Metal-Free Synthesis and Photophysical Properties of 1,2,4-Triarylpyrroles

Copper-catalyzed three-component annulation toward pyrroles via the cleavage of two C-C bonds in 1,3-dicarbonyls

The first copper-catalyzed three-component annulation of α,β-unsaturated ketoximes, 1,3-dicarbonyls and paraformaldehyde has been documented. This novel strategy achieved the two C-C bond cleavage of 1,3-dicarbonyl compounds directly as a single-carbon synthon and provided a new and highly efficient method for the synthesis of 2,3-disubstituted pyrroles in moderate to good yields with broad functional group compatibility.

Blue Emission of Tetrafluorobenzocarbazole Under the Interactions of Nitrogen–oxygen Saturated hydrogen Bonds with Aggregated Proton Acid

Two novel tetrafluorobenzocarbazole and containing the amino branch introduced at the end of the molecule are synthesized by a simple method. The tetrafluorobenzocarbazole as the electron donor with electron-rich fluoride ions connected by π-benzyl ring conjugation structure, which affects the overall electron cloud density. Moreover, the amino branch introduced at the end of the molecule, which makes it easy to form intermolecular hydrogen bonds and affected photophysical properties. Meanwhile, the photophysical property of both compounds are discussed under different acidic conditions. The UV-absorption show that around ~286 nm is mainly attributed to the strong structural absorption band peak of the π-π ∗ transition of the carbazole moiety, and the irregular absorption band around ~314 nm and ~326 nm are mainly attributed to the n-π ∗ transition of the carbazole group conjugate with the adjacent molecule. The emission spectrum of both compounds showed that the intensity of fluorescence decreased in different degrees after the addition of the acidic solution. Furthermore, the electrochemical properties were evidenced by cyclic voltammetry (CV) and density functional theory (DFT) calculations, and the orbital conformation (HOMOs-LUMOs) was simulated by Gaussian 09 software and its crystal structure was observed by X-ray diffraction (XRD). The results exhibited that both compounds are electrochemically stable blue small-molecule fluorescent substances, and expected that both compounds can be novel and stable acid-sensitive organic blue-light materials.

Synthesis of Pyrrole via Formal Cycloaddition of Allyl Ketone and Amine under Metal-Free Conditions

A new metal-free synthesis of pyrrole from allyl ketone and amine has been established. The reaction proceeds via an thiolative activation of the C-C double bond with dimethyl(methylthio)sulfonium trifluoromethanesulfonate, followed by a nucleophilic ring-opening addition of primary amine to the generated episulfonium intermediate, and then an internal condensation and aromatization. This mild procedure provides a novel strategy to the construction of substituted pyrroles through a formal [4 + 1] cycloaddition reaction.

Aromaticity-Enhanced pH-Responsive Electrochemiluminescence of Cyclopentadienols

Due to significantly tackling the problems of aggregation-caused quenching and water insolubility, aggregation-induced emission electrochemiluminescence (AIE-ECL) has emerged as a research highlight in aqueous detection and sensing. Herein, we reported a series of cyclopentadienols featuring excellent AIE-ECL properties on the basis of an enhanced aromaticity strategy. In detail, substituents profoundly determined ECL emission by affecting the characteristic absorption peak intensity ratio in UV-vis spectra and lowest unoccupied molecular orbital (LUMO)-highest occupied molecular orbital (HOMO) energies. It was found that 1,2,3,4,5-pentafluorophenyl cyclopentadienol (PFCD) containing an electron-withdrawing fluorine substituent, the maximum R/B band ratio, and a smaller LUMO-HOMO band gap demonstrated the best ECL performance. Meanwhile, such an AIE-ECL system displayed a wide response range toward pH (4-12) with a good linear relationship. Our research not only enriched polycyclic aromatic hydrocarbon-based AIE-ECL systems but also established an efficient pH sensor in the aqueous phase.

A comprehensive survey upon diverse and prolific applications of chitosan-based catalytic systems in one-pot multi-component synthesis of heterocyclic rings

Heterocyclic compounds are among the most prestigious and valuable chemical molecules with diverse and magnificent applications in various sciences. Due to the remarkable and numerous properties of the heterocyclic frameworks, the development of efficient and convenient synthetic methods for the preparation of such outstanding compounds is of great importance. Undoubtedly, catalysis has a conspicuous role in modern chemical synthesis and green chemistry. Therefore, when designing a chemical reaction, choosing and or preparing powerful and environmentally benign simple catalysts or complicated catalytic systems for an acceleration of the chemical reaction is a pivotal part of work for synthetic chemists. Chitosan, as a biocompatible and biodegradable pseudo-natural polysaccharide is one of the excellent choices for the preparation of suitable catalytic systems due to its unique properties. In this review paper, every effort has been made to cover all research articles in the field of one-pot synthesis of heterocyclic frameworks in the presence of chitosan-based catalytic systems, which were published roughly by the first quarter of 2020. It is hoped that this review paper can be a little help to synthetic scientists, methodologists, and catalyst designers, both on the laboratory and industrial scales.

Aggregation-Induced Emission: From Small Molecules to Polymers-Historical Background, Mechanisms and Photophysics

The enhancement of photoluminescence through formation of molecular aggregates in organic oligomers and conjugated organic polymers is reviewed. A historical contextualization of aggregation-induced emission (AIE) phenomena is presented. This includes the loose bolt or free rotor effect and J-aggregation phenomena, and discusses their characteristic features, including structures and mechanisms. The basis of both effects is examined in key molecules, with a particular emphasis on the AIE effect occurring in conjugated organic polymers with a polythiophene (PT) skeleton with triphenylethylene (TPE) units. Rigidification of the excited state structure is one of the defining conditions required to obtain AIE, and thus, by changing from a flexible ground state to rigid (quinoidal-like) structures, oligo and PTs are among the most promising emerging molecules alongside with the more extensively used TPE derivatives. Molecular structures moving away from the domination of aggregation-caused quenching to AIE are presented. Future perspectives for the rational design of AIEgen structures are discussed.