed octadecylsiloxane SAMs generate a novel surface alignment of LCs in which the in-plane surface anisotropy usually accompanying rubbing is operative, but only for smectics in which the mean molecular long axis, ṋ, is tilted from the layer normal. On our SAMs smectic phases align with the layers parallel to the SAM surface, and in tilted smectics the surface component of ṋ is along the rubbing direction. This anisotropy is absent in the nematic phases which align with ṋ strictly normal to the surface. This behaviour can be understood in terms of a rubbed SAM monolayer surface, which is low energy, molecularly smooth, and rendered anisotropic by the rubbing. UV irradiation of rubbed SAMs gave excellent planar alignment (ṋ parallel to the surface). This type of control over LC alignment has not been previously reported.

Design and synthesis of ferroelectric liquid crystals. 22. side-by-side dimers for nonlinear optics

Abstract Possessing excellent processibility on silicon integrated circuits and a thermodynamically stable polar supermolecular structure, chiral smectic C (C*) ferroelectric liquid crystals (FLCs) are promising materials for use in ultra-fast (>500 MHz) integrated electro-optic modulators. In order to realize this promise, however, it is necessary to obtain FLC materials with values of the electronic second order nonlinear optical (NLO) susceptibility χ(2) larger than have been reported to date. One way to achieve this goal is to obtain orientation of “large β” organic functional arrays, composed of two rings with a conjugating spacer unit, along the polar axis in the C* phase. Such long molecular groupings, however, typically orient along the director in LC phases, normal to the C* polar axis. We present herein the results of the initial investigation of an approach for achieving large χ(2) in FLCs. In this case orientation of the prototypical large β chromophore found in the dye Disperse Red 1 (DR1) is...

MIXED VALENCE IN CONJUGATED ANION RADICALS. SOLUTION AND SOLID STATE STUDIES

Abstract Electron localization in anion radicals of aromatic compounds built with two electrophores was studied using Vis, NIR, IR and ESR spectroscooy and electrochemistry. N,N′,-Bis (2,5-di-tert-butylphenyl)-2,3,6,7-anthracene-docarboximide anion radical has the odd electron mainly localized on the anthracene bridge. This contrasts with its diquinone analog, 1,4,8,11-pentacenetetrone, which has the odd electron localized on one quinone at a time. The anion radical of the tatrakis-(N-cyanoimine) derivative of 5,7,12,14-pentacenetetrone (3−) is delocalized. The solid state conductivity of the salts M+, 3− ranges from 10−4 S cm−1 for M=Bu4N to 0.4 S cm−1 for M=Na

Fostering creativity in students

A short, two step synthesis project for students in organic chemistry provides practical experience in scale up, purification, isolation, and modification of synthetic procedures.