Synthetic Regulation of 1,4-Dihydropyridines for the AIE or AIEE Effect: From Rational Design to Mechanistic Views

Chemoselective Condensation of 3-Amino-2-cyclohexenones with Cinnamaldehydes: Switchable Synthesis of Dihydroquinolinones and Hexahydroacridinediones

Herein, a chemoselective condensation of 3-amino-2-cyclohexenones and cinnamaldehydes for switchable synthesis of dihydroquinolinones and hexahydroacridinediones was developed. Mechanism analysis showed that the formation of dihydroquinolinones involved trimolecular condensation and oxidative aromatization, while the formation of hexahydroacridinediones involved acid hydrolysis of enaminone and dehydration-aromatization. This strategy provides a convenient way to switch from the same substrates to produce two different quinolinone derivatives.

Ultrastrong Red Circularly Polarized Luminescence Promoted from Chiral Transfer and Intermolecular Förster Resonance Energy Transfer in Ternary Chiral Emissive Nematic Liquid Crystals

Chiral emissive liquid crystals (N*-LCs) have been proved to greatly amplify the circularly polarized luminescence (CPL) signals due to highly regular spiral arrangement of dyes in a well-organized liquid crystals system. Normally, CPL materials with a high luminescence dissymmetry factor (g_lum) and quantum yield (QY) can meet the real application requirement. Here, four chiral aggregate-induced emission (AIE) active donors (Guests A1-A4: R-C2, R-C4, R-C6, R-C8, chiral dopant, and energy donor) and achiral AIE-active acceptors (Guest B: PBCy, CPL emitter) were doped into the commercial nematic liquid crystals E7 (N-LCs, Host) to form CPL-active ternary chiral emissive N-LCs (T-N*-LCs), respectively. This kind of T-N*-LCs could emit strong red CPL with QY = 16.56% and g_lum up to 1.51 through intermolecular energy transfer and chirality induction from the supramolecular self-assembly of T-N*-LCs. This work provides the effective strategy for the development of high g_lum CPL materials.

Enzyme-catalysed one-pot synthesis of 4H-pyrimido[2,1-b] benzothiazoles and their application in subcellular imaging

Enzymes, which provide more efficient and eco-friendly strategies for various functional molecules' construction than traditional chemo-catalysts, were utilized for the synthesis of 4H-pyrimido[2,1-b] benzothiazole derivatives. Reported herein is a trypsin-catalysed three- component Biginelli reaction of aldehyde, β-ketoester and 2-amino benzothiazole in one pot, affording a streamlined pathway to diverse ring-fused pyrimidines. In addition to using commercially available aromatic aldehydes as substrates, acetaldehyde, the chemical liquid with rather low boiling point and difficult to handle above room temperature, is utilized to further extend the range of substrates. It was verified that most of the tested substrates exhibited satisfactory reactivity. In addition, several substrates indicated AIE (Aggregation-Induced Emission) property and have been investigated as potential biomarkers.

Combining photo-redox and enzyme catalysis for the synthesis of 4H-pyrimido[2,1-b] benzothiazole derivatives in one pot

A novel strategy combining visible-light and enzyme catalysis in one pot for the synthesis of 4H-pyrimido[2,1-b] benzothiazole derivatives from alcohols is described for the first time. Fourteen 4H-pyrimido[2,1-b] benzothiazole derivatives were prepared with yields of up to 98% under mild reaction conditions by a simple operation. The photoorgano catalyst rose Bengal (rB) was employed to oxyfunctionalise alcohols to aldehydes. Compared with aldehydes, alcohols with more stable properties and lower cost, thus we used photocatalysis to oxidize alcohols into aldehydes. Next, the enzyme was used to further catalyze the reaction of Biginelli to produce the target product of 4H-pyrimidine [2,1-b] benzothiazole. Experimental results show that this method provides a more efficient and eco-friendly strategy for the synthesis of 4H-pyrimido[2,1-b] benzothiazole derivatives.

Restriction of Conformation Transformation in Excited State: An Aggregation-Induced Emission Building Block Based on Stable Exocyclic C=N Group

The development of aggregation-induced emission (AIE) building block and deciphering its luminescence mechanism are of great significance. Here a feasible strategy for the construction of AIE unit based on E-Z isomerization (EZI) of exocyclic C=N double bond is proposed. Taking [1,2,4]thiadiazole[4,3-a]pyridine (TZP) derivative as an example, its aryl-substituted derivative (TZPP) shows obvious AIE character. The analysis of spectral data and theoretical calculations indicates that fast structural relaxation of TZPP in the emissive state plays a key role in a low fluorescence quantum yield in dilute solution, which should be caused by the small energy gap between locally excited (LE) state and twisted intramolecular charge transfer state. When in solid state, the bright emission with LE state characteristic reappears due to the large shift barrier of geometry transformation. As a potential building block for AIEgens with special heterocyclic structure, these findings would open up opportunities for developing various functional materials.

•

A new aggregation-induced emission building block

•

A novel AIE mechanism with spectral measurements and theoretical calculations

•

Available starting materials resulting in convenient synthesis and modification

•

A stable exocyclic C=N double bond in heterocycles

Deciphering the Dynamics of Organic Nanoaggregates with AIEE Effect and Excited States: Lipophilic Benzothiadiazole Derivatives as Selective Cell Imaging Probes

An aggregation-induced emission enhancement (AIEE) effect in fluorescent lipophilic 2,1,3-benzothiadiazole (BTD) derivatives and their organic nanoaggregates were studied. A set of techniques such as single-crystal X-ray, dynamic light scattering (DLS), electron paramagnetic resonance (EPR), UV-vis, fluorescence, and density functional theory (DFT) calculations have been used to decipher the formation/break (kinetics), properties, and dynamics of the organic nanoaggregates of three BTD small organic molecules. An in-depth study of the excited-state also revealed the preferential relaxation emissive pathways for the BTD derivatives and the dynamics associated with it. The results described herein, for the first time, explain the formation of fluorescent BTD nanoaggregate derivatives and allow for the understanding of their dynamics in solution as well as the ruling forces of both aggregation and break processes along with the involved equilibrium. One of the developed dyes could be used at a nanomolar concentration to selectively stain lipid droplets emitting an intense and bright fluorescence at the red channel. The other two BTDs could also stain lipid droplets at very low concentrations and were visualized preferentially at the blue channel.

Aggregation-Induced Emission Probes for Specific Turn-On Quantification of Bovine Serum Albumin

A series of aggregation-induced emission (AIE) fluorescence probes, coined 4H-pyrimido[2,1-b]benzothiazole derivatives, has been synthesized by Biginelli reactions. Utilizing spectroscopic techniques, their photophysical properties have been comprehensively investigated in working environment both in vitro and in vivo. Density functional theory (DFT) calculations were performed to better understand the mechanism of these probes. The interactions between 4H-pyrimido[2,1-b]benzothiazoles with different substituents and bovine serum albumin (BSA) were analyzed using UV-vis and fluorescence spectroscopy, synchronous fluorescence, and docking analysis. Studies found that 4H-pyrimido[2,1-b]benzothiazole could bind to bovine serum albumin (BSA) through a hydrogen bond and hydrophobic interactions, resulting in enhancement of fluorescence emission of probes 1a-6f and fluorescence quenching of BSA. Combined with cell imaging experiments, these provide information on potential effects of benzothiazoles on disease treatment.

Tetraphenylethylene conjugated p-hydroxyphenacyl: fluorescent organic nanoparticles for the release of hydrogen sulfide under visible light with real-time cellular imaging

Hydrogen sulfide (H2S) behaves like a two-edged sword, at low concentrations it has beneficial and cytoprotective effects, while at higher concentrations it exhibits toxicity. Hence there is a keen interest in developing light responsive H2S donors with a spatio-temporal controlled release. Herein, we report visible light activatable tetraphenylethylene conjugated p-hydroxyphenacyl (TPE-pHP-H2S) nanoparticles for the release of hydrogen sulfide (H2S) with a real time monitoring ability. Our newly designed photoresponsive single component organic nanoparticle based H2S donor is built by integrating the tetraphenylethylene (TPE) moiety and p-hydroxyphenacyl (pHP) group so that it can display both aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT) properties. Aggregation-induced emission enhancement was exhibited by our TPE-pHP-H2S NP donor, which was then explored for the cellular imaging application. The ESIPT by the pHP moiety provided unique advantages to our TPE-pHP-H2S NP donor which include (i) the excitation wavelength extended to >410 nm (ii) a large Stokes shift (iii) a low inner filter effect and (iv) real-time monitoring of H2S release by a simple fluorescent colour change. In vitro studies showed that the TPE-pHP-H2S NP donor presents excellent properties like real-time monitoring, photoregulated H2S release and biocompatibility.

Photophysics of proton transfer in hydrazides: a combined theoretical and experimental analysis towards OLED device application

Effect of conjugation to support ESIPT with impossible double proton transfer in structurally favored species.

A two-stage assembly with PEI induced emission enhancement of Au-AgNCs@AMP and the intrinsic mechanism

Recently, aggregation-induced emission (AIE) properties have been revealed for some metal nanoclusters (NCs), providing a new approach to improve the quantum yields (QY). In the present study, a two-stage assembly was carried out between adenosine monophosphate capped bimetallic nanoclusters of gold and silver (Au-AgNCs@AMP) and polyethylenimine (PEI), in which the QY was improved from 8.64% to 25.02%, showing obvious assembly induced emission enhancement (AIEE) properties. The intrinsic mechanisms of the assembly and emission enhancement in two stages were studied in depth, which indicated that the electrostatic interaction between the phosphate group in AMP and the amino group in PEI restricted the intramolecular vibration and rotation of capping ligands, and reduced the non-radiative relaxation of the corresponding excited states in stage I; in stage II, the micellization of PEI at high concentration pushed the NCs into a less polar environment and greatly enhanced the metal-metal interaction between them, which facilitated the excited state relaxation dynamics via a radiative pathway. Therefore, the luminescence enhancement depended on the assembly process in two stages directly. The present study is beneficial to understand the AIEE mechanism and the design principles, which will expand the applications of metal NCs.