Liquid Crystals and Functional Materials

Overview of liquid crystal topics covered by the Laschat Research Group

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. 

Azulene [Finn Schulz]

Azulene fascinates many scientists due to its blue color despite of its small π-system.[6] It consists of a five- and a seven-membered ring and is isomeric to naphthalene. A zwitterionic resonance structure fulfills Hückel's rule for both rings and explains the rather stronger dipole moment of 1.08 D. The non-alternant character of this unique molecule was exploited in optoelectronic materials.[7,8] We aim to combine the self-assembly of liquid crystals with the unique electronic properties of colorful azulene for development of new high-performance materials.[9]

[6] R. S. H. Liu, J. Chem. Educ. 2002, 79, 183.
[7] Q. Fan, D. Martin-Jimenez, D. Ebeling, C. K. Krug, L. Brechmann, C. Kohlmeyer, G. Hilt, W. Hieringer, A. Schirmeisen, J. M. Gottfried, J. Am. Chem. Soc. 2019, 141, 17713–17720. 
[8] H. Xin, X. Gao, ChemPlusChem 2017, 82, 945–956. 
[9] F. Schulz, P. Ehni, B. Wank, A. Bauer, W. Frey, S. Laschat, Liq. Cryst. 2020, DOI 10.1080/02678292.2020.1821919.

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.

[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.

B,N‑ and B,O- Polycyclic Aromatic Hydrocarbons [Julius Knöller]

Polycyclic aromatic hydrocarbons (PAHs) are a vast class of functional materials. Their extended π‑system renders them with unique properties such as electrical conductivity, absorption of visible light and strong fluorescence. An important setscrew to influence the electronic properties of such PAHs is the replacement of one or several carbon atoms in the aromatic backbone with other main group elements (the so-called heteroatom doping).[13–16] Recently, Boron doped PAHs have emerged from inorganic curiosities to an important class of functional materials especially present in Organic Light Emitting Diode (OLED) research.[17–20] While Boron doped PAHs (B‑PAHs) are a quite well investigated class of compounds, their self-assembly remains to be addressed with only two examples of liquid crystalline B‑PAHs being known.[21,22] We aim to create novel, self-assembling B,N- and B,O‑PAHs tailored for application in OLEDs.[23]

[13] M. Hirai, N. Tanaka, M. Sakai, S. Yamaguchi, Chem. Rev. 2019, 119, 8291–8331.
[14] T. A. Schaub, K. Padberg, M. Kivala, J. Phys. Org. Chem. 2020, 33, 1–27.
[15] E. von Grotthuss, A. John, T. Kaese, M. Wagner, Asian J. Org. Chem. 2018, 7, 37–53.
[16] S. K. Mellerup, S. Wang, Trends Chem. 2019, 1, 77–89.
[17] T. Hatakeyama, K. Shiren, K. Nakajima, S. Nomura, S. Nakatsuka, K. Kinoshita, J. Ni, Y. Ono, T. Ikuta, Adv. Mater. 2016, 28, 2777–2781.
[18] N. Ikeda, S. Oda, R. Matsumoto, M. Yoshioka, D. Fukushima, K. Yoshiura, N. Yasuda, T. Hatakeyama, Adv. Mater. 2020, 2004072, 2004072.
[19] Y. Kondo, K. Yoshiura, S. Kitera, H. Nishi, S. Oda, H. Gotoh, Y. Sasada, M. Yanai, T. Hatakeyama, Nat. Photonics 2019, 13, 678–682.
[20] S. Madayanad Suresh, D. Hall, D. Beljonne, Y. Olivier, E. Zysman‐Colman, Adv. Funct. Mater. 2020, 1908677, 1908677.
[21] T. Kushida, A. Shuto, M. Yoshio, T. Kato, S. Yamaguchi, Angew. Chem. Int. Ed. 2015, 54, 6922–6925.
[22] B. Adelizzi, P. Chidchob, N. Tanaka, B. A. G. Lamers, S. C. J. Meskers, S. Ogi, A. R. A. Palmans, S. Yamaguchi, E. W. Meijer, J. Am. Chem. Soc. 2020, DOI 10.1021/jacs.0c06921.
[23] J. A. Knöller, G. Meng, X. Wang, D. Hall, A. Pershin, D. Beljonne, Y. Olivier, S. Laschat, E. Zysman‐Colman, S. Wang, Angewandte Chemie 2020, 132, 3181–3185.

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.

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