Jing Zhi Sun

Click Synthesis, Aggregation-Induced Emission, E/Z Isomerization, Self-Organization, and Multiple Chromisms of Pure Stereoisomers of a Tetraphenylethene-Cored Luminogen

It has been difficult to decipher the mechanistic issue whether E/Z isomerization is involved in the aggregation-induced emission (AIE) process of a tetraphenylethene (TPE) derivative, due to the difficulty in the synthesis of its pure E and Z conformers. In this work, pure stereoisomers of a TPE derivative named 1,2-bis{4-[1-(6-phenoxyhexyl)-4-(1,2,3-triazol)yl]phenyl}-1,2-diphenylethene (BPHTATPE) are successfully synthesized. Both isomers show remarkable AIE effect (α(AIE) ≥ 322) and high fluorescence quantum yield in the solid state (Φ(F) 100%). The conformers readily undergo E/Z isomerization upon exposure to a powerful UV light and treatment at a high temperature (>200 °C). Such conformational change, however, is not observed under normal fluorescence spectrum measurement conditions, excluding the involvement of the E/Z isomerization in the AIE process of the TPE-based luminogen. The molecules of (E)-BPHTATPE self-organize into ordered one-dimensional nanostructures such as microfibers and nanorods that show obvious optical waveguide effect. BPHTATPE shows rich chromic effects, including mechano-, piezo-, thermo-, vapo-, and chronochromisms. Its emission peak is bathochromically shifted by simple grinding and pressurization and the spectral change is reversed by fuming with a polar solvent, heating at a high temperature, or storing at room temperature for some time. The multiple chromic processes are all associated with changes in the modes of molecular packing.

Switching the light emission of (4-biphenylyl)phenyldibenzofulvene by morphological modulation: crystallization-induced emission enhancement

(4-Biphenylyl)phenyldibenzofulvene is weakly luminescent in the amorphous phase but becomes highly emissive upon crystallization; this unusual crystallization-induced emission enhancement effect allows its emission to be repeatedly switched between dark and bright states by fuming-heating and heating-cooling processes.

Synergy between Twisted Conformation and Effective Intermolecular Interactions: Strategy for Efficient Mechanochromic Luminogens with High Contrast

A strategy towards efficient mechanochromic luminogens with high contrast is developed. The twisted propeller-like conformations and effective intermolecular interactions not only endow the luminogens with AIE characteristics and high efficiency in the crystalline state, but also render them to undergo conformational planarization and disruption in intermolecular interactions upon mechanical stimuli, resulting in remarkable changes in emission wavelength and efficiency.

Hyperbranched polytriazoles with high molecular compressibility: aggregation-induced emission and superamplified explosive detection

Hyperbranched polytriazoles with spring-like architectures exhibit the feature of aggregation-induced emission (AIE) due to the high compressibility of polymer spheres from solution to aggregate. Thanks to their AIE effect, the polymer nanoaggregates can detect explosives with superamplification effect.

Aggregation-induced red-NIR emission organic nanoparticles as effective and photostable fluorescent probes for bioimaging

Organic fluorescent probes are widely used in bioimaging and bioassays, but the notorious photobleaching hampers their applications. Encapsulation of organic dyes into nanoparticles (NPs) is an effective strategy to minimize photobleaching, but classical organic dye molecules tend to have their fluorescence quenched in aggregate states, which is termed aggregation-caused quenching (ACQ). Here we demonstrate our attempt to tackle this problem through the aggregation-induced emission (AIE) strategy. 3,4:9,10-Tetracarboxylic perylene bisimide (PBI) is a well-known organic dye with a serious ACQ problem. By attaching two tetraphenylethene (TPE) moieties to the 1,7-positions, the ACQ-characteristic PBI-derivative was converted to an AIE-characteristic molecule. The obtained PBI derivative (BTPEPBI) exhibits several advantages over classical PBI derivatives, including pronounced fluorescence enhancement in aggregate state, red to near infrared emission, and facile fabrication into uniform NPs. Studies on the staining of MCF-7 breast cancer cells and in vivo imaging of a tumor-bearing mouse model with BTPEPBI-containing NPs reveal that they are effective fluorescent probes for cancer cell and in vivo tumor diagnosis with high specificity, high photostability and good fluorescence contrast.

A pyridinyl-functionalized tetraphenylethylene fluorogen for specific sensing of trivalent cations.

A pyridinyl-functionalized tetraphenylethene (Py-TPE) was synthesized and it demonstrated colorimetric and ratiometric fluorescent responses to trivalent metal cations (M(3+), M = Cr, Fe, Al) over a variety of mono- and divalent metal cations.

A fluorescent thermometer operating in aggregation-induced emission mechanism: probing thermal transitions of PNIPAM in water

Poly(N-isopropylacrylamide) was labelled using a fluorogen with an aggregation-induced emission feature by direct polymerization; the label served as a fluorogenic probe that reveals fine details in the thermal transitions in the aqueous solution of the polymer; the working mode was readily tuned between non-monotonic and monotonic by changing the labelling degree of the polymer.

Siloles symmetrically substituted on their 2,5-positions with electron-accepting and donating moieties: facile synthesis, aggregation-enhanced emission, solvatochromism, and device application

Three dimethyltetraphenylsiloles (DMTPSs) symmetrically substituted on their 2,5-positions with electron-accepting (A), i.e.aldehyde (ALD) and dicyanovinyl (DCV) or donating (D), i.e.diphenylamine (DPA) moieties were designed and synthesized via facile reaction procedures. The propeller-shaped luminogens exhibit aggregation-induced/enhanced emission characteristics with high quantum yields up to 74.0% in the solid state, and are thermally stable, showing high degradation temperatures and melting points up to 388 and 246 °C, respectively. Thanks to the contained A or D moieties, the siloles show intriguing solvatochromism: DMTPS-ALD exhibits almost no response to solvents due to the balance of electron affinities of the aldehyde and the silole core. Whereas, DMTPS-DCV and DMTPS-DPA possess outward intramolecular charge-transfer (ICT) from the silole core and the phenyl rings on its 3,4-positions to dicyanovinyl groups, and inward ICT from diphenylamine groups to the silole core, respectively, showing positive solvatochromism. A multilayer organic light-emitting diode using DMTPS-DPA among the luminogens as an emitter layer shows the highest performance with turn-on voltage, maximum luminance, current, power, and external efficiencies of 3.1 V, 13405 cd m−2, 8.28 cd A−1, 7.88 lm W−1, and 2.42%, respectively. Furthermore, DMTPS-DPA can also serve in hole-transporting layers because of its high hole-mobility. Therefore, the incorporation of a triphenylamine moiety into a silole system not only changes the classical aggregation-caused quenching fluorophore into AEE-active DMTPS-DPA, another example of “turning stone into gold”, but also enhances the hole-transporting ability of siloles.

A facile room-temperature chemical reduction method to TiO2@CdS core/sheath heterostructure nanowires

We have prepared functional TiO2@CdS core/sheath heterostructure nanowires using a simple chemical reduction method at room temperature. The core/sheath nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-visible spectroscopic techniques. It was found that the thickness of the CdS sheath could be controlled by the concentration of the precursors. The continuous and polycrystalline CdS outer layer could be formed on the TiO2 nanowires when the concentration of the S precursor was higher than 0.2 mmol. A possible multi-site growth mechanism of the formation of the composite nanowires was proposed.

Azide-alkyne click polymerization: An update

The great achievements of click chemistry have encouraged polymer scientists to use this reaction in their field. This review assembles an update of the advances of using azide-alkyne click polymerization to prepare functional polytriazoles (PTAs) with linear and hyperbranched structures. The Cu(I)-mediated click polymerization furnishes 1,4-regioregular PTAs, whereas, the metal-free click polymerization of propiolates and azides produces PTAs with 1,4-regioisomer contents up to 90%. The PTAs display advanced functions, such as aggregation-induced emission, thermal stability, biocompatibility and optical nonlinearity.