Bandwidth-tunable anisotropic spatial light modulators are fabricated with redox-responsive dichroic mesogens. By introducing an ionic group and a polymerizable group into the chromophore, the programmed reactive mesogen (PDI-MA) exhibits a lyotropic chromonic liquid crystal (LCLC) phase. The PDI-MA molecule forms a stable aromatic dianion state so that the absorption wavelengths of the dichroic mesogen can be reversibly tuned by redox reactions. Through a continuous process of coating, molecular self-assembly, and polymerization, redoxresponsive and uniaxially oriented LCLC polymer films are fabricated. Because of the high dichroic ratio of PDI-MA, the uniaxially oriented LCLC network is capable of anisotropic light modulation in the visible-light spectrum. Uniaxially oriented LCLC films are applied to flexible multichromic smart windows and optical security filters for anticounterfeiting.
The development of a shape memory
polymer (SMP) with high thermal
conductivity should precede the fabrication of fast-responsive soft
thermoactuators because the effective heat transfer in thermoactuators
expedites the shape-morphing process. A tetrathiafulvalene (TTF)-based
monomer (TTF-SH) containing four flexible chains and thiol reactive
functions is newly designed and synthesized for the development of
SMP with excellent thermal conductivity. Thanks to the thermally induced
chemical bond formation of TTF-SH from thiol to disulfide, TTF-based
SMP is simply prepared without the addition of any catalyst or initiator.
The TTF SMP exhibits not only high thermal conductivity (1.12 W/(m
K)) but also high fixing and recovery ratios (99.42 and 99.98%). The
correlation between heat transfer and shape-morphing speed of the
TTF SMP is established by examining shape memory characteristics over
time. The TTF SMP shows a fast shape-morphing response due to its
excellent thermal conductivity. With the newly developed TTF SMP thermoactuator,
we demonstrate a warning sensor to alarm the device overheating as
well as a smart sunshade to automatically cut off solar energy.
Many studies on the basis of cholesteric liquid crystal (CLC) have focused on dynamic optical changes utilizing photochemical reactions raising helical pitch variations. However, the conventional dyes doped in CLC system often show reversible isomerization such as trans‐cis, E‐Z, and open‐close forms that hampers the fixation of desired color cues. Here, a cyanostilbene‐based reactive mesogen (CSRM) for phototunable and subsequently polymerizable smart CLC paints is newly designed and synthesized. The structural color of the CLC paint can be precisely manipulated in remote controllable manner by inducing a photochemical reaction of CSRM. Due to the irreversible isomerization behaviors of CSRM, the constructed periodic structures with different helical pitches are intactly fixed via in situ photopolymerization under 460 nm light. In addition, the combination of helical nanostructures and cyanostilbene luminophore produces a circularly polarized light emission. The dissymmetry factor of circularly polarized luminescence is dependent on the photoregulated helical nanostructures in CLC films. The decoupled system of triple photofunctionality in a single component of chirophotonic crystalline material is applied to develop advanced optical information storages.
An anisotropic light emitting metallomesogen (PtM) consisting of a cyclometalated platinum(II)-terpyridine (Pt(II)-tpy) chromophore and a flexible dendron is newly synthesized as a thermal-induced and polarization-induced solid-state luminescence switching material. The self-assembled PtM is uniaxially aligned by mechanical shearing within the mesophase resulting in high optical anisotropy with chromophores. The shear-induced metastable PtM crystal exhibits emission change depending on the polarization direction and thermally triggered reversible emission quenching-recovery characteristic. In order to precisely control the optical feature of the PtM, the self-assembled supramolecular structure and thermal-sensitive photophysical properties are characterized. Based on the multiresponsive luminescence switching system of PtM, a multiplexed optical code is encrypted with a simple coating and its feasibility for optical anticounterfeiting applications is demonstrated.
Stimuli-responsive liquid crystal polymer networks (LCPNs) consisting of azobenzene are mostly studied based on ultraviolet (UV)-induced photochemical isomerization. However, depending on the molecular structure and the degree of UV absorption of azobenzene molecules, the photothermal effect can induce stimuli-responsiveness of azobenzene-based LCPN. In this report, an azobenzene-based monoacrylate (AM) monomer that can be easily introduced into an LCPN is designed and synthesized to develop a multifunctional LCPN that exhibits a photothermal effect. An AM LCPN is successfully fabricated with AM, LC monomer, and thiol groups, and the fabricating process is systematically optimized by controlling the ratio of each component. The thermal, mechanical, and structural behaviors of the AM LCPN are confirmed through various experimental analyses, and the shape memory properties are quantitatively and qualitatively verified via dynamic mechanical analysis and photographs. Thanks to the azobenzene molecules present, the AM LCPN exhibits a photothermal effect under UV exposure, which is demonstrated by macroscopic and spectroscopic experiments. Alignment and self-healing experiments indicate that the AM LCPN can be applied to fields requiring orientation or self-healing property.
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