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Thermoplasmonics deals with the generation and manipulation of nanoscale heating associated with noble metallic nanoparticles. To this end, gold nanoparticles (AuNPs) are unique nanomaterials with the intrinsic capability to generate a nanoscale confined light‐triggered thermal effect. This phenomenon is produced under the excitation of a suitable light of a wavelength that matches the localized surface plasmonic resonance frequency of AuNPs. Liquid crystals (LCs) and hydrogels are temperature‐sensitive materials that can detect the host AuNPs and their photo‐induced temperature variations. In this perspective, new insight into thermoplasmonics, by describing a series of methodologies for monitoring, detecting, and exploiting the photothermal properties of AuNPs, is offered. From conventional infrared thermography to highly sophisticated temperature‐sensitive materials such as LCs and hydrogels, a new scenario in thermoplasmonic‐based, next generation, photonic components is presented and discussed. Moreover, a new road in thermoplasmonic‐driven biomedical applications, by describing compelling and innovative health technologies such as on‐demand drug‐release and smart face masks with smart nano‐assisted destruction of pathogens, is proposed. The latter represents a new weapon in the fight against COVID‐19.

Light is a readily available and sustainable energy source. Transduction of light into mechanical work or electricity in functional materials, composites, or systems has other potential advantages derived from the ability to remotely, spatially, and temporally control triggering by light. Toward this end, this work examines photoinduced piezoelectric (photopiezoelectric) effects in laminate composites prepared from photoresponsive polymeric materials and the piezoelectric polymer polyvinylidene fluoride (PVDF). In the geometry studied here, photopiezoelectric conversion is shown to strongly depend on the photomechanical properties inherent to the azobenzene-functionalized polyimides. Based on prior examinations of photomechanical effects in azobenzene-functionalized polyimides, this investigation focuses on amorphous materials and systematically varies the concentration of azobenzene in the copolymers. The baseline photomechanical response of the set of polyimides is characterized in cantilever deflection experiments. To improve the photomechanical response of the materials and enhance the electrical conversion, the polyimides are drawn to increase the magnitude of the deflection as well as photogenerated stress. In laminate composites, the photomechanical response of the materials in sequenced light exposure is shown to transduce light energy into electrical energy. The frequency of the photopiezoelectric response of the composite can match the frequency of the sequenced light exposing the films.

Soft composite materials combined with a holographic photopolymerization process are used for realizing an innovative switchable periodic structure made of slices of almost pure polymer alternated with films of well aligned nematic liquid crystals named POLICRYPS. It exhibits negligible scattering losses, while the effect of the spatial modulation of the refractive index (from polymer to nematic liquid crystal) can be switched on and off by applying a low (few V/μm) electric field. The diffractive properties of the POLICRYPS structure are characterized in terms of cell thickness, impinging probe angle and wavelength revealing a strong correlation between the diffraction efficiency and all the above mentioned parameters. These results are very attractive for many applications such as switchable Bragg gratings for telecom devices, phase modulators, and displays. Other advantages of the technology include absence of an alignment layer, absence of haze, robust structure, and inexpensive manufacturing. In addition, no special alignment layers are required. This is a unique opportunity and a big advantage compared to conventional liquid crystal devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 158–162

Circularly polarized light is employed to write information into cholesteric liquid crystal (CLC) cells that initially exhibit homogeneous planar alignment and are fabricated with a photoaligning boundary layer. Overlap of the writing beam with light reflected from the CLC phase disrupts the reflective Grandjean texture, resulting in a localized region that strongly scatters light. These scattering areas can be geometrically patterned using circularly polarized light and a mask, erased and brought back to the original reflective condition by exposure to linearly polarized light, and then repatterned with a different mask using circularly polarized light. The light-induced scattering is localized to the side of the cell being exposed. Within the scattering region a microscopic texture is formed, which exhibits an average feature, or “domain”, size related to cell thickness and helical pitch. The behavior occurs only when the CLC and incoming writing radiation exhibit the same handedness and when the reflection bandwidth of the CLC is commensurate with the wavelength of the incoming radiation. This new phenomena provides the ability to reconfigure reflectivity from a CLC cell and is expected to be useful for systems where all optical control of dynamic information is needed.

Photosensitive liquid crystals (PLCs) are promising materials that can combine a high-refractive-index modulation, typical of LCs, with high photosensitivity, due to the presence of photochromic molecules such as azobenzene and derivates. [1] These can undergo a reversible isomerization from a thermodynamically stable trans to a cis conformation when acted on by UV or visible light; a reverse transition can be obtained upon heating or irradiation with a different (longer wavelength) visible light. Thanks to these materials andprocesses, thepossibility toconfine and stabilize photosensitive materials has been considered in the past [2] and the perspective of producing fast photonic devices of scientific and technological interest looks highly realistic. There is, however, a serious problem represented by instability far from room temperature. [2] One way to reduce this effect has been found in using composite polymeric materials: [3] Holographic diffraction gratings, which exploit LC composite materials (HPDLCs), [4] are low-cost components with a wide range of possible photonic and optoelectronics applications. Therefore, the possibility of fabricating an optically controllable photonic device has been investigated by combining the photosensitivity of azobenzene materials with the optical properties of HPDLCs. [5] Devices of this kind can exhibit, however, an intrinsic drawback when the droplet size of the LC component inside the polymeric matrix is comparable with the wavelength of the diffracted light, thus yielding a strong light scattering. [6] Recently, a good improvement has been obtained by using a new kind of holographic diffraction grating with better optical qualities, which consists of polymer slices alternated to films of regularly aligned nematic LC (NLC). Depending on the particular procedure utilized for its fabrication, this structure is called POLIPHEM [7] orPOLICRYPS [8] andisobtainedby UV-curingofa mixture of monomer and NLC. In a recent attempt [9] to fabricate

Phototuning of more than 2000 nm is demonstrated in an azobenzene-based cholesteric liquid crystal (azo-CLC) consisting of a high-helical-twisting-power, axially chiral bis(azo) molecule (QL76). Phototuning range and rate are compared as a function of chiral dopant concentration, light intensity, and thickness. CLCs composed of QL76 maintain the CLC phase regardless of intensity or duration of exposure. The time necessary for the complete restoration of the original spectral properties (position, bandwidth, baseline transmission, and reflectivity) of QL76-based CLC is dramatically reduced from days to a few minutes by polymer stabilization of the CLC helix.

Mixtures of cholesteric liquid crystals doped with high clearing temperature azobenzene nematic liquid crystals are shown to possess large, fast, and reversible dynamic photosensitive features. Selective wavelength shifts approaching 400 nm are reported, and depending on the host cholesteric liquid crystal, both red-shifted and blue-shifted wavelength changes can be induced. The photoinduced states of these material systems are shown to be stable for long periods of time upon removal of the radiation source, completely reversible, and dynamically fast. These phototunable features are demonstrated using both continuous wave (CW) and nanosecond laser beams. The latter is used to change the selective reflection wavelength from blue to green with a single nanosecond pulse and the ability to write information into these films using these processes are demonstrated.