Liquid Crystals
The liquid crystalline state has been heavily investigated over the last decades and countless applications employing liquid crystalline molecules have been established.[1] Among the most popular applications, smart glass[2] as well as liquid crystal displays found in smartphones, TVs and laptops should be mentioned. Solution processability, self-assembly and self-healing make liquid crystals an important class of compounds for the next generation of organic electronics such as organic solar cells,[3] organic field effect transistors[4] and organic light emitting diodes.[5] The suitability of a liquid crystal for a certain application is strongly dependent on the exact liquid crystalline phase, the temperature range of the phase and the molecular structure. We therefore seek to synthesize and characterize novel tailor-made liquid crystals for selected applications.
Characterization of the liquid crystalline properties is done via polarizing optical microscopy, differential scanning calorimetry and X-ray spectroscopy.
[1] T. Wöhrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Chem. Rev. 2016, 116, 1139–1241.
[2] Link (Merck) (30.11.2020).
[3] M. Kumar, S. Kumar, Polym. J. 2017, 49, 85–111.
[4] H. Iino, T. Usui, J. Hanna, Nat. Commun. 2015, 6, 6828.
[5] H.-W. Chen, J.-H. Lee, B.-Y. Lin, S. Chen, S.-T. Wu, Light Sci. Appl. 2018, 7, 17168–17168.
Soluble Chitin [Sebastian Wachsmann]
Processability of chitin in the context of ChitinFluid.
Chitin is the second most common biopolymer.[10] It offers promising mechanical properties and is a waste product in various industrial processes like the production of ascorbic acid.[11] Besides the primary molecular structure, chitin has several superstructures which impede the splitting and desolvation of the material. Previous research used ionic liquids salts with a melting point below 100 °C to dissolve chitin by means of their high polar interactions and, thus, make it processable.[12] Within the ChitinFluid project, ionic liquid crystals ILCs are to be used as complex solvents. Tailor-made ILCs will be synthesized and characterized to investigate the solvation behavior of chitin/-derivatives.
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[10] M. V. Tracey, Pure Appl. Chem. 1957, 7, 1.
[11] D. B. Archer, I. F. Connerton, D. A. MacKenzie, in Food Biotechnol. (Eds.: U. Stahl, U.E.B. Donalies, E. Nevoigt), Springer, Berlin, Heidelberg, 2008, pp. 99–147.
[12] G. A. F. Roberts, Chitin Chemistry, Macmillan International Higher Education, 1992.
Liquid Crystals based on Polycyclic Aromatic Hydrocarbons [Falk Feucht]
Polycyclic aromatic hydrocarbons (PAHs) and heteroatom containing PAH derivatives often show interesting photophysical properties like absorption of visible light and fluorescence due to their large π-system.[1] Their rather flat structure makes them suitable as core motif for the synthesis of liquid crystals.[2] By functionalization with different substituents, the mesomorphic- and photophysical properties can be tuned. Addition of ionic headgroups and variation of the anion type and size can also have a great influence on these properties.[3,4] We aim to synthesize novel fluorescent neutral and ionic liquid crystals and characterize them according to their liquid crystalline and photophysical properties to get detailed insights on the structure to property relations of these functional materials.
[1] K. Bader, A. Baro, P. Ehni, W. Frey, R. Gündemir, S. Laschat, Y. Molard, Cryst. Growth Des. 2019, 19, 4436–4452.
[2] D. Demus, J. Goodby, G. W. Gray, H. W. Spiess, V. Vill, Handbook of Liquid Crystals, Wiley-VCH, Weinheim, 1998.
[3] M. Butschies, S. Sauer, E. Kessler, H.-U. Siehl, B. Claasen, P. Fischer, W. Frey, S. Laschat, ChemPhysChem 2010, 11, 3752–3765.
[4] M. Butschies, W. Frey, S. Laschat, Chem. – Eur. J. 2012, 18, 3014–3022.
Ionic liquids and ionic liquid crystals as tailor-made complex solvents [Michael Müller]
Ionic liquid crystals and ionic liquids are increasingly used as solvents in chemical reactions. Due to their high boiling points and low vapour pressure as well as their tailor-made properties, their use as solvents optimizes reactions. [1] [2]These solvents, however, are often based on expensive fine chemicals, which lead to great expenses.[3] Therefore, we aim to produce ILCs based on less expensive renewable resources, which are easy to synthesize and recycle.
[1] T. Welton, Coordination chemistry reviews 2004, 248, 2459-2477.
[2] A. K. Chakraborti, S. R. Roy, Journal of the American Chemical Society 2009, 131, 6902–6903.
[3] N. V. Plechkova, K. R. Seddon, Chemical Society Reviews 2008, 37, 123–150.
Amino-acid based Lyotropic Ionic Liquid Crystals [Soeren Bauch]
One important property of liquid crystals is the structural similarity with biological molecules, for example lipids or DNA. Especially lyotropic liquid crystals, which are solvent dependent, can therefore be used in drug delivery.[1,2] Ionic moieties within the molecule yield in ion conductivity and dissolving features.[3,4] In order to achieve both biological resemblance and ionic properties, amino-acids are suitable scaffolds.
[1] I. Dierking, A. Martins Figueiredo Neto, Crystals 2020, 10, 604.
[2] D.-H. Kim, A. Jahn, S.-J. Cho, J. S. Kim, M.-H. Ki, D.-D. Kim, J. Pharm. Investig. 2015, 45, 1–11.
[3] K. V. Axenov, S. Laschat, Materials 2011, 4, 206–259.
[4] N. Kapernaum, A. Lange, M. Ebert, M. A. Grunwald, C. Haege, S. Marino, A. Zens, A. Taubert, F. Giesselmann, S. Laschat, ChemPlusChem 2021, 87, e20210039.
Liquid Crystals as Basis for Hybrid Materials [Aileen Raab]
Due to their combined fluidity and functionality, liquid crystals have attracted attention in a widening array of commercial areas and research endeavors, such as optoelectronics, construction materials and medicinal applications, over the last fifty years. In this project, we aim to prepare liquid crystals based on a variety of organic compounds, including amino acids and dyes, for the development of novel functional hybrid materials. Through this, we intend to gain a deeper understanding of the behavior of liquid crystals in confined structures and hope to further broaden the scope of possible applications for liquid crystalline materials in the future.
Tetracoordinated Boron Containing Liquid Crystals [Franziska Müller]
Organic boron compounds have emerged as an attractive class of materials for the application in the field of optoelectronics. Especially tetracoordinated boron-chelates are a promising motif for this application due to their photophysical properties such as strong emission or TADF (thermally activated delayed fluorescence).[1,2] This type of boron-complex is built with donor ligands, for which nitrogen- or oxygen-based building blocks are particularly suitable. While tetracoordinated boron compounds are quite well investigated in terms of the photophysics, the combination of those properties with mesomorphic behavior is studied less.[3] We aim to create novel fluorescent liquid crystalline materials based on tetracoordinated boron atoms and tune them regarding the emission and mesomorphic properties.
[1] Y.-J. Shiu, Y.-T. Chen, W.-K. Lee, C.-C. Wu, T.-C. Lin, S.-H. Liu, P.-T. Chou, C.-W. Lu, I.-C. Cheng, Y.-J. Lien, Y. Chi, J. Mater. Chem. C 2017, 5, 1452–1462.
[2] A. Pershin, D. Hall, V. Lemaur, J.-C. Sancho-Garcia, L. Muccioli, E. Zysman-Colman, D. Beljonne, Y. Olivier, Nat Commun 2019, 10, 597.
[3] Y.-W. Chen, G.-H. Lee, C. K. Lai, Dalton Trans. 2017, 46, 12274–12283.
Azobenzene-based Liquid Crystals [Daniel Rück]
Azobenzene is an organic compound characterized by its distinctive nitrogen-nitrogen double bond linking two phenyl groups. It exhibits unique photoresponsive properties, meaning it can undergo reversible isomerization between its trans and cis forms upon exposure to light.[1,2] The photoisomerization depends on the electronic system and the respective substituents of the azobenzene core. This mechanism provides numerous advantages regarding possible applications in molecular devices and functional materials. The photoswitching abilities enables an additional element of control besides temperature, when the azobenzene core is incorporated in the design of liquid crystals.[3,4] Therefore, we strive towards the synthesis and characterization of novel azobenzene-based liquid crystals regarding their mesomorphic and photophysical behaviour in bulk and confinement.
[1] H. M. Dhammika Bandara, S. C. Burdette, Chem. Soc. Rev. 2012, 41, 1809–1825.
[2] M. Gao, D. Kwaria, Y. Norikane, Y. Yue, Nat. Sci. 2023, 3, e220020.
[3] E. Wuckert, M. D. Harjung, N. Kapernaum, C. Mueller, W. Frey, A. Baro, F. Giesselmann, S. Laschat, Phys. Chem. Chem. Phys. 2015, 17, 8382–8392.
[4] G. S. D. Santos, E. Westphal, New J. Chem. 2022, 46, 7334–7345.
Liquid Crystals based on Crown Ether Motifs [Sara Simonovska]
Liquid crystals (LCs) with a central crown ether (CE) motif are known to show columnar mesophase geometries granting access to the application field of OFETs and OLEDs.[1,2] Their ability to complex cations, particularly alkali metal cations, extends the scope significantly. While conventional salts often broaden or even induce mesophases,[3] this capability to form host guest complexes can also be exploited to process ceramic-like anionic metal clusters containing stabilizing cations[4] resulting in hybrid materials retaining liquid crystalline properties of the LC as well as emission properties of the clusters.[5,6] This inspired us to aim for other CE based LCs to design all kinds of hybrid materials thus further widening this research topic.
[1] S. Laschat, A. Baro, N. Steinke, F. Giesselmann, C. Hägele, G. Scalia, R. Judele, E. Kapatsina, A. Schreivogel, S. Sauer, M. Tosoni, Angew. Chem. 2007, 119, 4916-4973.
[2] T. Wöhrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Chem. Rev. 2016, 116, 1139–1241.
[3] S. Laschat, A. Baro, N. Steinke, F. Giesselmann, C. Hägele, G. Scalia, R. Judele, E. Kapatsina, S. Sauer, A. Schreivogel, M. Tosoni, Angew. Chem. Int. Ed. 2007, 46, 4832–4887.
[4] Y. Molard, Acc. Chem. Res. 2016, 49, 1514 – 1523.
[5] S. K. Nayak, M. Amela-Cortes, M. M. Neidhardt, S. Beardsworth, J. Kirres, M. Mansueto, S. Cordier, S. Laschat, Y. Molard, Chem. Commun. 2016, 52, 3127–3130.
[6] K. Guy, P. Ehni, S. Paofai, R. Forschner, C. Roiland, M. Amela-Cortes, S. Cordier, S. Laschat, Y. Molard, Angew. Chem. Int. Ed. 2018, 57, 11692–11696.