Dynamic Photochromic Polymer Nanoparticles Based on Matrix-Dependent Förster Resonance Energy Transfer and Aggregation-Induced Emission Properties

Abstract

Dynamic color-tunable fluorescent materials are soughtafter materials in many applications. Here, we report a polymeric matrix-regulated fluorescence strategy via synergistically modulating aggregation-induced emission (AIE) properties and the Forster resonance energy transfer (FRET) process, which leads to tunable dynamic variation of color and photoluminescence (PL) intensity of fluorescent polymeric nanoparticles (FRET-PNPs) driven by photoirradiation. The FRET-PNPs were prepared via a facile one-pot miniemulsion copolymerization with the tetraphenyletheyl (TPE) and spiropyran (SP) units chemically bonded to the polymer matrix. The FRET-PNPs exhibited dynamic variation of fluorescence properties (colors and PL intensity) under photoirradiation on the timescale of minutes. The variation of the polymer matrix composition could deliberately influence the AIE property of TPE units and the isomerization process of SP to merocyanine units, which further affect the FRET efficiency of FRET-PNPs and, eventually, lead to versatile dynamic fluorescence variation. The dynamic fluorescence property as well as the excellent processability and film formation ability of FRET-PNPs allowed for diverse applications, such as warning labels, dynamic decorative painting, and multiple information encryption. Without sophisticated molecular design or tedious preparation processes, a new perspective for the design, fabrication, and performance optimization of fluorescent nanomaterials for innovative applications was proposed.

Delicate and Independent Manipulation of Dynamic Fluorescence Behavior of Polymer Nanoparticles Based on a Core–Shell Strategy

“…All of the fluorescent compounds were synthesized via the protocols reported in our previous work. , For the synthesis of TPE-PBE, TPE-B was first coupled with the Suzuki–Miyaura reaction to gain the phenolic derivative TPE-P, and then the hydroxyl group was substituted by 4-bromo-1-butene to give TPE-PBE (Scheme S1). In addition, (R/S)-2-(3′,3′-dimethyl-6-nitro-3′H-spiro-[chromene-2,2′-indol]-1′-yl) ethanol (SPOH) was synthesized with 5-nitrosalicylaldehyde and a bromide salt that was obtained by a quaternary ammonium of 2,3,3-trimethyl-3 H -indole and 2-bromoethanol, and then SPOH was modified with acryloyl chloride to obtain SPEA (Scheme S2).…”

“…As shown in the previous section, the dynamic fluorescence behavior of CS-FPNPs is a complicated result of TPE emission, reversible photoisomerization of SP and MC units, MC emission, and FRET process of TPE and MC units. It has been reported that the TPE emission and reversible photoisomerization of SP and MC units highly depend on the polymer matrix structure . For example, the rigid polymer matrices promote the TPE emission, but retard the ring-opening reaction of SP to MC units.…”

“…It has been reported that the TPE emission and reversible photoisomerization of SP and MC units highly depend on the polymer matrix structure. 29 For example, the rigid polymer matrices promote the TPE emission, but retard the ring-opening reaction of SP to MC units. On the contrary, the soft polymer matrices facilitate the photoisomerization of SP to MC units, but weaken the TPE emission.…”

“…27,28 In our previous work, polymer NPs (PNPs) with dynamic fluorescence properties based on Forster resonance energy transfer (FRET) and AIE processes were prepared through integrating an AIE donor with a photoisomerizing fluorophore in miniemulsions. 29 For dynamic fluorescence systems based on double or multiple chromophores, the most significant challenge is how to achieve finer control over the luminescence behavior of photochromic NPs, which often depends on the combination of several factors, namely, the restriction extent of AIEgens, photochemical process of photochromism compounds, and FRET process. In some cases, some trade-offs among these factors make it challenging to optimize the emission ability of photochromic NPs.…”

“…In recent years, photochromic NPs with AIE properties to achieve dynamic fluorescence behavior have been widely developed under light stimuli. − Xu et al reported two new SP molecules with the tetraphenylethylene (TPE) moiety that exhibited AIE properties as well as photochromic and acidochromic properties. Later, Liu et al developed a novel multistimuli-responsive fluorescent switch via a covalent linkage between the SP photoacid and TPE molecule. , In our previous work, polymer NPs (PNPs) with dynamic fluorescence properties based on Förster resonance energy transfer (FRET) and AIE processes were prepared through integrating an AIE donor with a photoisomerizing fluorophore in miniemulsions . For dynamic fluorescence systems based on double or multiple chromophores, the most significant challenge is how to achieve finer control over the luminescence behavior of photochromic NPs, which often depends on the combination of several factors, namely, the restriction extent of AIEgens, photochemical process of photochromism compounds, and FRET process.…”