Haiqin Deng

Aggregation-induced chirality, circularly polarized luminescence, and helical self-assembly of a leucine-containing AIE luminogen

Self-assembling of luminescent molecules into one-dimensional nanostructures is of particular interest in fabricating nanoscale electronic and photonic devices. Herein, we report the rational design and synthesis of a chiral fluorescent tetraphenylethylene derivative containing L-leucine methyl ester moiety (TPE-Leu). In solution, TPE-Leu is non-emissive and CD silent, but becomes highly emissive and CD active upon aggregation, exhibiting aggregation-induced emission (AIE) and chirality (AIC). Upon evaporation of its solution, TPE-Leu readily self-assembles into helical fluorescent micro/nanofibers, which show circularly polarized luminescence (CPL) and have the CPL dissymmetry factors in the range of 0.02–0.07. This molecular design combines the AIE effect, chirality, and self-assembling capability together, and is highly efficient in constructing novel functional micro/nanomaterials with well-defined structures and enhanced emission.

A Luminogen with Aggregation-Induced Emission Characteristics for Wash-Free Bacterial Imaging, High-Throughput Antibiotics Screening and Bacterial Susceptibility Evaluation.

A luminogen with aggregation-induced emission characteristics is reported for bacterial imaging and antibiotics screening studies. The luminogen can light up bacteria in a wash-free manner, which simplifies the imaging process and increases its accuracy in bacterial detection. It can also be applied to high-throughput screening of antibiotics and fast evaluation of bacterial susceptibility, giving reliable results in less than 5 h.

Efficient Polymerization of Azide and Active Internal Alkynes

The 1,3-dipolar cycloaddition of azides and active internal alkynes has been well studied, but is rarely utilized as a tool for polymer preparation. In this work, an efficient polymerization route is developed. Polycycloaddition of diazide (4) and bis(benzoylethynyl)-benzenes and -butane (3) at elevated temperature has produced the first examples of soluble 1,4,5-trisubstituted polytriazoles PI with satisfactory molecular weights (M(w) up to 16 400) in excellent yields (up to 98.6%). All the obtained polymers are thermally stable, losing merely 5% of their weights at temperatures higher than 367 °C. They exhibit higher refractive indices than some commercial plastics and can be crosslinked upon UV irradiation to generate a 3D photopattern with high resolution. The metal-free feature of such a methodology offers a facile tool to prepare functional materials free from the contamination of metal species.

Construction of regio- and stereoregular poly(enaminone)s by multicomponent tandem polymerizations of diynes, diaroyl chloride and primary amines

Polyhydroaminations for the synthesis of stable nitrogen-substituted conjugated polymers with well-defined structures remain a great challenge and the control of the regio- and stereochemistry of the enamine product of the hydroamination is non-trivial. Herein we report an efficient tandem polymerization of alkynes, carbonyl chlorides and primary amines to afford regio- and stereoregular conjugated poly(enaminone)s. The atom-economical one-pot sequential polycoupling–hydroamination polymerization catalyzed by Pd(PPh3)2Cl2/CuI proceeded smoothly under mild conditions, furnishing nitrogen-substituted conjugated polymers with high molecular weights (up to 46 100) and high regio-/stereoregularities (100%) in nearly quantitative yields (up to 99%). The single crystal structure of the model compound, together with the NMR spectra comparison of the model compound and polymers provided direct insight into the stereoselectivity of the polymerization, verifying the sole Z-vinylene isomer of the polymers. Through the exquisite structural design strategy of the intramolecular hydrogen bond of the resulting hydroamination product, the tautomerization between enamine and imine as well as E/Z isomerization was successfully avoided, providing products with high chemical stability and sole Z-vinylene isomers. The conjugated polymers display excellent solubility in common organic solvents, good film-forming ability, and high thermal stability. The hydrogen bond formation of the polymer helps to block the potential photo-induced electron transfer process and the polymer shows a unique aggregation-enhanced emission phenomenon: their solutions are weakly emissive, while their nanoaggregates or thin films are brightly emissive. Furthermore, thin films of the polymers enjoy high refractive indices (1.9103–1.6582) in a wide wavelength region of 400–1000 nm, which can be further modulated by UV irradiation. Meanwhile, well-resolved fluorescent photopatterns of the polymers can be fabricated through the UV irradiation of thin films via a copper photomask.

Fluorescent self-assembled nanowires of AIE fluorogens

The self-assembly of fluorescent molecules is of general interest due to the potential fabrication of nanostructured materials. The fabrication of fluorescent nanowires remains challenging because the inherent aggregation in the self-assembly process quenches the fluorescence of the molecules in many cases. In this work, new aggregation-induced emission-active tetraphenylethene derivatives were used to fabricate fluorescent nanowires facilely by self-assembly processes. Moreover, the fluorescent nanowires can further self-assemble to form macroscopic fluorescent thin films in the solution. The detailed self-assembly processes from nanospheres to nanowires, and further to fluorescent macroscopic thin films were elucidated and evidenced by SEM imaging. A phenomenon of photo-induced emission enhancement was observed, owing to the photo-induced ring-closing oxidative reaction of the tetraphenylethene core.

Regio- and stereoselective construction of stimuli-responsive macromolecules by a sequential coupling-hydroamination polymerization route

Herein we reported a new facile one-pot multicomponent sequential polymerization approach for the construction of conjugated nitrogen-substituted polymers. Catalyzed by Pd(PPh3)2Cl2/CuI at room temperature, the coupling-hydroamination polymerizations of 1,2-bis(4-ethynylphenyl)-1,2-diphenylethene, terephthaloyl chloride and secondary aliphatic amines proceeded smoothly in a regioregular and stereoselective manner, furnishing poly(arylene enaminone)s (PAEs) with high molecular weights (Mw up to 34 600) in satisfactory yields (up to 91%). A model compound was elaborately designed and synthesized to verify the chemical structures of the corresponding polymeric products. All the PAEs exhibited good solubility in common organic solvents and were thermally stable with degradation temperatures of up to 313 °C under nitrogen. They possessed good film-forming ability and their thin solid films showed high refractive indices (RI = 1.9318–1.6320) in a wide wavelength region of 400–1000 nm, whose value could be further modulated by UV irradiation. Although the model compound and the PAEs possessed a typical aggregation-induced emission luminogen of tetraphenylethene, they were weakly emissive either in solution or in the aggregated state, due to the photoinduced electron transfer (PET) effect. Their strong emission in the aggregated state could be readily recovered by the blockage of the PET effect through protonation of the amino groups. Thus, this work demonstrated a powerful polymerization tool to access conjugated polymeric materials with pH-responsive properties.

Development of a transition metal-free polymerization route to functional conjugated polydiynes from a haloalkyne-based organic reaction

The development of an efficient transition metal-free polymerization route has been an active research topic in polymer science owing to its low synthetic cost and decreased metal residue and hence elevated material performance in the products. In this work, we report a new such method for constructing conjugated polydiynes based on the organic reaction of 1-haloalkyne. In the presence of potassium iodide, the polymerizations of 1,2-bis[4-(iodoethynyl)phenyl]-1,2-diphenylethene (1), 1,4-bis(2-iodoethynyl)benzene (2) and 4,4′-bis(2-iodoethynyl)-1,1′-biphenyl (3) proceed smoothly in N,N-dimethylformamide at 120 °C under nitrogen, producing P1–3 consisting of alternate aromatic and 1,3-diyne moieties in moderate to satisfactory yields. While P1 possesses good solubility in common organic solvents, P2 and P3 are insoluble due to their rigid structures. All the polymers are thermally stable, losing 5% of their weight at a high temperature of up to 352 °C. A homogeneous film of P1 can be readily obtained by spin-coating its solution, which shows high and UV-tunable refractive index (n = 2.1125–1.7747) in a wide wavelength range (400–900 nm). A well-defined fluorescent photopattern can be generated by UV irradiation of the polymer film through a copper mask. This work thus opens a new avenue for constructing conjugated polymers with advanced functionalities.

Multicomponent polymerization: development of a one-pot synthetic route to functional polymers using diyne, N-sulfonyl azide and water/ethanol as reactants

Green chemistry shows the advantages of a simple synthetic process, low cost of production, a clean working environment and reduction of harmful wastes. In this work, we used naturally occurring materials to prepare functional polymers. The polymerizations of 1,2-bis(4-ethynylphenyl)-1,2-diphenylethene, disulfonyl azide, and water together with ethanol were catalyzed by copper(I) iodide and triethylamine in a mild, efficient and atom-economical fashion, generating soluble polymers with high molecular weights in satisfactory isolation yields. By controlling the adding amount of water and ethanol, the ratio of amide and imidate units in the polymer chain could be readily modulated. Their good solubility allows the polymers to show outstanding film-forming ability. Due to the tetraphenylethene moieties embedded in the polymer chains, the polymer solutions emit faintly, but their aggregates fluoresce intensely, demonstrating a characteristic of aggregation-induced emission. Such results are anticipated to accelerate the development of efficient and economical one-pot multicomponent polymerizations toward functional polymeric materials.

Multicomponent sequential polymerizations of alkynes, carbonyl chloride and amino ester salts toward helical and luminescent polymers

Multicomponent sequential reactions have recently received much attention owing to their outstanding advantages, such as simple operation, atom economy, and environmental benefit. In this work, we report a new multicomponent sequential reaction and the corresponding multicomponent sequential polymerization approach to construct conjugated structures with advanced functionalities. By employing 1,8-diazabicyclo[5.4.0]undec-7-ene as an additive, alkynes, carbonyl chloride and amino ester salts undergo a one-pot three-component sequential reaction successfully. Similarly, the derived multicomponent sequential polymerizations of diyne, terephthaloyl chloride and amino ester proceed smoothly in a regio- and stereoregular manner and generate conjugated nitrogen-substituted poly(enaminone)s with high molecular weights in satisfactory yields. All the resulting polymers are soluble in common solvents, and possess high thermal stability and good film-forming ability. Interestingly, the incorporation of optically active chiral amino esters as pendants leads to polymeric products with helical rotating backbones, as revealed by their circular dichroism spectra in the solutions and as cast films. With fluorescent tetraphenylethene moieties embedded in the polymer chains, the polymers display a phenomenon of aggregation-enhanced emission. They emit weakly in the solution state, but fluoresce intensely as aggregates. Moreover, the thin films of the polymers exhibit high light refractivity (n = 1.9305–1.5992) in a wide wavelength region (400–1000 nm), which can be readily modulated by UV irradiation. Additionally, the polymeric products with photosensitivity can generate highly resolved two-dimensional luminescent patterns by UV treatment.

Metal-Free Poly-Cycloaddition of Activated Azide and Alkynes toward Multifunctional Polytriazoles: Aggregation-Induced Emission, Explosive Detection, Fluorescent Patterning, and Light Refraction

The metal-free click polymerization (MFCP) of activated alkynes and azides or activated azide and alkynes have been developed into powerful techniques for the construction of polytriazoles without the obsession of metallic catalyst residues problem. However, the MFCP of activated azides and alkynes is rarely applied in preparation of functional polytriazoles. In this paper, soluble multifunctional polytriazoles (PIa and PIb) with high weight-average molecular weights (Mw up to 32 000) are prepared via the developed metal-free poly-cycloaddition of activated azide and alkynes in high yields (up to 90%). The resultant PIa and PIb are thermally stable, and show aggregation-induced emission characteristics, enabling their aggregates to detect explosives with superamplification effect. Moreover, thanks to their containing aromatic rings and polar moieties, PIa and PIb exhibit high refractive indices. In addition, they can also be cross-linked upon UV irradiation to generate 2D fluorescent patterning due to their remaining azide groups and containing ester groups. Thus, these multifunctional polytriazoles are potentially applicable in the optoelectronic and sensing fields.