New Insights into the Thermal Stability of the Smectic C Phase

Subtle differences in the molecular structure of mesogens can lead to very different experimental polymorphisms. The smectic C (SmC) phase can actually be exhibited by one isomer and not the other, or the range of temperature can be completely different. Unveiling the deep connection between atomic structure and the very existence of the SmC phase will lead to the design of new performing liquid crystalline materials for ferroelectric or nonlinear optical applications. Our approach is based on running molecular dynamics simulation from an initial SmC arrangement of molecules. When the temperature is increased, the molecules automatically adjust in a more favorable organization. Such modification in the imposed initial self-assembly is governed by values of the nonbonded energies. Thanks to the combined use of simulation and experimental phase diagrams, we have unveiled part of the deep connection between atomic structure and the very existence of the SmC phase. The actual display of the SmC mesophase stems from a subtle balance between short-range interactions, which reveal arrangement of molecules within a smectic layer, and long-range interactions, which disclose organization of layers

Luminescent P‑Chirogenic Copper Clusters

P-chirogenic clusters of the cubanes [Cu₄I₄L₄] (L = chiral phosphine) were prepared from (+)- and (−)-ephedrine with L = (<i>S</i>)- or (<i>R</i>)-(R)­(Ph)­(<i>i</i>-Pr)P (with R = CH₃ (seven steps) or C₁₇H₃₅ (10 steps)) with e.e. up to 96%. The X-ray structure of [Cu₄I₄((<i>R</i>)-(CH₃)­(Ph)­(<i>i</i>-Pr)­P)₄] confirmed the cubane structure with average Cu···Cu and Cu···I distances of 2.954 and 2.696 Å, respectively. The cubane structure of the corresponding [Cu₄I₄((<i>S</i>)-(CH₃)­(Ph)­(<i>i</i>-Pr)­P)₄] was established by the comparison of the X-ray powder diffraction patterns, and the opposite optical activity of the (<i>S</i>)- and (<i>R</i>)-ligand-containing clusters was confirmed by circular dichroism spectroscopy. Small-angle X-ray scattering patterns of one cluster bearing a C₁₇H₃₅ chain exhibit a weak signal at 2θ ∼ 2.8° (<i>d</i> ∼ 31.6 Å), indicating some molecular ordering in the liquid state. The emission spectra exhibit two emission bands, both associated with triplet excited states. These two bands are assigned as follows: the high energy emission is due to a halide-to-ligand charge transfer, XLCT, state mixed with LXCT (ligand-to-halide-charge-transfer). The low energy band is assigned to a cluster-centered excited state. Both emissions are found to be thermochromic with the relative intensity changing between 77 and 298 K for the clusters in methylcyclohexane solution. Several differences are observed in the photophysical parameters, emission quantum yields and lifetimes for R = CH₃ and C₁₇H₃₅. The measurements of the polarization along the emission indicate that the emission is depolarized, consistent with an approximate tetrahedral geometry of the chromophores

Luminescent P‑Chirogenic Copper Clusters

P-chirogenic clusters of the cubanes [Cu₄I₄L₄] (L = chiral phosphine) were prepared from (+)- and (−)-ephedrine with L = (<i>S</i>)- or (<i>R</i>)-(R)­(Ph)­(<i>i</i>-Pr)P (with R = CH₃ (seven steps) or C₁₇H₃₅ (10 steps)) with e.e. up to 96%. The X-ray structure of [Cu₄I₄((<i>R</i>)-(CH₃)­(Ph)­(<i>i</i>-Pr)­P)₄] confirmed the cubane structure with average Cu···Cu and Cu···I distances of 2.954 and 2.696 Å, respectively. The cubane structure of the corresponding [Cu₄I₄((<i>S</i>)-(CH₃)­(Ph)­(<i>i</i>-Pr)­P)₄] was established by the comparison of the X-ray powder diffraction patterns, and the opposite optical activity of the (<i>S</i>)- and (<i>R</i>)-ligand-containing clusters was confirmed by circular dichroism spectroscopy. Small-angle X-ray scattering patterns of one cluster bearing a C₁₇H₃₅ chain exhibit a weak signal at 2θ ∼ 2.8° (<i>d</i> ∼ 31.6 Å), indicating some molecular ordering in the liquid state. The emission spectra exhibit two emission bands, both associated with triplet excited states. These two bands are assigned as follows: the high energy emission is due to a halide-to-ligand charge transfer, XLCT, state mixed with LXCT (ligand-to-halide-charge-transfer). The low energy band is assigned to a cluster-centered excited state. Both emissions are found to be thermochromic with the relative intensity changing between 77 and 298 K for the clusters in methylcyclohexane solution. Several differences are observed in the photophysical parameters, emission quantum yields and lifetimes for R = CH₃ and C₁₇H₃₅. The measurements of the polarization along the emission indicate that the emission is depolarized, consistent with an approximate tetrahedral geometry of the chromophores