| As one of soft mesogenic architectures,liquid crystalline microstructure is a topic of high interest in functional photonic application due to its fascinating tunability of optical anisotropy,resulting from the rearrangement of molecular alignment by external stimuli.Based on skillful architecture,photo-and thermo-responsive liquid-crystalline systems have superior advantages of precise controllability in an uncontacted way and adaptation in surrounding environments,resulting in promising applications in information recorder,optic communication,bio-sensing and integrated optics.In this thesis,the design,synthesis,preparation and application of photo-and thermo-responsive cholesteric liquid-crystalline composites would be explored,to put emphasis on their optical properties and dynamic behaviors in response to external stimuli.The main research contents are listed as follows:(1)A series of chiral overcrowded alkenes(OAs)with structural modification on rotor part were judiciously designed and synthesized.Their chemical kinetic analysis were performed by transition state theory with Eyring equation in isotropic organic liquid and anisotropic achiral liquid crystal(LC)host,respectively.It is found that the existence of the rod-like substituent exhibits a relatively strong intermolecular interaction with the rod-shape LC molecules in the guest-host system,indicating a noticeable enlargement of structural entropy effect in the chemical dynamic isomerization motion,resulting in an increasingly larger difference in the chemical kinetics of OAs in different media.These results provide significant impetus toward the further structure design and characterization of OAs.(2)Photo-responsive cholesteric liquid crystal(ChLC)composites containing chiral OA/chiral compound/nematic LC were prepared.Upon UV irradiation and thermal treatment,the stimuli-directed dynamic reconfiguration of ChLCs can be achieved between the disorder helixes(focal conic texture)at the photostationary state(PSS)and the uniformly standing helixes(planar texture)at the thermostationary state(TSS).It is found that the reversible micromorphology deformation processes are compatible with the free energy fluctuation of ChLC composites and the chemical kinetics of chiral OAs under different conditions.Furthermore,stimuli-directed reversible one-dimensional beam steering based on OA-doped ChLCs can be achieved between ’on’ and ’off states by the photo-polymerized stripe lithography.Besides,by adjusting the photo-responsive ChLC composites to botain the increased pitch upon UV irradiation,light-driven dynamic homogeneous alignment of ChLC molecules can be achieved.(3)Single-layer photo-responsive ChLC composites containing chiral OA/nematic LC were prepared.Upon exposure to UV light with different intesites,reversible reflection bandgap in dynamic shifting,broadening and deepening can be achieved in one system.On the basis of the UV absorptivity and the UV-intensity dependence of photo-isomerization ratio of chiral OAs,the particular arrangement of helical pitch with chiral handedness inversion and the special optical performances can be obtained by the gradient distribution of UV intensity in the ChLCs,which can be evidently observed in liquid-crystalline polymer system.(4)Temperature-adaptive polymer-stabilized liquid crystal(PSLC)films with adjustable light transmittance containing liquid crystalline polymer network/Smectic A(SmA)-Cholesteric(Ch)LC were prepared.The thermo-optical characteristics with the contrast ratio and the switching speed have been investigated.It is found that the liquid crystalline polymer network with the planar alignment is the key point to botain the thermo-opticalt ransition between the light-scattering state within SmA phase at low temperature and the transparent state within Ch phase at high temperature.To tune the microscopic structure of polymer network in the PSLC films by the composites and the polymerized condiction,the contrast ratio and the switching speed can be optimized. |
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