Haoke Zhang

Axial chiral aggregation-induced emission luminogens with aggregation-annihilated circular dichroism effect

Axial chiral aggregation-induced emission (AIE) luminogens of (R)-3,3′-BTPE-BINA, (R)-6,6′-BTPE-BINA and (S)-6,6′-BTPE-BINA were synthesized for the first time by covalently attaching the AIE-active tetraphenylethene (TPE) units to the axial chiral binaphthol (BINOL) moieties at their 3,3′- or 6,6′-positions. It was found that the circular dichroism (CD) value when TPE was attached to BINOL at its 3,3′-positions was much larger than that found after its attachment at 6,6′-positions. The resultant AIE-active luminogens (AIEgens) show high quantum yields (up to 42.4%) in their aggregated states. Interestingly, these AIEgens exhibit an abnormal aggregation-annihilation CD (AACD) phenomenon. The decrease in the twisted angle between the two naphthalene rings upon aggregation was rationalized as the cause of this unique effect.

Non-conventional fluorescent biogenic and synthetic polymers without aromatic rings

Non-conventional fluorescent materials without aromatic structures have attracted much research attention in recent years. However, the working mechanism responsible for their fluorescence remains mysterious. Here we decipher the origin of fluorescence by studying the photophysical properties of a series of non-aromatic biogenic and synthetic peptides. An experimental study suggests that the turn-on fluorescence in the aggregation state/condensed phase is associated with the communication of amide groups, where hydrogen bonds are playing a critical role in bringing these functionalities into close proximity. This explanation is further justified by the study of the hierarchical influence on fluorescence and applied to biomimetic polymers in a more general content. This discovery provides a more comprehensive insight into the bioluminescence system. It may stimulate future development of new fluorescent materials, and inspire research on disease diagnostics, biomechanics measurements, etc. that are associated with protein morphology.

In Situ Monitoring of RAFT Polymerization by Tetraphenylethylene‐Containing Agents with Aggregation‐Induced Emission Characteristics

A facile and efficient approach is demonstrated to visualize the polymerization in situ. A group of tetraphenylethylene (TPE)-containing dithiocarbamates were synthesized and screened as agents for reversible addition fragmentation chain transfer (RAFT) polymerizations. The spatial-temporal control characteristics of photochemistry enabled the RAFT polymerizations to be ON and OFF on demand under alternating visible light irradiation. The emission of TPE is sensitive to the local viscosity change owing to its aggregation-induced emission characteristic. Quantitative information could be easily acquired by the naked eye without destroying the reaction system. Furthermore, the versatility of such a technique was well demonstrated by 12 different polymerization systems. The present approach thus demonstrated a powerful platform for understanding the controlled living radical polymerization process.

Facile Multicomponent Polymerizations toward Unconventional Luminescent Polymers with Readily Openable Small Heterocycles

Heterocyclic polymers have gained enormous attention for their unique functionalities and wide applications. In contrast with the well-studied polymer systems with five- or six-membered heterocycles, functional polymers with readily openable small-ring heterocycles have rarely been explored due to their large synthetic difficulty. Herein, a facile one-pot multicomponent polymerization to such polymers is developed. A series of functional polymers with multisubstituted and heteroatom-rich azetidine frameworks are efficiently generated at room temperature in high atom economy from handy monomers. The four-membered azetidine rings in the polymer skeletons can be easily transformed into amide and amidine moieties via a fast and efficient acid-mediated ring-opening reaction, producing brand-new polymeric materials with distinctive properties. All the as-prepared azetidine-containing polymers exhibit intrinsic visible luminescence in the solid state under long-wavelength UV irradiation even without conventionally conjugated structures. Such unconventional luminescence is attributed to the clusteroluminogens formed by through-space electronic interactions of heteroatoms and phenyl rings. All the obtained polymers show excellent optical transparency, high and tunable refractive indices, low optical dispersions and good photopatternability, which make them promising materials in various advanced electronic and optoelectronic devices. The ring-opened polymers can also function as a lysosome-specific fluorescent probe in biological imaging.

3,4,5-Triphenyl-1,2,4-triazole-based multifunctional n-type AIEgen

The luminogens with aggregation-induced emission (AIEgens) characteristics have been widely applied in diverse areas. However, the n-type AIEgens are to be further developed. In this paper, we designed and synthesized an n-type multifunctional AIEgen of tetraphenylethene-substituted 3,4,5-triphenyl-4H-1,2,4-triazole (BTPE-TAZ). This AIEgen can serve as both light-emitting and electron-transporting layers in organic light-emitting devices. Moreover, it also exhibits the interesting optical waveguide and reversible mechanochromic luminescence properties, which are of great potential for practical applications.

Multiple Stimuli Responses of Stereo-Isomers of AIE-Active Ethynylene-Bridged and Pyridyl-Modified Tetraphenylethene

Luminescent molecules with aggregation-induced emission (AIE) property or AIE-active luminogens (AIE-gens) are typical stimuli-responsive materials. Many AIE-gens have shown luminescent responses to mechano-, thermo-, electro-, vapo-, and/or solvato-stimulus, but the detailed structure-property relationship has been addressed for only a few of them. Here, we report a tetraphenylethene (TPE) derivative with pyridyl modifiers and ethynylene bridges. The (Z)- and (E)-isomers are clearly purified, and both of them are AIE-active and demonstrate multiple luminescent responses to external stimuli. Distinct from other reported TPE derivatives, the two isomers show negative solvatochromism due to the large dipole in the ground electronic state. By correlating with the single crystal structures, the subtle differences in quantum efficiency and emission peak wavelength of the solids of the (Z)- and (E)-isomers are rationally explained. Moreover, the ground powder of the (E)-isomer can recover its emission color from green to blue in the air at room temperature but the (Z)-isomer cannot. This difference is interpreted by a mechanism of water-triggered conformational variation, which depends on the hydrogen bond formation between pyridyl moieties and water molecules in the air. In addition to the reversible emission color changes by cyclic grinding-fuming treatments, both of the isomers exhibit a reversible luminescent response to acid-base treatments by switching the emission color between green (basic) and yellow (acid), owing to the incorporation of pyridyl units into the molecule. The unprecedented multiple stimuli-responsive behaviors and clear mechanism explanations allow this kind of AIE-gens to be promising smart materials.

Unveiling the Different Emission Behavior of Polytriazoles Constructed from Pyrazine-Based AIE Monomers by Click Polymerization

Polymers with aggregation-induced emission (AIE) characteristics have aroused tremendous interest because of their potential applications in large-area flexible display and luminescent self-assembling, and as stimuli-responsive and porous materials. However, the design of AIE-active polymers is always not as easy as that of small molecules because their properties are hard to predict. In some cases, the polymers prepared from the AIE-active monomers show the aggregation-caused quenching (ACQ) instead of AIE effect. To understand the structure-property relationship of the polymers constructed from the AIE monomers, in this paper, two pyrazine-containing AIE monomers were utilized to construct luminescent polymers by click polymerization. The photophysical property investigation indicates that the polytriazole containing tetraphenylpyrazine units is AIE-active, whereas that bearing 2,3-dicyano-5,6-diphenylpyrazine units suffers from the ACQ effect. Through systematical investigation, the cause for such difference was unveiled. Thus, this work provides a useful guidance for further design of AIE-active polymers.