Photoswitchable Bent-Core Nematic Liquid Crystals with Methylated Azobenzene Wing Exhibiting Optic-Field-Enhanced Fréedericksz Transition Effect

We have investigated two new series of unsymmetrical
four-ring
bent-core molecules with methylated azobenzene wings exhibiting nematic
mesophase. The difference between the two series was in the relative
position of the methyl (−CH3) substituent with respect
to the azo (−NN−) linkage in the molecule. Single-crystal
X-ray diffraction analysis unravels significant insights into the
spatial molecular arrangement and molecular stacking interactions
of these bent-core systems. The materials were able to show photoswitching
behavior and photomasking effect in the liquid-crystalline state via
nematic to isotropic (order to disorder) transition when illuminated
with UV light. In solid state, the materials exhibit photochromism
upon UV light exposure. One of the representative compounds (2/12) was studied to observe the optically enhanced Fréedericksz
transition (FT) effect stimulated by UV light intensity. A prototype
of phase grating has also been devised based upon the observed FT-enhanced
effect that has a prospect in certain photonic devices of dynamic
and reversible light manipulation.