Photoswitching of ferroelectric liquid crystals using chiral thioindigo dopants: The development of a photochemical switch hitter

摘要

By virtue of its spontaneous polarization (P-S), a ferroelectric SmC* liquid crystal can be switched between two states corresponding to opposite molecular tilt orientations using an electric field, thus producing an ON-OFF light shutter between crossed polarizers. Considerable efforts have been made over the past decade to develop photonic FLC light shutters because of their potential uses in dynamic holography and optical data storage. The ON-OFF switching of a FLC light shutter can be triggered by light via a photoinversion of P-S using a photochromic dopant. The spontaneous polarization is a chiral bulk property that can be left-handed (negative) or right-handed (positive), depending on the absolute configuration of the chiral component of the SmC* phase. In the approach described herein, the magnitude of P-S is modulated via the photoisomerization of a chiral thioindigo dopant that undergoes a large increase in transverse dipole moment upon trans-cis photoisomerization. The sign of P-S is photoinverted using an "ambidextrous" thioindigo dopant containing a chiral 2-octyloxy side chain that is coupled to the thioindigo core and induces a positive P-S, and a chiral 2,3-difluorooctyloxy side chain that is decoupled from the core and induces a negative P-S. In the trans form, the 2,3-difluorooctyloxy side chain predominates and the net Ps induced by the dopant is negative. However, upon trans-cis-photoisomerization, the increase in transverse dipole moment of the 2-octyloxy/thioindigo unit raises its induced Ps over that of the decoupled 2,3-difluorooctyloxy side chain, and thus inverts the net sign of P-S induced by the dopant from negative to positive. (C) 2004 The Japan Chemical journal Forum and Wiley Periodicals, Inc. Chem Rec 3: 288-295; 2004: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10067.