Externally induced color‐ and shape‐changes in micrometer‐sized objects are of great interest in novel application fields such as optofluidics and microrobotics. In this work, light and temperature responsive micrometer‐sized structural color actuators based on cholesteric liquid‐crystalline (CLC) polymer particles are presented. The particles are synthesized by suspension polymerization using a reactive CLC monomer mixture having a light responsive azobenzene dye. The particles exhibit anisotropic spot‐like and arc‐like reflective colored domains ranging from red to blue. Electron microscopy reveals a multidirectional asymmetric arrangement of the cholesteric layers in the particles and numerical simulations elucidate the anisotropic optical properties. Upon light exposure, the particles show reversible asymmetric shape deformations combined with structural color changes. When the temperature is increased above the liquid crystal‐isotropic phase transition temperature of the particles, the deformation is followed by a reduction or disappearance of the reflection. Such dual light and temperature responsive structural color actuators are interesting for a variety of micrometer‐sized devices.

Titanium dioxide (TiO2) is a key component of diverse optical and electronic applications that exploit its exceptional material properties. In particular, the use of TiO2 in its single-crystalline phase can offer substantial advantages over its amorphous and polycrystalline phases for existing and yet-to-be-developed applications. However, the implementation of single-crystal TiO2 has been hampered by challenges in its fabrication and subsequent surface functionalization. Here, we introduce a novel top-down approach that allows for batch fabrication of uniform high-aspect-ratio single-crystal TiO2 nanostructures with targeted sidewall profiles. We complement our fabrication approach with a functionalization strategy that achieves dense, uniform, and area-selective coating with a variety of biomolecules. This allows us to fabricate single-crystal rutile TiO2 nanocylinders tethered with individual DNA molecules for use as force- and torque-transducers in an optical torque wrench. These developments provide the means for increased exploitation of the superior material properties of single-crystal TiO2 at the nanoscale.

Deflecting light with high efficiency over large angles with thin optical elements is challenging but offers tremendous potential for applications, such as wearable displays and optical communication systems. Compared to the complex production of metasurfaces, the self-organization of liquid crystal (LC) superstructures provides an elegant and flexible way to produce high-quality thin optical components. The periodically varying dielectric tensor in short-pitch chiral LC gives rise to a photonic bandgap, which can be exploited to realize efficient diffractive mirrors in the visible wavelength range. However, large-angle diffractive devices require a small in-plane period, leading to complex self-assembly behavior in the bulk. This work demonstrates that by patterning photo-alignment layers at the surfaces with a period comparable to the chiral pitch, the LC self-assembles into a tilted, defect-free helical structure. The director configuration is calculated by finite element simulations and it is experimentally demonstrated that a single photo-aligned substrate is sufficient to template the tilted chiral structure in the bulk. This structure effectively (88%) diffracts light over large angles (~46°) and enables novel micrometer-thin (~3 µm) optical components that can be produced with an elegant manufacturing process. Due to flexibility of photo-alignment, this process could easily be implemented in emerging photonic applications. Miniaturized optical components such as diffraction gratings and lenses have become essential in many applications, ranging from optical communication systems to electronic

Photon absorption and emission play a key role in our understanding of how light interacts with matter. An attractive system to explore these processes are semiconductor nanoparticles (SNP) with their distinguishable photoluminescence, which makes them widely applied in optoelectronics, laser technology, and biophotonics. In current implementations of SNP, there is only partial control over anisotropy in absorption or in emission, which limits their applicability in photonics. An emerging strategy to attain a certain degree of anisotropy is to embed a quantum dot in semiconductor shell structure. Here, we report how designing the shell geometry and the position of the quantum dot enables extended control over the anisotropy in absorption and emission by a core/shell nanoparticle in a solvent. Based on the dielectric effect, our approach provides an accessible route to achieve sharply contrasting anisotropies that may even have an opposite sign. Using this unique feature, we propose cross particles to transform unpolarized blue light into polarized red and green light for liquid crystal backlights and thumbtack particles to absorb sunlight and efficiently emit photons in a solar concentrator. The strong anisotropic contrast between absorption and emission of SNP may advance energy-efficient technology, biodiagnostics, and quantum information, as well as offer new insights on light–matter interaction at the nanoscale.

A layer of chiral liquid crystal (CLC) with a photonic bandgap in the visible range has excellent reflective properties. Recently, two director configurations have been proposed in the literature for CLC between two substrates with periodic photo-alignment: one with the director parallel to the substrates and one with the director in the bulk parallel to the tilted plane. The transmission experiments under large angles of incidence (AOI) presented in this work prove that, in the bulk, the director does not remain parallel with the substrates. Because of the inclined helical axis, the full reflection band can be observed at a smaller AOI than in planar CLC. For sufficiently large AOI, the reflection of diffracted light is prohibited by total internal reflection and efficient diffraction occurs in the forward direction.