Structures of Chiral Smectic-C Mesophases Revealed by Polarization-Analyzed Resonant X-Ray Scattering

We report polarization-analyzed, resonant x-ray diffraction at the sulfer K edge performed upon freestanding liquid-crystal films. Our studies of the thiobenzoate enantiomer 100TBBB1M7 yield the polarization states of resonant satellite peaks arising from characteristic superlattices in SmC sub A*, SmC sub (FI1)*, SmC sub (FI2)*, and SmC sub (alpha) phases. The observed polarizations agree with the clock model of chiral smectic C variants, and rule out other proposals made to date for these structures. Data from 10QTBBB1M7 racemate also support the clock model. Our resonant diffraction results from a thiophene liquid-crystal compound reveal the same superlattice periodicities seen in corresponding antiferro-and ferri-electric phases of 10OTBBB1M7.