Structures of chiral smectic-C mesophases revealed by polarization-analyzed resonant x-ray scattering

We report polarization-analyzed, resonant x-ray diffraction at the sulfur K edge performed upon freestanding liquid-crystal films. Our studies of the thiobenzoate liquid-crystal enantiomer 100TBBB1M7 yield the polarization states of resonant satellite peaks arising from characteristic superlattices in the chiral smectic-C (SmC*) variant phases, including the antiferroelectric SmCA*, ferrielectric SmCFI1* and SmCFI2*, as well as SmCalpha*. 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 the 100TBBB1M7 racemate also support the clock model. Our resonant diffraction results from a thiophene liquid-crystal compound reveal the same superlattice periodicities seen in corresponding antiferroelectric and ferrielectric phases of 100TBBB1M7. [S1063-651X(99)12411-5].