Key developments in ionic liquid crystals

Ionic liquid crystals are materials that combine the classes of liquid crystals and ionic liquids. The first one is based on the multi-billion-dollar flat panel display industry, whilst the latter quickly developed in the past decades into a family of highly-tunable non-volatile solvents. The combination yields materials with a unique set of properties, but also with many challenges ahead. In this review, we provide an overview of the key concepts in ionic liquid crystals, particularly from a molecular perspective. What are the important molecular parameters that determine the phase behavior? How should they be introduced into the molecules? Finally, which other tools does one have to realize specific properties in the material?Published versio

Local lamellar organisation of discotic mesogens carrying fluorinated tails

Contains fulltext : 34551.pdf (publisher's version ) (Open Access)A series of disc-shaped liquid crystals, monomers and dimers, have been investigated. A spacer linked to the pentakis( phenylethynyl) phenoxy core of the mesogens was substituted with perfluorinated chains to investigate the microphase segregating effect of such groups. The nematic phase, commonly found for these mesogens, is strongly stabilised by the presence of the fluorinated groups. X-Ray diffraction studies indicate clearly the onset of nanophase segregation in the nematic phase. Remarkable is the result, that the nanophase segregation directs the systems towards a lamellar organisation, rather than the columnar order that is commonly found for disc-shaped mesogens. This is also confirmed by the order in the underlying crystalline phase. X-Ray diffraction studies of the nematic phase show the characteristics of cybotactic smectic clustering, which has not been observed for discotic systems so far

1H-1,2,3-triazole: from structure to function and catalysis

The heterocyclic family of azoles have recently become one of the most widely used members of the N-heterocycles; the most prominent one being 1H-1,2,3-triazole and its derivatives. The sudden growth of interest in this structural motif was sparked by the advent of click chemistry, first described in the early 2000s. From the early days of click chemistry, when the accessibility of triazoles made them into one of the most versatile linkers, interest has slowly turned to the use of triazoles as functional building blocks. The presence of multiple N-coordination sites and a highly polarized carbon atom allows for metal coordination and the complexation of anions by both hydrogen and halogen bonding. Exploitation of these multiple binding sites makes it possible for triazoles to be used in various functional materials, such as metallic and anionic sensors. More recently, triazoles have also shown their potential in catalytic systems, thus increasing their impact far beyond the initial purpose of click chemistry. This report gives an overview of the structure, functionalities, and use of triazoles with a focus on their use in catalytic systems

Crosslinking of fibrous hydrogels

In contrast to most synthetic hydrogels, biological gels are made of fibrous networks. This architecture gives rise to unique properties, like low concentration, high porosity gels with a high mechanical responsiveness as a result of strain-stiffening. Here, we used a synthetic polymer model system, based on polyisocyanides, that we crosslinked selectively inside the bundles. This approach allows us to lock in the fibrous network present at the crosslinking conditions. At minimum crosslink densities, we are able to freeze in the architecture, as well as the associated mechanical properties. Rheology and X-ray scattering experiments show that we able to accurately tailor network mechanics, not by changing the gel composition or architecture, but rather by tuning its (thermal) history. Selective crosslinking is a crucial step in making biomimetic networks with a controlled architecture

Tunable properties based on regioselectivity of 1,2,3-triazole units in axially chiral 2,2′-linked 1,1′-binaphthyl-based copolymers for ions and acid responsiveness

The synthesis and optical studies of a new chiral binaphthyl-based polymeric sensor are described herein. The polymers were prepared using the copper-catalyzed azide–alkyne cycloaddition reaction between fluorene and binaphthyl monomeric units. Resulted polymers differ in the orientation of the 1,2,3-triazole unit as a linker in polymeric backbone based on monomeric character. The responses of these polymers to both exposure to metal ions and the acidic medium were investigated by UV–vis absorbance, circular dichroism and fluorescence analysis. The changes in the absorption, chiroptical and fluorescence properties of the polymers indicate a change of the dihedral angle between the two naphthalene units on the binaphthyl moiety and tunability in conjugation. Moreover, an influence of regioselectivity of 1,2,3-triazole unit in polymer backbone in regards to complexation was discussed. The modulation in signal was detected in real time and makes this system a suitable candidate for further applications as an ion sensor or acid-responsive material