Naphthalimide‐Based Aggregation‐Induced Emissive Polymeric Hydrogels for Fluorescent Pattern Switch and Biomimetic Actuators

Abstract

Substituted naphthalimide (NI) moieties are highly versatile and newly recognized aggregation‐induced emission (AIE) building blocks for many potentially useful smart molecules, polymers, and nanoparticles. However, the introduction of NI fluorophore into cross‐linked polymeric networks to prepare AIE‐active hydrogels still remains underdeveloped. Herein, a novel naphthalimide‐based aggregation‐induced emissive polymeric hydrogel is reported, followed by its proof‐of‐concept applications as fluorescence pattern switch and biomimetic actuator. The hydrogel, bearing semi‐interpenetrating polymer networks, is synthesized starting from N‐isopropylacrylamide, hydroxyethyl methacrylate, and a newly designed NI monomer (4‐phenoxy‐N‐allyl‐1,8‐naphthalimide, PhAN). Rational molecular design for AIE‐active PhAN monomer lies in modification of the NI core with rigid and bulky phenoxy group to break its planarity to produce desirable propeller‐shaped molecular conformation. The as‐prepared hydrogel is proved to be a aggregation‐induced blue‐light‐emitting hydrogel. It also shows volume phase transition behavior and is endowed with thermally responsive synergistic emission and transmittance change, thus enabling simultaneous regulation of two optical properties merely by one single stimulus. These useful advantages further encourage fabrication of several proto‐type fluorescence pattern switching and biomimetic actuating devices. This study may not only enlarge the list of fluorescent hydrogels but also serve as a novel smart optical platform for potential anticounterfeiting, sensing, displaying, or actuating applications.

Recent advances in colour-tunable soft actuators

“…79 For example, an anisotropic bilayer actuator was produced by utilizing an AIE-active (4-phenoxy-N-allyl-1,8-naphthalimide) PhAN/PNIPAM hydrogel film as an actuating layer and a film of pan paper as a passive layer. 80 The actuator realized thermo-induced simultaneous shape-morphing behaviour and optical changes (enhancements in fluorescence intensity). Its actuation behaviour was caused by the mismatch in the thermo-regulated swelling ratios and the modules between the bilayers.…”

Intelligent Polymer‐Based Bioinspired Actuators: From Monofunction to Multifunction

“…Comparatively, stimuli–responsive hydrogels, usually in forms of 3D networks of hydrophilic polymers filled with aqueous solutions and enabling macroscopic volume changes through swelling or shrinking in response to various external stimuli, are particularly promising in biomedical fields. [ 22 ] They are usually formed by the polymerizations of monomers or the crosslinking of polymers using materials such as N ‐isopropylacrylamide, [ 23 ] sodium alginate, [ 24 ] gelatin, [ 25 ] acrylamide, acrylic acid, [ 26 ] and so on. Due to their similarities to the native extracellular matrix (ECM) which provide mechanical support and 3D microenvironments for cell attachment and ingrowth and transport channels for nutrients and metabolites, the bioinspired actuators based on the stimuli–responsive hydrogels hold special promise in various biomedical areas such as drug delivery and tissue engineering.…”

Multi-level encryption of information in morphing hydrogels with patterned fluorescence

“…So far, many strategies have been employed for data encryption, such as holographic imaging, 1,2 photonic crystals, 3,4 watermarks, 5,6 and patterned fluorescence/phosphorescence. 7–13 Among these methods, fluorescence imaging has aroused tremendous attention as it becomes readable only under ultraviolet light irradiation with an appropriate wavelength, rather than in daylight. 14,15 Owing to their close similarity to soft biotissues and promising applications in aqueous and biological environments, 16–19 hydrogels are recognized as ideal materials to carry fluorescent information.…”