Tetraphenylethene Cross-Linked Thermosensitive Microgels via Acylhydrazone Bonds: Aggregation-Induced Emission in Nanoconfined Environments and the Cononsolvency Effect

Abstract

We studied the aggregation-induced emission (AIE) phenomenon in a nanoconfined environment, where the AIE-active molecule, namely, 1,1,2,2-tetrakis(4-methanoylphenyl)ethane (TPE-4ALD), was held in space via four acylhydrazone bonds within the thermosensitive microgel networks. The thermosensitive microgels, namely N-AH-TPE, were synthesized via the copolymerization of N-isopropylacrylamide (NIPAM) and 4-acylhydrazine-(2-hydroxy-3-(methacryloxypropyl)pyridine hydrochloride (AH monomer) with TPE-4ALD as cross-linker via surfactant free emulsion polymerization (SFEP) in aqueous solution at 70 °C. Acylhydrazone-bonded tetraphenylethene (TPE-4AH) moieties were thus constructed and worked as the fluorophore in N-AH-TPE microgels. The aqueous suspensions of N-AH-TPE microgels exhibit strongly bluish-green fluorescence under ultraviolet excitation because the four arms of TPE-4AH moieties were held and their intramolecular motions are strongly restricted. It is estimated that there is one TPE-4AH moiety per about 394 nm 3 for the swollen N-AH-TPE microgels. The fluorescent properties of N-AH-TPE microgels can be modulated via the change of hydrophilic and hydrophobic environments of TPE-4AH moieties exerted by external stimuli, like addition of various good solvents for TPE-based structures, i.e., N,N-dimethylformamide (DMF), methanol, ethanol, tetrahydrofuran (THF), and N,Ndimethyl sulfoxide (DMSO), varying the solution temperature as well as the counteranions of the microgels. An unusual enhancement in the fluorescent intensity is observed when specific amounts of organic solvent are added into the aqueous suspensions of N-AH-TPE microgels, which can be attributed to the cononsolvency of the polyNIPAM network chains. The shrinkage of N-AH-TPE microgels caused by the cononsolvency effect further strengthens the confinement of TPE-4AH moieties and hence enhances the fluorescent emission of the microgels even though the organic solvents added are good solvents for TPE-4AH. Increasing the solution temperature of N-AH-TPE microgels or introducing hydrophobic counteranions into the microgels also significantly enhances the fluorescent emission of the microgels.

A Novel Amphiphilic AIE Molecule and Its Application in Thermosensitive Liposome

“…As a result, a great number of organic/polymeric materials containing AIE molecules have been prepared and applied in various fields, such as bioimaging, biosensing, light‐emitting devices, and the drug controlled release materials . However, reports of AIE molecules in thermosensitive nanomaterials are rare . With the aim to develop a novel thermosensitive nanomaterial, this study reported the successful fabrication of temperature‐sensitive liposomes assembled from the component lipids of conventional low‐temperature‐sensitive liposomes (LTSLs) including 1,2‐dipalmitoyl‐ sn ‐glycero −3‐phosphocholine (DPPC), 1,2‐distearoyl‐ sn ‐glycero‐3‐phosphoethanolamine‐N‐[methoxy(polye ‐thylene‐glycol)‐2000] (DSPE‐PEG‐2000) and the newly‐synthesized amphiphilic AIE molecule 4‐oxo‐4‐((1‐(stearoyloxy)‐3‐(2‐(4‐(1,2,2‐triphenylvinyl)phenoxy)acetoxy)‐propan‐2‐yl)oxy)butanoic acid (TPE‐STE).…”

Aggregation-induced emission: right there shining

“…Dynamic light scattering, neutron scattering, isotope labeling, and molecular dynamic simulation techniques have been used in the relevant investigation, but the landscape for cononsolvency effect is elusive. Through the aid of an AIEactive fluorescent probe, a clear picture was drawn by a collaborative study and careful analysis of the emission behaviors of the TPE-crosslinked thermo-sensitive microgels in a nano-confined environment [13].…”

“…(b) FL spectra of N-AH-TPE microgels in water (H 2 O)/N,Ndimethylformamide (DMF) mixtures with various water molar fractions (χ water ). (c) Plots of emission intensity at maximum emission wavelength of microgels in H 2 O/ethanol (1), H 2 O/methanol (2), H 2 O/DMF (3), H 2 O/DMSO (4), and H 2 O/THF (5) mixtures as a function of water molar fraction.Reproduced with permission from Ref [13]…”

Preparation of thermoresponsive poly(N‐vinylcaprolactam‐co‐2‐methoxyethyl acrylate) nanogels via inverse miniemulsion polymerization

“…In recent years, development of environmentally responsive polymeric nanogels has attracted tremendous attention because of their wide applications in many advanced fields including disease detection and treatment, drug delivery, sensing, and catalysis taking advantage of their rapid and sensitive responsiveness to minimal changes from environment . Polymeric nanogels with a thermoresponsive property may be one of the most intensively investigated subclasses of responsive nanogels, and many functional monomers are available to prepare thermoresponsive nanogels . Thermoresponsive behavior of polymeric nanogels is mainly determined by the type of thermosensitive polymers, and it can be easily adjusted the polymer composition through adopting homopolymerization or copolymerization of various functional monomers.…”