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

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.