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We investigate the origins of 'de Vries-like' liquid crystalline behaviour by introducing an ethynyl spacer in the core of the tricarbosilane-terminated 5-phenylpyrimidine mesogens QL16-6 and QL17-6. The rationale for this structural change is based on the assumption that an ethynyl spacer would create more free volume in the core sub-layer and therefore decrease the orientational order parameter S2 in the SmA phase. The tricarbosilane-terminated mesogens WL41-5 and WL42-6 with a 5-(phenylethynyl)pyrimidine core in either a normal or inverted orientation were synthesised, and their mesomorphic and 'de Vries-like' properties characterised using polarised optical microscopy, differential scanning calorimetry, birefringence measurements, small–angle (SAXS) and 2D X-ray scattering. Reduction factors R derived from SAXS and optical tilt angle measurements suggest that neither WL41-5 (R = 0.49) nor WL42-6 (R = 0.80) exhibit 'de Vries-like' properties. The S2(T) profiles show an increase in orientational order with decreasing temperature and a sharp discontinuity at the SmA-SmC transition, which is consistent with 'de Vries-like' behaviour. However, the Leff(T) profiles suggest an increase in interdigitation that reduces the positive effect of increasing S2 in compensating for the molecular tilt. [ABSTRACT FROM AUTHOR]

The recent discovery of a new lyotropic liquid crystal phase, the structure and properties of which are analogous to the chiral ferroelectric smectic C-phase (SmC*) in thermotropics, was based on a tailored amphiphile structure in which a tilt-promoting mesogenic core was linked to a chiral diol-headgroup via a hydrophilic ethylene glycol spacer [J. R. Bruckner et al., Angew. Chem., Int. Ed., 2013, 52, 8934–8937]. However, so far there is only one example of this general amphiphile structure known to form the new lyotropic SmC* phase in mixtures with water and with formamide. In an attempt to systematically elucidate the underlying structure–property relations we now report two new amphiphiles leading to lyotropic SmC* phases. These amphiphiles are derived from the parent amphiphile structure by (i) an elongation of the hydrophilic ethylene glycol spacer and (ii) an exchange of the original 2-phenylpyrimidine core by an even more tilt-promoting fluorenone core. Our investigations also reveal that the formation of the lyotropic SmC* phase is highly sensitive to exchanging or enlarging a building block of the primary material. [ABSTRACT FROM AUTHOR]

A homologous series of tri-, di- and monocarbosilane mesogens with a 5-phenylpyrimidine core and a chiral (S,S)-2,3-difluorohexyloxy chain were synthesized and characterized. We show that shortening the carbosilane end-group has a detrimental effect on ‘de Vries-like’ properties, causing an increase in reduction factor R from 0.17 for the tricarbosilane QL32-6 to 0.38 for the monocarbosilane QL34-6, both at the point of maximum layer contraction upon transition from the orthogonal SmA* to the tilted SmC* phase. This increase in R correlates with an increase in birefringence Δn, a broadening in the SmA* temperature range and a decrease in optical tilt angle ϑopt in the SmC* phase, which are all consistent with an increase in orientational order and a decrease in lamellar order. The electroclinic effect (ECE) in the SmA* phase decreases with decreasing length of the carbosilane end-group, which is consistent with previous observations of high ECE in ‘de Vries-like’ liquid crystals. On the other hand, spontaneous polarization PS measurements suggest that polar ordering in the SmC* phase is not strongly dependent on R. [ABSTRACT FROM AUTHOR]

The chiral carbosilane-terminated liquid crystal 2-[(2S,3S)-2,3-difluorohexyloxy]-5-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl]pyrimidine (QL32-6) undergoes a smectic A*-smectic C* phase transition with a maximum layer contraction of only 0.2%. It exhibits an electroclinic effect (ECE) comparable to that reported for the ‘de Vries-like’ liquid crystal 8422[2F3] and shows no appreciable optical stripe defects due to horizontal chevron formation. [ABSTRACT FROM AUTHOR]

Smectic liquid crystals with ‘de Vries-like’ properties are characterized by a maximum layer contraction of ≤1% upon transition from the orthogonal SmA phase to the tilted SmC phase. A defining structural characteristic of most ‘de Vries-like’ materials is a nanosegregating element that strongly promotes the formation of smectic layers. We show herein the effect of varying the length of a nanosegregating carbosilane end-group on ‘de Vries-like’ properties in three series of 5-phenyl-1,3,4-thiadiazole mesogens with chloro-terminated alkoxy chains (QL13-n, QL18-n and QL19-n). Shortening the end-group from a tricarbosilane to a monocarbosilane causes a decrease in ‘de Vries-like’ character, as measured by the reduction factor R, which is consistent with a decrease in nanosegregation and quality of the lamellar ordering. Measurements of the orientational order parameter S2 by 2D X-ray scattering of smectic monodomains show a concomitant increase in S2 that is consistent with the hypothesis that ‘de Vries-like’ behavior in these materials arises from a combination of high lamellar order and low orientational order. The requirement of a nanosegregating structural element to achieve ‘de Vries-like’ behavior is confirmed by the characterization of the chloro-terminated mesogen 2-(6-chlorohexyloxy)-5-(4-hexyloxyphenyl)-1,3,4-thiadiazole (QL28-6/6), which undergoes a SmA–SmC transition with a maximum layer contraction of 4.1% and behaves like a conventional smectogen. [ABSTRACT FROM AUTHOR]

Smectic liquid crystals with ‘de Vries-like’ properties are characterized by a maximum layer contraction of ≤1% upon transition from the orthogonal SmA phase to the tilted SmC phase. In an effort to expand the library of ‘de Vries-like’ liquid crystals required for the formulation of chevron-free ferroelectric liquid crystal mixtures, we report the synthesis of a homologous series of tricarbosilane 5-phenylpyrimidine liquid crystals QL16-n using an improved synthetic route, and the characterization of their liquid crystalline and ‘de Vries-like’ properties. Measurements of orientational order parameters S2 and effective molecular lengths Leff by monodomain 2D X-ray scattering suggest that ‘de Vries-like’ behavior in series QL16-n is due to the combined effect of an increase in S2 and a decrease in bilayer interdigitation, thus causing a smectic layer expansion that compensates for the molecular tilt in the SmC phase. We also show how the optical tilt angle in the SmC phase may be optimized for SSFLC displays―without compromising ‘de Vries-like’ properties―by shortening the tricarbosilane end-group to a dicarbosilane. Two of the new materials reported herein, 5-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl]-2-hexyloxypyrimidine (QL16-6) and 2-hexyloxy-5-[4-(12,12,14,14-tetramethyl-12,14-disilapentadecyloxy)phenyl]pyrimidine (QL24-6) rank among the best ‘de Vries-like’ materials reported heretofore, with broad SmC phases and reduction factors R of 0.17 and 0.18, respectively, at a reduced temperature T−TAC = −10 K. We also show that inverting the orientation of the 5-phenylpyrimidine core in the homologous series QL17-n causes a suppression of ‘de Vries-like’ properties. These results suggest that non-covalent core–core interactions in the intercalated smectic bilayers formed by these mesogens may influence ‘de Vries-like’ behavior. [ABSTRACT FROM AUTHOR]

The use of the liquid-crystalline state to control the assembly of large (>5 nm) gold nanoparticles (NPs) is of considerable interest because of the promise of novel metamaterial properties of such systems. Here we report on a new approach for the preparation of large nematic gold NPs using a bifunctional capping agent that enables control over the particle size and serves as a linkage for subsequent functionalization with mesogenic groups. Properties of the NPs were characterized by HRTEM, NMR, DSC, TGA, UV/vis, OPM, and XRD studies. The results confirmed the formation of a stable nematic mesophase above 37.5 °C for NPs in the 6-11 nm size range. [ABSTRACT FROM AUTHOR]

A nematic twist cell having a thickness gradient was filled with a mixture containing a configurationally achiral liquid crystal (LC) and chiral dopant. A chiral-based linear electrooptic effect was observed on application of an ac electric field. This 'electroclinic effect' varied monotonically with d, changing sign at d=d0 where the chiral dopant exactly compensated the imposed twist. The results indicate that a significant chiral electrooptic effect always exists near the surfaces of a twist cell containing molecules that can be conformationally deracemized. Additionally, this approach can be used to measure the helical twisting power (HTP) of a chiral dopant in a liquid crystal. [ABSTRACT FROM AUTHOR]

Electroclinic measurements, in which an applied electric field E induces a rotation Δθ ([proportional]E) of the liquid crystal director about the electric field axis in a chiral environment, were performed on several configurationally achiral liquid crystals in the presence of an imposed helical director profile. This imposed twist establishes a chiral symmetry environment for the liquid crystal. It was observed that a conformationally racemic mesogen possessing a flexible phenyl benzoate core exhibits a measurable electroclinic response in the nematic phase. On the other hand, when the phenyl benzoate mesogen is mixed with a mesogen containing a rigid, conformationally achiral core (fluorenone), or with a racemic dopant with an axially chiral core that mimics a mesogen having rigid right- and left-handed conformations (2,2'-spirobiindan-1,1'-dione), the magnitudes of the electroclinic responses were found to decrease sharply, apparently going to zero when extrapolated to the pure 2,2'-spirobiindan-1,1'-dione or fluorenone limit. (Note that neither of these additives possesses a nematic phase.). The results suggest that the flexibility of the core and its ability to deracemize conformationally in order to compensate the elastic energy cost of the imposed twist is the primary mechanism behind the observed electroclinic response.

The synthesis of a novel class of organosiloxane oligopodes, based on an axially chiral binaphthalene core is described and their mesogenic properties are fully characterised.

An intriguing class of quinones that efficiently catalyze the air oxidation (overall hydroxylation) of arylboronic acids to the corresponding phenol is reported. Autocatalysis in the parent system is particularly efficient and leads to rapid, quantitative synthesis of quinones such as 4 from boronic acid 1 at room temperature using air as stoichiometric oxidant. The efficiency results from a balance between two-stage conjugate addition and migration with each step driven by aromatization of a naphthalene fragment.