Aggregation-Caused Quenching-Type Naphthalimide Fluorophores Grafted and Ionized in a 3D Polymeric Hydrogel Network for Highly Fluorescent and Locally Tunable Emission

Abstract

Polymer hydrogels with intense yet tunable fluorescence are of great research interest due to their wide potential use in biological imaging, sensing, information storage, etc. However, the conventional fluorophores such as naphthalimide and its derivatives are usually not recommended to prepare highly fluorescent hydrogels because of their aggregation-caused quenching (ACQ) nature and spontaneous tendency to undergo fluorescence self-quenching in quasi-solid-state hydrogel systems. Additionally, local regulation over fluorescent behavior of hydrogels, despite being important, still remains underdeveloped. Herein, we report highly fluorescent polymeric hydrogels based on conventional ACQ-type naphthalimide fluorophores, followed by spatial and temporal control of their fluorescent behavior. The hydrogels were prepared by one-pot radical copolymerization of naphthalimide-containing monomer and acrylamide in chitosan−acetic acid solution. Their intense emission comes from synergetic anchoring and diluting effect of the protonated naphthalimide moieties grafted on polymer chains, which result in the electrostatic repulsion among ACQ luminogens and reduced PET (photoinduced electron transfer) effect from adjacent dimethylamine groups to naphthalimide fluorophores. After being deprotonated in alkaline conditions, both PET and the ACQ effect work again to greatly quench fluorescence, endowing the hydrogels with pH-sensitive emission behavior. These properties encourage us to develop a diffusion-reaction (D-R) method to spatially and temporally control their fluorescent behavior. Based on these results, the ion-transfer-printing-assisted D-R method was further developed to fabricate many high-precision and meaningful fluorescent patterns on hydrogels. These fluorescent patterns are invisible under daylight but become vivid under specific UV light illumination, suggesting their wide potential applications in information security and transmission.

Dual‐Encryption in a Shape‐Memory Hydrogel with Tunable Fluorescence and Reconfigurable Architecture

“…For example, enhanced encryption of information has been realized in a hydrogel by locally quenching the fluorescence and tuning the crosslinking density through chemical treatments for fluorescence imaging and shape morphing, respectively. [ 11c ] However, the resultant fluorescent pattern was not stable and had relatively low resolution due to the diffusion of chemicals and weak interaction with the fluorescent motifs; [ 12 ] information cannot be repeatedly encrypted in the gel because of the network destruction in conditions for the recovery of shape or fluorescence. [ 11c ] There is a great interest to develop tough SMPs with stable and rewritable fluorescent patterns for reprogrammable information display and encryption.…”

Recent progress in the shape deformation of polymeric hydrogels from memory to actuation

“… 99 Shape deformation hydrogels that can generate movement in response to certain external stimuli have been regarded as an emerging information storage material. 100 Recently, shape deformation hydrogels with incorporated fluorescent behavior 101,102 that provide multi-dimensional information encryption have been developed. For example, we demonstrated a fluorescent-hydrogel-based 3D anti-counterfeiting platform, which was fabricated by mixing a fluorescent macromolecule, perylene-tetracarboxylic-acid-modified gelatin (PTG), into poly(vinyl alcohol) (PVA) hydrogels ( Fig.…”

Naphthalimide‐Based Fluorescent Polymers for Molecular Detection

“…[ 10,11 ] During the recent years much attention has been paid to the design and preparation of different architectures based on 1,8‐naphthalimide. [ 12–17 ] A number of strategies have been developed to synthesize fluorescent functional materials involving naphthalimide derivatives. [ 13–18 ]…”

“…[ 12–17 ] A number of strategies have been developed to synthesize fluorescent functional materials involving naphthalimide derivatives. [ 13–18 ]…”