Zikai He

A Ratiometric Fluorescent Probe Based on ESIPT and AIE Processes for Alkaline Phosphatase Activity Assay and Visualization in Living Cells

Alkaline phosphatase (ALP) activity is regarded as an important biomarker in medical diagnosis. A ratiometric fluorescent probe is developed based on a phosphorylated chalcone derivative for ALP activity assay and visualization in living cells. The probe is soluble in water and emits greenish-yellow in aqueous buffers. In the presence of ALP, the emission of probe changes to deep red gradually with ratiometric fluorescent response due to formation and aggregation of enzymatic product, whose fluorescence involves both excited-state intramolecular proton transfer and aggregation-induced emission processes. The linear ratiometric fluorescent response enables in vitro quantification of ALP activity in a range of 0-150 mU/mL with a detection limit of 0.15 mU/mL. The probe also shows excellent biocompatibility, which enables it to apply in ALP mapping in living cells.

White light emission from a single organic molecule with dual phosphorescence at room temperature

The development of single molecule white light emitters is extremely challenging for pure phosphorescent metal-free system at room temperature. Here we report a single pure organic phosphor, namely 4-chlorobenzoyldibenzothiophene, emitting white room temperature phosphorescence with Commission Internationale de l’Éclair-age coordinates of (0.33, 0.35). Experimental and theoretical investigations reveal that the white light emission is emerged from dual phosphorescence, which emit from the first and second excited triplet states. We also demonstrate the validity of the strategy to achieve metal-free pure phosphorescent single molecule white light emitters by intrasystem mixing dual room temperature phosphorescence arising from the low- and high-lying triplet states.The development of single molecule white light-emitters is extremely challenging for pure phosphorescent metal-free systems at room temperature. Here the authors show a single pure organic room temperature phosphor, 4-chlorobenzoyldibenzothiophene, utilizing the emission from both T1 and T2 states.

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.

Polyyne bridged AIE luminogens with red emission: design, synthesis, properties and applications

Construction of a donor-acceptor (D-A) structure and extension of π-conjugation are the commonly used strategies to shift the emission of luminophores to the red region. However, molecules with high conjugation and a strong D-A effect tend to show weak emission due to the severe π-π interactions and twisted intramolecular charge transfer (TICT) effects. The turn-on characteristic of AIE luminogens (AIEgens) will also be lost due to the conjugation-enhanced emission in the solution state. Herein, a polyyne-bridged AIE luminogen (2TPE-4E) with long wavelength absorption and red emission has been afforded. Despite its large π-conjugation, 2TPE-4E suffers from no emission quenching resulted from strong π-π interactions and twisted intramolecular charge transfer effects. The strong red emission and the high photostability of 2TPE-4E inspired us to use it for targeted-imaging of cancer cells and monitoring the receptor mediated endocytosis process.

Journey of Aggregation-Induced Emission Research

Highly efficient luminescent materials in solid states are promising candidates for the development of organic optoelectrical materials and devices and chemical and biological sensors. Aggregation-induced emission (AIE), a novel photophyscial phenomena coined in 2001 where the aggregate formation enhances the light emission, has drawn great attention because it provides a fantastic platform for the development of these useful luminescent materials. After 17 years of AIE research, diverse AIE luminogens with tunable color and high quantum yields have been explored, which finds diverse applications from optics and electronics to energy and bioscience. Most importantly, the concept of AIE has gradually changed people’s thinking way about the aggregation of luminogen and put forth a revolution of luminogen research both conceptually and technically. This perspective revisits our journey of AIE research, discusses our current understanding of the AIE mechanism, debates current challenges, and looks for the potential breakthroughs in this exciting research area.

A Luminescent Nitrogen-Containing Polycyclic Aromatic Hydrocarbon Synthesized by Photocyclodehydrogenation with Unprecedented Regioselectivity

We present a nitrogen-containing polycyclic aromatic hydrocarbon (N-PAH), namely 12-methoxy-9-(4-methoxyphenyl)-5,8-diphenyl-4-(pyridin-4-yl)pyreno[1,10,9-h,i,j]isoquinoline (c-TPE-ON), which exhibits high quantum-yield emission both in solution (blue) and in the solid state (yellow). This molecule was unexpectedly obtained by a three-fold, highly regioselective photocyclodehydrogenation of a tetraphenylethylene-derived AIEgen. Based on manifold approaches involving UV/Vis, photoluminescence, and NMR spectroscopy as well as HRMS, we propose a reasonable mechanism for the formation of the disk-like N-PAH that is supported by density functional theory calculations. In contrast to most PAHs that are commonly used, our system does not suffer from entire fluorescence quenching in the solid state due to the peripheral aromatic rings preventing π-π stacking interactions, as evidenced by single-crystal X-ray analysis. Moreover, its rod-like microcrystals exhibit excellent optical waveguide properties. Hence, c-TPE-ON comprises a N-PAH with unprecedented luminescent properties and as such is a promising candidate for fabricating organic optoelectronic devices. Our design and synthetic strategy might lead to a more general approach to the preparation of solution- and solid-state luminescent PAHs.

Development of benzylidene-methyloxazolone based AIEgens and decipherment of their working mechanism

Based on an analogue of green fluorescent protein chromophore benzylidene-methyloxazolone (BMO), a series of fluorophores with an additional phenyl group, BMO-PH, BMO-PF, BMO-PM and BMO-PC, have been prepared and are found to be AIE-active. Their solutions are weakly emissive and their aggregation or solid states are highly emissive. Although these compounds readily undergo efficient E/Z isomerization (EZI) upon UV irradiation in solution, the intramolecular rotation around the double bond and phenyl rotation around the single bond serve as the key non-radiative decay channels to dissipate the excited-state energies. The EZI is only the phenomenal result. In aggregates, these intramolecular motions are greatly restricted by multiple intermolecular interactions, resulting in the AIE effect. To ensure a high solid-state quantum yield, prevention of detrimental π–π stacking is of essence. An additional phenyl group to BMO is found to increase the π–π distance and weaken the π–π interaction. Thus, the quantum yields are increased. Strong electron-donating groups and extended conjugation are effective at tuning the emission color bathochromically. Based on these principles, we succeeded in increasing the solid-state quantum yield up to 50% and obtaining a red emission maximum of 635 nm. Moreover, these compounds are promising for applications in photoswitches and fluorescent patterns, and their crystals are good candidates for luminescent waveguides with low light loss efficiency.

Aggregation-Induced-Emission-Active Macrocycle Exhibiting Analogous Triply and Singly Twisted Mobius Topologies

Molecules with Möbius topology have drawn increasing attention from scientists in a variety of fields, such as organic chemistry, inorganic chemistry, and material science. However, synthetic difficulties and the lack of functionality impede their fundamental understanding and practical applications. Here, we report the facile synthesis of an aggregation-induced-emission (AIE)-active macrocycle (TPE-ET) and investigate its analogous triply and singly twisted Möbius topologies. Because of the twisted and flexible nature of the tetraphenylethene units, the macrocycle adjusts its conformations so as to accommodate different guest molecules in its crystals. Moreover, theoretical studies including topological and electronic calculations reveal the energetically favorable interconversion process between triply and singly twisted topologies.