Photochemically and Thermally Programmed Optical Multi-States from a Single Diacetylene-Functionalized Cyanostilbene Luminogen.

To develop advanced optical systems, many scientists have endeavored to create smart optical materials which can tune their photophysical properties by changing molecular states. However, optical multi-states are obtained usually by mixing many dyes or stacking multi-layered structures. Here, multiple molecular states are tried to be generated with a single dye. In order to achieve the goal, a diacetylene-functionalized cyanostilbene luminogen (DACSM) is newly synthesized by covalently connecting diacetylene and cyanostilbene molecular functions. Photochemical reaction of cyanostilbene and topochemical polymerization of diacetylene can change the molecular state of DACSM. By thermal stimulations and the photochemical reaction, the conformation of polymerized DACSM is further tuned. The synergetic molecular cooperation of cyanostilbene and diacetylene generates multiple molecular states of DACSM. Utilizing the optical multi-states achieved from the newly developed DACSM, switchable optical patterns and smart secret codes are successfully demonstrated.

White light thermoplasmonic activated gold nanorod arrays enable the photo-thermal disinfection of medical tools from bacterial contamination.

The outspread of bacterial pathogens causing severe infections and spreading rapidly, especially among hospitalized patients, is worrying and represents a global public health issue. Current disinfection techniques are becoming insufficient to counteract the spread of these pathogens because they carry multiple antibiotic-resistance genes. For this reason, a constant need exists for new technological solutions that rely on physical methods rather than chemicals. Nanotechnology support provides novel and unexplored opportunities to boost groundbreaking, next-gen solutions. With the help of plasmonic-assisted nanomaterials, we present and discuss our findings in innovative bacterial disinfection techniques. Gold nanorods (AuNRs) immobilized on rigid substrates are utilized as efficient white light-to-heat transducers (thermoplasmonic effect) for photo-thermal (PT) disinfection. The resulting AuNRs array shows a high sensitivity change in refractive index and an extraordinary capability in converting white light to heat, producing a temperature change greater than 50 °C in a few minute interval illumination time. Results were validated using a theoretical approach based on a diffusive heat transfer model. Experiments performed with a strain of Escherichia coli as a model microorganism confirm the excellent capability of the AuNRs array to reduce the bacteria viability upon white light illumination. Conversely, the E. coli cells remain viable without white light illumination, which also confirms the lack of intrinsic toxicity of the AuNRs array. The PT transduction capability of the AuNRs array is utilized to produce white light heating of medical tools used during surgical treatments, generating a temperature increase that can be controlled and is suitable for disinfection. Our findings are pioneering a new opportunity for healthcare facilities since the reported methodology allows non-hazardous disinfection of medical devices by simply employing a conventional white light lamp.

When Chirophotonic Film Meets Wrinkles: Viewing Angle Independent Corrugated Photonic Crystal Paper.

Light manipulation strategies of nature have fascinated humans for centuries. In particular, structural colors are of considerable interest due to their ability to control the interaction between light and matter. Here, wrinkled photonic crystal papers (PCPs) are fabricated to demonstrate the consistent reflection of colors regardless of viewing angles. The nanoscale molecular self-assembly of a cholesteric liquid crystal (CLC) with a microscale corrugated surface is combined. Fully polymerizable CLC paints are uniaxially coated onto a wrinkled interpenetrating polymer network (IPN) substrate. Photopolymerization of the helicoidal nanostructures results in a flexible and free-standing PCP. The facile method of fabricating the wrinkled PCPs provides a scalable route for the development of novel chirophotonic materials with precisely controlled helical pitch and curvature dimensions. The reflection notch position of the flat PCP shifts to a lower wavelength when the viewing angle increased, while the selective reflection wavelength of wrinkled PCP is remained consistent regardless of viewing angles. The optical reflection of the 1D stripe-wrinkled PCP is dependent on the wrinkle direction. PCPs with different corrugated directions can be patterned to reduce the angular-dependent optical reflection of wrinkles. Furthermore, 2D wavy-wrinkled PCP is successfully developed that exhibit directionally independent reflection of color.

Remote-controllable and encryptable smart glasses: a photoresponsive azobenzene molecular commander determines the molecular alignments of liquid crystal soldiers.

For the development of optically encryptable smart glass that can control the molecular alignment of liquid crystals (LCs), an azobenzene-based reactive molecule (ARM) capable of trans-cis photoisomerization is newly designed and synthesized. Photo-triggered LC-commandable smart glasses are successfully constructed by the surface functionalization technique using 3-aminopropyltriethoxysilane (APTMS) coupling agent and an ARM. The surface functionalization with the ARM is verified by spectroscopic analysis and various observations including changes in the wettability and surface morphology. Using the ARM-treated substrate, the LC command cell which can effectively switch the molecular orientation of nematic LC (E7) by the irradiation of UV and visible light is demonstrated. The results of optical investigation demonstrate the directional correlation between light and photoisomerization, revealing the tilt mechanism of azobenzene units. The capability to control the molecular orientation of LCs remotely and selectively allows the development of remote-controllable and encryptable smart glasses.

The transfer and amplification of cyanostilbene molecular function to advanced flexible optical paints through self-crosslinkable side-chain liquid crystal polysiloxanes.

A self-crosslinkable side-chain liquid crystal polysiloxane containing cyanostilbene (Si-CSM) was newly synthesized for the development of a new generation of flexible optical paints. The photoisomerization of the cyanostilbene moiety at the molecular level was transferred and amplified to the phase transition of Si-CSM, resulting in changes in the macroscopic optical properties of the Si-CSM thin film. The self-crosslinking reaction between Si-H groups in the Si-CSM polymer backbone caused the self-crosslinked Si-CSM thin film to be very elastic and both thermally and chemically stable. Therefore, the self-crosslinked Si-CSM thin film endured stretching and bending deformations under relatively harsh conditions. In addition, the uniaxially oriented and self-crosslinked Si-CSM thin film generated linearly polarized light emission. Polarization-dependent and photopatternable secret coatings were fabricated via a spontaneous self-crosslinking reaction after coating the Si-CSM paint and irradiating ultraviolet (UV) light through a photomask. This newly developed flexible optical Si-CSM paint can be applied in next-generation optical coatings.

Development of Diketopyrrolopyrrole-Based Smart Inks by Substituting Ionic Pendants and Engineering Molecular Packing Structures.

A series of diketopyrrolopyrrole (DPP) luminogen amphiphiles were newly designed and synthesized by a single-step anionic exchange reaction for controlling the photoluminescence properties in both solution and solid states. Multicolor emission in response to thermal, mechanical, and chemical stimuli was successfully demonstrated by engineering well-defined supramolecular assemblies. Phase transformation from the metastable amorphous solid to the stable orthorhombic crystal of [DP-Im][Br] provided the reversibly patternable light emission. Self-organization into the smectic crystalline phase of [DP-Im][TFSI] allowed us to show the linearly polarized light emission. By simultaneously applying [DP-Im][Br] and [DP-Im][TFSI], we demonstrated the fabrication of smart sensors for packaging of food or vaccines that can detect thermal attacks.

Transfer and Amplification of Iodine-Based Diacetylene Amphiphiles to Anisotropic Optical Properties by Uniaxial Orientation in Thin Films.

For flexible displays, there is a desperate need for a broadband coatable polarizer that can absorb light in a specific direction. Conventional polarizers fabricated by the polymer stretching process are too thick (50-200 µm) to be used as polarizers that can be applied to antireflective films in flexible displays. For the development of the broadband coatable thin film polarizer, diacetylene (DA) amphiphiles containing I- or I3- are newly designed and synthesized, and the content of DA amphiphiles in the 4,6-decadiyne solvent is optimized to form a lyotropic liquid crystal (LLC) phase. Topochemical polymerization of uniaxially oriented iodine-based DA not only stabilizes the film but also broadens the polarization light region from 350 to 700 nm. The transfer and amplification of iodine and DA functions in uniaxially oriented thin films enable the fabrication of broadband coatable thin film polarizers.

Imidazolium-Functionalized Diacetylene Amphiphiles: Strike a Lighter and Wear Polaroid Glasses to Decipher the Secret Code.

The development of smart inks that change color and transparency in response to external stimuli is very important for various fields, from modern art to safety and anticounterfeiting technology. A uniaxially oriented diacetylene thin film on a macroscopic area is obtained by coating, self-assembling and topochemical photopolymerizing of imidazolium-functionalized diacetylenes (M-DA and T-DA) and 4,6-decadiyne ink (70 wt%:20 wt%:10 wt%) exhibiting a lyotropic smectic A liquid-crystalline phase at room temperature. The color and transparency of letters and symbols written with the DA-based secret inks change reversibly from blue to red as well as from colorless transparent to black opaque depending on the temperature and polarization axis. A secret code written with thermoresponsive and polarization-dependent secret inks consisting of imidazolium-functionalized diacetylenes is successfully deciphered by wearing polaroid glasses and holding a burning torch.

Diacetylene-Functionalized Dendrons: Self-Assembled and Photopolymerized Three-Dimensional Networks for Advanced Self-Healing and Wringing Soft Materials.

The physical properties of supramolecular soft materials strongly depend on the molecular packing structures constructed by thermodynamically and kinetically controlled molecular self-assembly. To investigate the relationship between molecular function and self-assembled molecular packing structure, a series of diacetylene (DA)-based supramolecules was synthesized by chemically connecting flexible dendrons to DA with amide (aDA-D) or ester (eDA-D) functions. The three-dimensional (3D) organogel network of amide-functionalized aDA-D was prepared in both polar and nonpolar solvents due to the intermolecular hydrogen bonding. 3D networks of aDA-D can be further stabilized by topochemical photopolymerization. The self-healing behavior of aDA-D was observed in the sheet-like structure formed in n-dodecane by the hydrophobic interaction between the gelator and solvent. The wringing behavior of aDA-D was also demonstrated using the dynamic interaction of amide function with n-butanol solvent. Kinetically controlled and photostabilized 3D networks can be a key component from biomedical devices to soft robotic applications.

Programmed Hierarchical Hybrid Nanostructures from Fullerene-Dendrons and Pyrene-Dendrons.

The construction of fullerene (C60 ) hierarchical nanostructures with the help of amphiphilic molecules remains a challenging task in nanoscience and nanotechnology. Utilizing the host-guest complex concept, sub-10 nm layered superstructures are constructed from a monofunctionalized C60 dendron (C60 D, guest) and tweezer-like pyrene dendron (PD, host). Since C60 D and PD are asymmetric shape amphiphiles having liquid crystal (LC) dendrons, both C60 D and PD construct head-to-head bilayer superstructures by themselves. From fluorescence titration experiments, it is realized that the host-guest complex shows 1:1 stoichiometric binding with a binding constant (Ksv = 2.45 × 105 m-1 ). Based on the morphological observations and scattering analyses, it is found that buckle-like asymmetric building blocks (C60 D·PD) are self-assembled by the host-guest complex and construct multilayer hybrid nanostructures. The hierarchical hybrid nanostructures consist of the self-assembled C60 D·PD bilayer with a 2D C60 ·P nanoarray sandwiched between LC dendrons. This advanced strategy is expected to be a practicable and rational guideline for the fabrication of programmed hierarchical hybrid nanostructures.

Anisotropic Thermal Interface Materials: Directional Heat Transfer in Uniaxially Oriented Liquid Crystal Networks.

For the development of anisotropic thermal interface materials (TIMs), a rod-shaped reactive monomer PNP-6MA is newly designed and successfully synthesized. PNP-6MA reveals a smectic A (SmA) mesophase between crystalline (K) and isotropic (I) phases. PNP-6MA can be oriented under a magnetic field ( B = 2 T), and its macroscopic orientation can be robustly stabilized by in situ polymerization. Even without macroscopic orientations, the fabricated thermal conducting liquid crystal (TCLC) films show the outstanding thermal conductivity of 1.21 W/m K, which is higher than conventional organic materials. The thermal conductivity of uniaxially and macroscopically oriented TCLC films can be 2.5 W/m K along the long axis of mesogenic core. The newly developed TCLC film can be used as a TIM between a high-power light-emitting diode and a heat sink.