We investigate the influence of the host matrix on the photothermally driven actuation performance of negatively photochromic, donor–acceptor Stenhouse adduct (DASA)-based polymers. Using a modular Diels–Alder “click” platform, we designed polymeric materials with varying DASA incorporation and investigated the relationships between the material composition and the resulting physical, mechanical, and photoswitching properties. We demonstrate that increasing the DASA concentration in polymer conjugates has a dramatic effect on the material’s physical and mechanical properties, such as the glass transition temperature (T g) and elastic modulus, as well as the photoswitching properties, which are found to be highly dependent on T g. We establish using a simple photoresponsive bilayer that actuation performance is controlled by the bilayer stiffness rather than the photochrome incorporation of DASA. Finally, we report and compare the light-induced property changes in T g and the elastic modulus between the materials comprising the open or closed forms of DASAs. Our results demonstrate the importance of designing a material that is stiff enough to provide the mechanical strength required for actuation under load, but soft enough to reversibly switch at the operational temperature and provide key considerations for the development of application-geared photoswitchable materials.

A triphenylene-based reactive mesogenic molecule (abbreviated as HABET) was newly designed and synthesized as a programmed building block to construct the striped walls by the photopolymerization in the anisotropic liquid crystal (LC) solvents. On the basis of thermal, scattering and microscopic analyses, it was found that HABET formed three ordered structures: a columnar hexagonal LC phase (Φ H ), a tilted columnar hexagonal LC phase (Φ T ) and a highly ordered columnar oblique crystal phase (Φ OK ). The microscopic molecular orientations in the hierarchical superstructures were controlled in the anisotropic LC solvents with the help of surface anchoring forces, while the dimensions of the striped wall morphologies were determined by the patterned photomasks. The long axis of self-assembled columns in the striped walls was perpendicular to the surface alignment direction regardless of the photomask direction. Additionally, it was realized that the shapes of water drops as well as the surface water contact angles can be tuned by the hierarchical superstructures and morphologies of the polymerized HABET networks. The anisotropic hierarchical superstructures and morphologies concurrently fabricated during the polymerization in the anisotropic LC medium can offer a potential pathway for liquid transportation in the microfluidic devices.

The well-defined hierarchical superstructures constructed by the self-assembly of programmed supramolecules can be organized for the fabrication of remote-controllable actuating and rewritable films. To realize this concept, we newly designed and synthesized a benzene-1,3,5-tricarboxamide (BTA) derivative (abbreviated as BTA-3AZO) containing photoresponsive azobenzene (AZO) mesogens on the periphery of the BTA core. BTA-3AZO was first self-assembled to nanocolumns mainly driven by the intermolecular hydrogen-bonds between BTA cores, and these self-assembled nanocolumns were further self-organized laterally to form the low-ordered hexagonal columnar liquid crystal (LC) phase below the isotropization temperature. Upon cooling, a lamello-columnar crystal phase emerged at room temperature via a highly ordered lamello-columnar LC phase. The three-dimensional (3D) organogel networks consisted of fibrous and lamellar superstructures were fabricated in the BTA-3AZO cyclohexane-methanol solutions. By tuning the wavelength of light, the shape and color of the 3D networked thin films were remote-controlled by the conformational changes of azobenzene moieties in the BTA-3AZO. The demonstrations of remote-controllable 3D actuating and rewritable films with the self-assembled hierarchical BTA-3AZO thin films can be stepping stones for the advanced flexible optoelectronic devices.

For the development of advanced heat transfer organic materials (HTOMs) with excellent thermal conductivities, triphenylene-based reactive discogens, 2,3,6,7,10,11-hexakis(but-3-enyloxy)triphenylene (HABET) and 4,4',4″,4‴,4'''',4'''''-(triphenylene-2,3,6,7,10,11-hexaylhexakis(oxy))hexakis(butane-1-thiol) (THBT), were synthesized as discotic liquid crystal (DLC) monomers and cross-linkers, respectively. A temperature-composition phase diagram of HABET-THBT mixtures was first established based on their thermal and microscopic analyses. From the experimental results, it was realized that the thermal conductivity of DLC HTOM was strongly affected by the molecular organizations on a macroscopic length scale. Macroscopic orientation of self-assembled columns in DLC HTOMs was effectively achieved under the rotating magnetic fields and successfully stabilized by the photopolymerization. The DLC HTOM polymer-stabilized at the LC phase exhibited the remarkable thermal conductivity above 1 W/mK. When the DLC HTOM was macroscopically oriented, the thermal conductivity was estimated to be 3 W/mK along the in-plane direction of DLC molecule. The outstanding thermal conductivity of DLC HTOM should be originated not only from the high content of two-dimensional aromatic discogens but also from the macroscopically oriented and self-assembled DLC. The newly developed DLC HTOM with an outstanding thermal conductivity as well as with an excellent mechanical sustainability can be applied as directional heat dissipating materials in electronic and display devices.

To develop an advanced heat transfer composite, a deeper understanding of the interfacial correlation between matrix and filler is of paramount importance. To verify the effect of interfacial correlations on the thermal conductivity, the conductive fillers such as expanded graphite (EG) and boron nitride (BN) are introduced in the discotic liquid crystal (DLC)-based polymeric matrix. The DLC matrix exhibits better interfacial affinity with EG compared to BN because of the strong π-π interactions between EG and DLC. Thanks to its excellent interfacial affinity, the EG-DLC composites show a synergistic increment in thermal conducting performance.

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.

A programed light‐responsive chiral liquid crystal (LC) containing four photochromic azobenzene moieties covalently connected to a central bicyclic chiral core (abbreviated as AZ4ICD) is newly designed, precisely synthesized, and efficiently applied as a remote‐controllable molecular knob for the optically tunable thin film. First of all, phase evolutions and ordered structures of AZ4ICD are systematically investigated by a combination of thermal, microscopic, scattering, and simulation techniques. Wide‐angle X‐ray diffractions of oriented AZ4ICD samples indicate that the AZ4ICD molecule itself basically forms layer structures: one is a low‐ordered chiral smectic A LC phase (SmA*) with 5.61 nm layer periodicity at high temperatures, and two highly ordered smectic crystal (SmCr1 and SmCr2) phases are subsequently formed at lower temperatures with the anticlinically tilted molecular packing structures. The helical superstructures of chiral nematic LC phase (N*) can be spontaneously constructed by doping AZ4ICD chiral agents into the achiral nematic molecules. Due to the bent conformational geometry of AZ4ICD, the thermal window of blue LC phase (BP) is expanded by stabilizing the double twisted cylindrical building blocks. Remote‐controllable phase transformations in the mesomorphic helical superstructures are demonstrated by tuning the wavelength of light.

Without the conventional polymer-based liquid crystal (LC) alignment process, a newly synthesized dual photo-functionalized amphiphile (abbreviated as ADMA1 ) was successfully applied as a robust photo-reversible LC alignment layer by self-assembly and photo-polymerization. The LC alignment layer constructed by directly adding dual photo-functionalized amphiphiles into LC media significantly cuts the manufacturing cost as well as opens new doors for the fabrication of novel electro-optical devices.