Wang Zhang Yuan

Changing the Behavior of Chromophores from Aggregation‐Caused Quenching to Aggregation‐Induced Emission: Development of Highly Efficient Light Emitters in the Solid State

The development of efficient luminescent materials in the solid state is of both scientific and technological interest. An obstacle to their development is the notorious aggregation-caused quenching (ACQ) effect: the emission of conventional luminophores is often weakened in the solid state in comparison to in solution, due to aggregate formation in the condensed phase. [1‐3] The ACQ problem must be properly tackled, because the luminophores are commonly used as solid films in their practical applications. Various chemical, physical, and engineering approaches have been taken to frustrate luminophore aggregation. [4,5] The attachment of bulky alicyclics, encapsulation by amphiphilic surfactants, and blending with transparent polymers are widely used methods to impede aggregate formation. These processes, however, are often accompanied by severe side effects. The steric effects of bulky alicyclics, for example, can twist the conformations of the chromophoric units and jeopardize the electronic conjugation in the luminophores, and the electronic effects of the saturated surfactants and nonconjugated polymers can dilute the luminophore density and obstruct the charge transport in electroluminescence (EL) devices. The current approaches to the problem are thus far from ideal, because the ACQ effect is alleviated at the expense of other useful properties of the luminophores. A win‐win strategy would be the elimination of the ACQ effect without sacrificing other functional properties of the luminophores. In the work reported here, we have developed such a new approach. Triphenylamine (TPA) and its derivatives are luminescent when dissolved in good solvents [6] for them but become less emissive when aggregated in the solid state, and are therefore typical ACQ luminophores. [7] For

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.

Achieving Persistent Room Temperature Phosphorescence and Remarkable Mechanochromism from Pure Organic Luminogens

Persistent room temperature phosphorescence (RTP) from pure organic luminogens can be rationally realized based on the crystallization-induced phosphorescence phenomenon and severe crystallization. A perfect crystal with dense molecular packing and effective inter-molecular interactions isolates the triplet excitons from quenching sites and significantly blocks the high-energy vibrational dissipation, thus yielding long-lasting RTP.

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.

Aggregation-Induced Emission in a Hyperbranched Poly(silylenevinylene) and Superamplification in Its Emission Quenching by Explosives.

A silicon-containing hyperbranched polymer (hb-P1/2) with σ*-π* conjugation was prepared in a good yield and high molecular weight by rhodium-catalyzed alkyne polyhydrosilylation of 1,2-bis(4-ethynylphenyl)-1,2-diphenylethene (1) with tris(4-dimethylsilylphenyl)amine (2). The polymer was thermally stable, losing merely 5% of its weight when heated to ≈445 °C. Whereas hb-P1/2 was weakly luminescent when molecularly dissolved, it became highly emissive when supramolecularly aggregated, showing an aggregation-induced emission (AIE) phenomenon. A superamplification effect was observed when the AIE nanoaggregates were used as fluorescent chemosensor for explosive detection: the quenching efficiency was greatly increased in a nonlinear fashion with increasing quencher concentration.

Conjugation‐Induced Rigidity in Twisting Molecules: Filling the Gap Between Aggregation‐Caused Quenching and Aggregation‐Induced Emission

Conjugation-induced rigidity in twisting molecules provides a new facile but effective avenue toward solution and solid dual-state efficient luminogens. While conjugation rigidifies the molecular conformations in solution, the twisting structure prevents or alleviates detrimental close molecular packing in the solid states, thus synergistically yielding high efficiencies in both solution and solid states.

Diethylamino functionalized tetraphenylethenes: structural and electronic modulation of photophysical properties, implication for the CIE mechanism and application to cell imaging

Deciphering structural and electronic effects on photophysical properties of aggregation- or crystallization-induced emission (AIE or CIE) luminogens is essential to the related mechanistic understanding, molecular design and applications. Herein, based on AIE-active tetraphenylethene (TPE), a group of diethylamino (DEA) functionalized analogues, i.e. DEATPE, DFDEATPE and CNDEATPE were designed and prepared. The introduction of DEA groups makes DEATPE CIE-active rather than typically AIE-active. Further incorporation of fluorine atoms renders DFDEATPE with AIE and crystallization-induced emission enhancement (CIEE) characteristics. Furthermore, unlike the nonmechanochromic TPE, these luminogens exhibit high contrast mechanochromism. Specifically, DEATPE and DFDEATPE demonstrate rapid self-recovery within a few minutes or even several seconds. Such swift restoration of solid emission clearly indicates active intramolecular motions even in the solid states, which is indicative of the CIE mechanism. Additionally, luminogenic nanoparticles were successfully utilized in cell imaging, thanks to their high efficiency and biocompatibility.

Conjugated Hyperbranched Poly(aryleneethynylene)s: Synthesis, Photophysical Properties, Superquenching by Explosive, Photopatternability, and Tunable High Refractive Indices

Triphenylamine (TPA)-based conjugated hyperbranched poly(aryleneethynylene)s (PAEs), hb-P1/2, hb-P1/3, and hb-P1/4, were synthesized with high molecular weights and good solubilities through Sonogashira coupling reactions. These PAEs exhibited outstanding thermal stabilities and different emission behaviors. Tetraphenylethene (TPE)-containing hb-P1/2 fluoresced faintly in THF, although its light emission was enhanced by aggregate formation in aqueous media or in thin films, thereby exhibiting an aggregation-induced emission-enhancement (AIEE) effect. Whereas 1,1,2,3,4,5-hexaphenylsilole (HPS)-bearing hb-P1/3 showed no significant change in emission intensity with increasing water content in aqueous media, hb-P1/4, which consisted of TPA-fluorenone donor-acceptor groups, presented almost identical absorptions, but both positive and negative solvatochromic emissions in various solvents. A superquenching effect was observed in the picric-acid-detection process by using nanosuspensions of hb-P1/2. All of the polymers possessed good film formability. UV irradiation of the thin films induced simultaneous photobleaching and cross-linking, thus making them applicable in the fabrication of 2D and 3D patterns. Furthermore, the polymer films also showed high refractive indices, which were tunable upon exposure to UV light.