Professor Huai Yang’s group in College of Engineering at Peking University has made a series of new progress in liquid crystalline functional materials and the fields recently. The specific contents are as follows:
(1) A single-layer liquid crystalline elastomer (LCE) film showing dual responsiveness to humidity and SO2 gas is prepared by optical polymerization of the liquid crystalline carboxylic acid dimers. The humidity-sensitivity of the LCE film can be gated by exposing the film to SO2. Based on the functional materials, the dual-response to humidity and acid gas of natural flowers was roughly mirrored, which renders the LCE film valuable in design and preparation of multifunctional devices. This work was published on the Adv. Funct. Mater. (DOI：10.1002/adfm.201900013), of which Prof. Huai Yang is the corresponding author, and Ruochen Lan, doctoral candidate at Peking University, is the first author.
Figure 1. Schematic illustration and photograph of the SO2-gated humidity responsive motion of the artificial flower
(2) A chiral thiol with a high helical twisting power was synthesized through an ingenious synthetic route with high selectivity, yield and cost-effectiveness, which was first used to fabricate a liquid crystal composite film with ultra-wide broadband reflection via thiol-click chemistry. Compared with the cholesteric liquid crystal film based on acrylate system, the film has wider reflection bandwidth under the same preparation conditions and the waveband can be precisely regulated. This film with broadband reflection has many potential applications for broadband polarizers, polarizer-free displays, organic optical data storage media, smart switchable reflective windows, continuous waveband laser protection and brightness enhancement films for LCD. This work was published in Angew. Chem. Int. Ed. (DOI：10.1002/anie.201902681), of which Prof. Huai Yang is the corresponding author, and Wei Hu, a doctoral candidate at Beijing university of science and technology, is the first author.
Figure 2. Polymer stabilized cholesteric liquid crystal film with broadband reflection：(a) Schematic mechanism；(b)SEM images of pitch gradient distribution；(c) EDS Mapping of O gradient distribution；(d) EDS Mapping of S gradient distribution；(e) Reflectance bandwidth broaden with the photopolymerization time，the maximum bandwidth exceeds 2000 nm
(3) By cooperating with Prof. Shaojun Guo, Prof. Huai Yang and his cooperators promoted silica-passivated perovskite quantum dots (SP-PQDs) possessing highly compatibility with polar medium by in situ hydrolyzing the surface ligands of (3-aminopropyl) triethoxysilane. Furthermore, florescent microspheres were also prepared based on the promoted SP-PQDs via a swelling-deswelling method in polar solvents. This work may open new avenues for greener synthesis, scalable production, and long-term storage of perovskite quantum dots (PQDs) towards the emerging practical applications, and provides new insights for further studies of liquid crystals / quantum dots composites. The related work was published in the journal of Angew. Chem. Int. Ed. (2019, 58(9), 2799-2803), of which Prof. Huai Yang and Prof. Shaojun Guo were the co-corresponding authors, and the first author was Xiao Liang, a PhD candidate from Peking University.
Figure 3. (a) Schematic illustration of the preparation of the SP-PQDs. (b~e) Photographs of the SP-PQDs flocculated by a polar solvent and separated by a low-speed centrifugation. (f~k) Schematic illustration of the fabrication of florescent microspheres via a swelling-deswelling process to realize the long-term storage and re-usage of SP-PQDs. (l) TEM images and (m) florescent photographs of the as-made SP-PQDs. (n) Variations of the quantum yields for the florescent microspheres and the bared traditional PQDs under ambient conditions
(4) By cooperating with Prof. Guirong Xiong, Prof. Huai Yang and his cooperators prepared microstripes with arbitrary electrical conductivity through incorporating discotic liquid crystals (DLCs) with molecular motors. The conductivity of the microstripes could be continuously modulated by 365 nm UV light due to the influence of molecular motion under UV irradiation on the electron orbital overlap of columnar nanostructures. Moreover, the device shows memory effect and reversible conductivity change. The DLC microstripe arrays are very promising for the applications in UV detectors, memory devices, optical switches. This work is published on the Adv. Mater. (DOI: 10.1002/adma.201806016). Prof. Huai Yang and Dr. Guirong Xiong are co-corresponding authors, Dr. Chen Zou and post-doctor Jian Sun at Peking University are co-first authors.
Figure 4. Chart of the influence of configuration change of molecular motor on the DLC microstripes and the J-V curves of microstripes under different intensity of UV irradiation
(5) By cooperating with Prof. Guirong Xiong, Prof. Huai Yang and his cooperators prepared uniform aligned single crystal microstripes of terthiophene (TTP) smectic liquid crystals through a dewetting strategy. Microstripes prepared below crystalline temperature are uniform, well-ordered, and show high field effect transistor (FET) mobility. This strategy promised to provide a new opportunity for the high cost-efficiency fabrication of OFETs. This work is published on Adv. Funct. Mater. (DOI: 10.1002/adfm.201804838). Prof. Huai Yang and Dr. Guirong Xiong are co-corresponding authors, Dr. Chen Zou from Peking University and Naoto Yanahashi, a PhD candidate from Chuo University, are co-first authors.
Figure 5. Schematic showing the possible alignment process of TTP smectic liquid crystal in different phase and the corresponding transfer characteristic curves
The work above was jointly supported by the National Natural Science Foundation of China and the National Key R&D Program of China.