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

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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 achieved by incorporation of the chromophore into a side-by-side dimer structure. Characterization of C* mixtures incorporating the new dopant at concentrations up to 30% by weight shows that indeed the DR1 chromophore can be oriented along the polar axis in FLCs with a moderate degree of polar stereocontrol.

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