Supramolecular Hyperbranched Poly(amino ester)s with Homogeneous Electron Delocalization for Multi‐Stimuli‐Responsive Fluorescence

Abstract

Nonconventional luminogens without conjugated chromophores have attracted much interest for their intriguing fluorescence and potential wide applications. Their emission mechanism, however, remains an open question. Herein, hyperbranched poly(amino ester) (HPAE) with novel structure is synthesized through a simple one‐pot polycondensation reaction. The HPAE exhibits strong fluorescence and aggregation‐induced emission (AIE) characteristic. Transmission electron microscopy and theoretical calculation results demonstrate that the fluorescence is attributed from electron delocalization in the supramolecular self‐assemblies of HPAE. Meanwhile, supramolecular self‐assemblies, induced by the synergy effect of inter/intramolecular hydrogen bond and amphipathicity of HPAE, rigidify the molecule conformation, leading to enhanced fluorescence. Furthermore, the HPAE exhibits single‐color emission due to its generation of homogeneous electron delocalization. Interestingly, such HPAE shows multi‐stimuli‐responsive fluorescence to solvent, temperature, pH, and Fe3+. Therefore, this work not only provides an important step forward in exploring the emission mechanism of nonconventional luminogens, but also develops a multi‐functional unconjugated AIE probe.

Nontraditional Organic/Polymeric Luminogens with Red‐Shifted Fluorescence Emissions

“…Based on the type of heteroatoms other than carbon and hydrogen atoms in the nonconventional chromophores, the NTLs can be roughly classified into following categories (Figure 1) 1) Oxygen-containing NTLs: alcohols (d-fructose, d-(+)-xylose, d-galactose, and pentaerythritol), [30] ethers [poly(ethylene glycol) (PEG), [31] and hyperbranched polyether epoxy (EHBPE)], [23] carboxylic acids [poly(acrylic acid) (PAAc)], [32] anhydrides [poly(itaconic anhydride) (PITA), [33] and poly(maleic anhydride)], [16,34] and esters [polycarbonate, [35] and poly(lactic acid) binary blends]. [36] 2) Nitrogen-containing NTLs: amines [poly(amido amine) (PAMAM), [37,38] hyperbranched poly(amino ester) (PAE), [39,40] and poly(amino ether ester)], [41] imines [linear or hyperbranched polyethyleneimine (PEI)], [42][43][44] oximes (hexanal oximes), [11] nitriles [polyacrylonitrile (PAN)], [17] amides [polyacrylamide (PAAm), [45] poly(N-isopropylacrylamide) (PNIPAM), [32] poly(ether amide) (PEA), [46] poly(esteramide-ether) (PEAE), [47] and poly(amido acids)], [48] imides (polysuccinimide), [20,22] polyurethane, [49,50] amino acids, [51,52] and lactams [polyvinylpyrrolidone (PVP), [53] and poly(Nvinylcaprolactam) (PNVCL)]. [54] 3) Sulfur-containing NTLs: thiols (cysteine), sulfones (polysulfone), [55] sulfonic acids [perfluorosulfonate ionomers (PFSI)], [10] sulfonates [poly(4-vinylpyridine)butane-1sulfonate (PVP-S)], [56] and thiourea.…”

Fluorescence Behavior and Mechanisms of Poly(ethylene glycol) and Their Applications in Fe3+ and Cr6+ Detections, Data Encryption, and Cell Imaging

“…This phenomenon is termed cluster-triggered emission (CTE). − In comparison to the traditional organic fluorescent paradigm, these materials are easy to process, and there is practically unlimited possibilities of functionalization through their preparations and postmodifications, providing a large potential to adjust their emission behaviors with regard to specific applications. To date, a vast variety of studies have been conducted, concerning different heteroatom-containing polymer chains, including, for instance, poly­(amidoamine), poly­(aminoester), , polysiloxane, , polyethylenimine, − polyurethane, polyurea, , polyether, and copolymers of maleic anhydride-vinyl acetate and its alkali metal salts. , Smart luminescent materials with tunable multicolor emission have also been reported recently, based on unconventional luminophores, containing only oxygen atoms and free of π-bonding, which also exhibit typical CTE behavior, a pioneer study on small organic molecules rather than polymers. Quite comprehensive reviews updating this subject have been done recently , in which different terms are used for these materials, such as clusteroluminogens, nonconventional luminophores, as well as nontraditional intrinsic luminogens (NTIP), in contrast to the traditional luminescence paradigm (TLP) …”

Oleic Acid Constructed Supramolecular Hyperbranched Polysiloxane with Enhanced Fluorescence and Excellent Drug Delivery Ability

“…Thus, as shown in Figure S14 in the Supporting Information, in acetone-ethanol solution the HBPSi part in HBPSi-OA2 will distribute in the core of self-assembly, while the oleic acid distributes in the shell, as a result, most free functional groups are forced to aggregate and form larger electron delocalizations. [25,26] That is why excitation at 260 and 300 nm disappears. On the contrary, water is a good solvent for HBPSi, however, a poor solvent for oleic acid.…”