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 free-standing liquid-crystal films. Our studies of the thiobenzoate liquid-crystal enantiomer 10OTBBB1M7 yield the polarization states of resonant satellite peaks arising from characteristic superlattices in the chiral smectic-C $\left(\mathrm{Sm}{C}^{*}\right)$ variant phases, including the antiferroelectric $\mathrm{Sm}{C}_A^{{}^{*}},$ ferrielectric $\mathrm{Sm}{C}_{\mathrm{FI}1\mathrm{}}^{*}$ and $\mathrm{Sm}{C}_{\mathrm{FI}2\mathrm{}}^{*},$ as well as $\mathrm{Sm}{C}_{\alpha }^{*}.$ 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 10OTBBB1M7 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 10OTBBB1M7.