Photo-activated Carbon dots (CDs) as Catalysts in the Knoevenagel Condensation: A Mechanistic Study by Dual-Mode Monitoring via ESI-MS

Carbon dots (CDs) obtained from 5-(hydroxymethyl)furfural (5-HMF) were activated by a 365 nm-UV irradiation source and employed in the Knoevenagel condensation to investigate their photocatalytic mechanism. To this end, electrospray ionization mass spectrometry (ESI-MS) was used to monitor the time progress of the condensation and follow the formation of the final product in positive and negative ion modes at once. The intervention of the superoxide radical anion in the photocatalytic mechanism of CDs was highlighted.

Fully unsaturated all-carbon bifluorenylidene-based polymeric frameworks: synthesis and efficient photocatalysis

Conjugated porous polymers with fully unsaturated all-carbon frameworks possess strong visible light-absorbing abilities, enabling efficient photodegradation of dye pollutants.

Highly Porous Poly(arylene cyano-vinylene) Beads Derived through the Knoevenagel Condensation of the Oil-in-Oil-in-Oil Double Emulsion Templates

Conjugated porous polymers through the emulsion-templating polymerization process are typically prepared as monoliths, and the emulsions are cured via metal-catalyzed cross-coupling reactions. Herein, we report the design and synthesis of well-defined, millimeter-sized conjugated porous polymer beads by combining an oil-in-oil-in-oil (O/O/O) double emulsion as a de novo template and an amino-catalyzed Knoevenagel condensation reaction as a polymerization chemistry to cure such emulsions. The 1,4-phenylenediacetonitrile is reacted with aromatic multialdehydes in the presence of piperidine, and a series of metal-free poly(arylene cyano-vinylene) beads are prepared. All beads exhibit 3D-interconnected microcellular morphology and substantial semiconducting properties, such as strong light harvesting ability in the visible light region with electrochemical band gaps in the range of 2.05-2.33 eV. Finally, the promising photocatalytic activity of these conjugated beads is demonstrated for a model sulfoxidation reaction under visible light irradiation, and near quantitative conversions with excellent chemoselectivities (>99%) are obtained.

The synthesis and characterization of ylideneisoindolinones

1,3-Diiminoisoindoline (DII) and the closely related molecule, iminoisoindolinone are important precursors in the synthesis of macrocycles and chelates such as phthalocyanines, and bis(arylimino)isoindolines, as well as chromophores including aza-BODIPY dyes. A series of seven ylideneisoindolinones are presented in this report. The reaction of various organic CH acids and iminoisoindolinone produce compounds that show strong [Formula: see text]* transitions in the UV region. The chromophores have been characterized spectroscopically and the X-ray structures show electronic delocalization across the chromophore. Additionally, DFT and time-dependent DFT calculations confirm the lower energy absorbances are primarily HOMO-LUMO transitions.

Conjugated Cationic Pp-x Formed on g-C3N4 for Photocatalyzed Water Splitting

Polycationic Pp-x@g-C₃N₄ composite was synthesized through an in situ polymerization process of N-alkylpyridinium acetylenic alcohol bromide (p-x) above the surface of g-C₃N₄. The structure of p-0 and the Pp-x@g-C₃N₄ properties were checked by modern technologies. Photocatalytic tests of Pp-x@g-C₃N₄ in water splitting unveiled much better Pp-x@g-C₃N₄ hydrogen evolution activities by comparison with both g-C₃N₄ and Pp-0. The hydrogen production by Pp-0@g-C₃N₄ was 1654.5 μmol h^-1 g^-1, which is ∼26- and 22-fold greater in relation to what g-C₃N₄ and Pp-0 produced (62.7 and 75.0 μmol h^-1 g^-1, respectively), suggesting strong bilateral and synergistic interactions of g-C₃N₄ with Pp-0. Although the lengthening methylene chain in the polymers weakened the hydrogen generation ability of Pp-x@g-C₃N₄, the conjugated double bonds, solubilization, and dispersion of Pp-x polycationic surfactants made Pp-x@g-C₃N₄ superior to g-C₃N₄ in water splitting. Due to the readily available raw materials, a simple way of preparation (starting chemicals to p-0 to Pp-0@g-C₃N₄), high photocatalysis efficiency, light irritation stability, recyclable ability, and low toxicity, Pp-0@g-C₃N₄ is a good candidate for water splitting.

A New Conducting Polymer with Exceptional Visible-Light Photocatalytic Activity Derived from Barbituric Acid Polycondensation

A novel covalent, metal-free, photocatalytic material is prepared by thermal polymerization of barbituric acid (BA). The structure of the photocatalyst is analyzed by using scanning electron microscopy, X-ray diffraction, and infrared, UV-visible, and ¹ H solution and ¹³ C solid-state NMR spectroscopy. The photodegradation efficiency of BA thermally polymerized at different temperatures is tested by photocatalytic degradation of aquatic rhodamine B (RhB) dye under visible-light irradiation. It is shown that heating BA at an optimized temperature of 300 °C, that is, still in the range that polymer-like polycondensation takes place, results in a photocatalyst that can remove RhB with 96% photodegradation efficiency after 70 min exposure to visible light. The polycondensation reaction of BA is identified to process through precipitation of trimer units as primary building blocks. Reference experiments such as addition of scavengers and saturation with oxygen are studied to understand the photodegradation process. It is shown that the presence of triethanolamine, and excess of oxygen and p-benzoquinone in the solution of RhB and photocatalyst (BA300) is not beneficial, but decreases the photodegradation efficiency.