A Facile Approach towards Fluorescent Nanogels with AIE-Active Spacers

Abstract

A facile and efficient approach for design and synthesis of organic fluorescent nanogels has been developed by using a pre-synthesized polymeric precursor. This strategy is achieved by two key steps: (i) precise synthesis of core–shell star-shaped block copolymers with crosslinkable AIEgen-precursor (AIEgen: aggregation induced emission luminogen) as pending groups on the inner blocks; (ii) gelation of the inner blocks by coupling the AIEgen-precursor moieties to generate AIE-active spacers, and thus, fluorescent nanogel. By using this strategy, a series of star-shaped block copolymers with benzophenone groups pending on the inner blocks were synthesized by grafting from a hexafunctional initiator through atom transfer radical copolymerization (ATRP) of 4-benzoylphenyl methacrylate (BPMA) or 2-(4-benzoylphenoxy)ethyl methacrylate (BPOEMA) with methyl methacrylate (MMA) and tert -butyldimethylsilyl-protected 2-hydroxyethyl methacrylate (ProHEMA) followed by a sequential ATRP to grow PMMA or PProHEMA. The pendent benzophenone groups were coupled by McMurry reaction to generate tetraphenylethylene (TPE) groups which served as AIE-active spacers, affording a fluorescent nanogel. The nanogel showed strong emission not only at aggregated state but also in dilute solution due to the strongly restricted inter- and intramolecular movement of TPE moiety in the crosslinked polymeric network. The nanogel has been used as a fluorescent macromolecular additive to fabricate fluorescent film.

Precise Synthesis of Structurally Diverse Aggregation-Induced Emission-Active Polyacrylates by Cu(0)-Catalyzed SET-LRP with Macromolecular Structure-Correlated Emission

“…1 H NMR (600 MHz, CDCl 3 , δ): 7.16− 7.07 (m, 9H, ArH), 7.07−6.98 (m, 8H, ArH), 6.87 (d, J = 8.6 Hz, 2H, ArH), 4.53 (q, J = 6.9 Hz, 1H, CH(CH 3 )Br), 1.89 (d, J = 6.9 Hz, 3H, CH(CH 3 )Br). 13 Synthesis of TPE-2Br.…”

“…1 H NMR (600 MHz, CDCl 3 , δ): 7.07−7.01 (m, 8H, ArH), 6.94−6.88 (m, 8H, ArH), 4.55 (q, J = 6.9 Hz, 4H, CH(CH 3 )Br), 1.91 (d, J = 6.9 Hz, 12H, CH(CH 3 )Br). 13 were added to a 10 mL Schlenk tube. The reaction mixture was then deoxygenated by six freeze−pump−thaw cycles.…”

“…All reactions gave acceptable to high yields. The chemical structure of the purified initiators was confirmed by 1 H NMR, 13 C NMR, and ESI-MS (Experimental Section and Figures S1−S3). The characteristic 1 H NMR signals from methyl and methine protons of the 2bromopropionate moieties peaked at 1.89 and 4.53 ppm, respectively (Figure 1).…”

“…5,6 Generally, AIE-active polymers can be obtained by the polymerization of AIEgen-containing monomer 7,8 or from AIEgen-containing initiators, 9−11 postpolymerization modification with AIEgens, 12 or in situ formation of AIEgens from non-AIE-active precursors. 13 The strong structural designability of polymers enables the synthesis of AIE-active polymers with diverse chain topology (linear, star, hyperbrached, cyclic, etc) and the location of AIEgens at the main chain, side chain, center, or periphery. 14−22 For instance, Zhang et al reported a series of AIE-active core-cross-linked miktoarm star copolymers with temperature/pH dual responsiveness.…”

Hyperbranching-Enhanced-Emission Effect Discovered in Hyperbranched Poly(4-(cyanomethyl)phenyl methacrylate)

“…Up to now, the AIE-active luminogens (AIEgens) as organic solid luminescent materials have been developed for chemical sensors, bioimaging, drug delivery, photodynamic therapy, etc. In parallel to developing novel AIE-active molecules, the AIE-active polymers , were also proposed in which the aggregation played a constructive role in fluorescence efficiency and thus were considered as ideal fluorescent solid materials for microbeads, thin films, , and nanogels, , etc. In addition to those bearing conventional large-conjugated fluorescent moieties in the backbone or as pendent groups, , AIE-active fluorescent polymers carrying subchromophores were discovered and showed their advantaged merits such as high chain flexibility, large structural diversity, and facile preparation. − The subfluorophore was generally composed of electron-rich heteroatoms, such as nitrogen (N), , oxygen (O), sulfur (S), and phosphorus (P) .…”