Broad‐Wavelength Light‐Driven High‐Speed Hybrid Crystal Actuators Actuated Inside Tissue‐Like Phantoms

Abstract

Research on molecular crystals exhibiting light‐driven actuation has made remarkable progress through the development of various molecules and the identification of driving mechanisms. However, crystals developed to date have been driven mainly by ultraviolet (UV) or blue light irradiation, and driving by red or near‐infrared (NIR) light has not been attempted yet. Herein, a broad‐wavelength light‐driven molecular crystals that exhibit high‐speed bending by photothermal effect is developed. Titanium carbide (Ti3C2Tx) MXene nanosheets are integrated into salicylideneaniline crystals to extend the wavelength range that causes photothermally driven bending to UV, visible, and NIR light. In addition, unlike the thin pristine molecular crystals that show slow photoisomerization‐induced bending only under UV light, the MXene layer enables the molecular crystals to be actuated rapidly regardless of their thickness over a wide range of wavelengths. The hybridization of molecular crystals with MXene, which exhibits strong biocompatibility as well as NIR light‐driven photothermal effect, allows for the bending of the hybrid crystals inside agar phantoms mimicking biological tissue. Last, it is confirmed that MXene hybridization can be extended to common molecular crystals including various salicylideneaniline and anisole derivatives.

Hybrid and composite materials of organic crystals

“…Sitti et al developed a novel type of hybrid crystal actuator that demonstrates rapid bending under broad-wavelength light, including UV, visible, and near-infrared (NIR) light. 93 These actuators were prepared by integrating nanosheets of titanium carbide (Ti 3 C 2 T x ) with salicylideneaniline crystals. The incorporation of MXene enables rapid actuation, transforming the light energy into mechanical energy.…”

Design and mechanism of photothermal soft actuators and their applications

“…130 Furthermore, 2D and 3D structured photothermal materials have strong light absorption capability and consequently generate higher heat conversion efficiency. 131–133 Plasmonic metal nanostructures have large absorption cross-sections and can convert light into heat through localized surface plasmon resonances. 134 Nanostructured semiconductors like metal oxides and chalcogenides can improve the photothermal conversion efficiency by bandgap engineering or free-carrier-induced localized surface plasmon resonances.…”

Negative to positive axial thermal expansion switching of an organic crystal: contribution to multistep photoactuation

“…Even though the deformations by the photothermal effect are small compared to those by photoisomerisation, the photothermal effect is advantageous in that it can achieve higher-speed actuation, a wider light wavelength range, the actuation of thicker crystals, and a broad variety of target materials. 6 b ,15 For instance, hybrid organic crystals coated with MXene—popular photothermal material with absorption from the UV to visible and near infrared region—can be actuated by the photothermal effect in a wide range of wavelengths from UV to visible 18 b and near infrared, 18 which is impossible by photoisomerisation. However, the bending behaviour has been limited to monotonous bending away 14,15,17 because typical organic crystals exhibit PTE over the entire temperature range.…”