Liquid Crystals

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 of 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 impedes 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- Polycylcic 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.

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