845wileyonlinelibrary.com COMMUNICATION www.MaterialsViews.com www.advopticalmat.de coherent light sources in the fi eld of soft matter photonics. [8][9][10] Moreover, 3D photonic microstructures show promising potential to realize omnidirectional, narrow line-width and controllable emission, which may signifi cantly broaden the applications of CLC band edge lasers. [ 11 ] However, 3D lasing involving CLCs has not been much explored, [ 10,11 ] and there is no report on lasing using photoresponsive cholesteric microshells. Recently, a microfl uidics-based method has been reported to generate CLC spherical shells that can serve as 3D photonic crystals for omnidirectional laser emission owing to the radial arrangement of helical axes within the cholesteric shells. [ 12 ] However, the band edge laser emission only occurs at a fi xed wavelength.Here we report a straightforward approach to fabricate photoresponsive CLC spherical microshells composed of the new visible light-driven chiral molecular switch ( R )-1 ( Figure 1 ) and the commercially available fl uorescent dye and LC. [ 13 ] The resulting microshells are monodisperse and can generate LC lasers with phototunable output wavelength. The photoisomerization of the light-driven switch molecules enables us to shift the wavelength of the LC laser by optical pumping, and fully recover the laser wavelength by keeping the sample in the dark. To the best of our knowledge, this is the fi rst report on photoresponsive liquid crystalline microshells. It is also the fi rst demonstration of a phototunable LC laser in the form of spherical CLC microshells, which is based on an interesting "pumpingself-tuning" mechanism.The new visible light-driven chiral molecular switch ( R )-1 was prepared by a facile synthesis, and its chemical structure was well-identifi ed by 1 H and 13 C NMR spectroscopy, and highresolution mass spectrometry (see Supporting Information). It was chemically and thermally stable, and showed optically tunable behavior in both organic solvent and LC media. The chiral switch ( R )-1 exhibited a very high helical twisting power of 198 µm −1 at the initial state in an achiral LC E7, which decreased to 175 µm −1 upon irradiation with 530 nm light. As expected, doping it in E7 even at a low concentration can induce an optically tunable helical superstructure. The PBG of the CLC with 5.0 wt% ( R )-1 initially appears in the visible light region with the central wavelength around 550 nm ( Figure S4). Upon irradiation with 530 nm light, the PBG shows a red-shift; fi nally at the photostationary state (PSS), the central wavelength of the PBG moves to 630 nm. The phototuning of PBG is the underlying mechanism for the potential laser tunability of this cholesteric material as the absorption of the chiral dopant overlaps with the wavelength of the pumping laser. We also observed a slight red-shift of ca. 10 nm in the refl ection when 0.5 wt% Bottom-up fabrication of 3D photonic structures with unique optical properties is currently a burgeoning area of research. In thi...
The quest for interesting properties and phenomena in liquid crystals toward their employment in nondisplay application is an intense and vibrant endeavor. Remarkable progress has recently been achieved with regard to liquid crystals in curved confined geometries, typically represented as enclosed spherical geometries and cylindrical geometries with an infinitely extended axial-symmetrical space. Liquid-crystal emulsion droplets and fibers are intriguing examples from these fields and have attracted considerable attention. It is especially noteworthy that the rapid development of microfluidics brings about new capabilities to generate complex soft microstructures composed of both thermotropic and lyotropic liquid crystals. This review attempts to outline the recent developments related to the liquid crystals in curved confined geometries by focusing on microfluidics-mediated approaches. We highlight a wealth of novel photonic applications and beyond and also offer perspectives on the challenges, opportunities, and new directions for future development in this emerging research area.
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