Blue phases and twist grain boundary phases (TGBA and TGBC) in a series of fluoro-substituted chiral tolane derivatives

Optical activity measurements in the smectic blue phases

“…Figure 4 shows that the optical activity in BP Sm 3 becomes more supercritical as the molecular chain length decreases. These results are in agreement with calorimetric measurements [3] and prove that BP Sm 3 behaves just like the classical BP3 as far as the optical activity is concerned [15]. Indeed, the length scale of the smectic fluctuations in BP Sm 3 is not large enough to be probed by visible light.…”

“…The data for the 14BTMHC compound are plotted in Figure 7, showing a rise of the optical activity when the wavelength decreases. This confirms that the BP Sm lattice parameter is in the UV-range, and a fit to equation (3) represented by the solid line in Figure 7 allows for an estimation: λ 0 = 320 nm (P = 0.21 µm if n = 1.5). This value is consistent with the pitch found by the GrandjeanCano method in the TGB A phase where P = 0.16 µm close to the BP Sm transition [3].…”

“…This confirms that the BP Sm lattice parameter is in the UV-range, and a fit to equation (3) represented by the solid line in Figure 7 allows for an estimation: λ 0 = 320 nm (P = 0.21 µm if n = 1.5). This value is consistent with the pitch found by the GrandjeanCano method in the TGB A phase where P = 0.16 µm close to the BP Sm transition [3]. Indeed, an increase of the pitch of about 30% is also observed at the transition from cholesteric to classical blue phases [17].…”

“…The smectic order is correlated with the orientational three-dimensional order and therefore gives information on the symmetry of the BP Sm unit cell. The BP Sm lattice parameter is in the UV-range [3], preventing any optical scattering of visible light (Kossel diagram technique), which is commonly used to find the symmetry of the classical blue phases [4]. The structure of the smectic blue phases has been investigated, and BP Sm 2 apa e-mail: grelet@brandeis.edu pears hexagonal [5] whereas BP SmA 1 exhibits a cubic symmetry [6].…”

“…Recently new chiral phases, called smectic blue phases (BP Sm ), have been discovered in a chiral series called nBTMHC, where n is the aliphatic chain length [3]. BP Sm appear adjacent to twist grain boundary phases with no intermediate cholesteric state.…”