Photoinduced intramolecular charge separation (CS) in a polar polymer glass, cyanoethylated pullulan (CN-PUL), was studied below the glass transition temperature (Tg=395 K). A series of three carbazole (Cz: donor)-cyclohexane (S: spacer)-acceptor (A: acceptor) molecules (Cz-S-A) was used as intramolecular donor-acceptor dyads. The photoinduced CS rate was evaluated by the fluorescence decay measurement at temperatures from 100 to 400 K. The CS rate (kCS) increased above 200 K even far below Tg where micro-Brownian motions of the whole polymer chain are frozen. Below 200 K, on the other hand, kCS showed weak dependence on temperature. The temperature dependence of kCS is discussed in terms of the dielectric relaxation time of the polymer matrix. Consequently, CS below Tg was well explained by a thermally nonequilibrium electron transfer (ET) formula above 200 K and by a two-mode quantum-mechanical ET formula below 200 K. The increase in kCS above 200 K is mainly caused by a thermally activated low-frequency matrix mode originating from the side-chain relaxation of polar cyano groups. The weak temperature dependence of kCS can be explained by a nuclear-tunneling effect caused by a high-frequency matrix mode (variant Planck's over 2piomegH=250 cm-1) and an intramolecular vibrational mode (variant Planck's over 2piomegaQ=1300 cm-1). The high-frequency mode of the polymer matrix was attributed to a vibrational or librational motion of polar groups in the CN-PUL glassy solid.
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December 2024
Department of Chemistry, Indian Institute of Technology, Kharagpur, West Bengal, 721302, India.
Anticipating intramolecular excited-state proton-coupled electron transfer (PCET) process within dinuclear Ir-photocatalytic system via the covalent linkage is seminal, yet challenging. Indeed, the development of various dinuclear complexes is also promising for studying integral photophysics and facilitating applications in catalysis or biology. Herein, this study reports dinuclear [Ir(bis{imidazo-phenanthrolin-2-yl}-hydroquinone)(ppy)] (1) complex by leveraging both ligand-centered redox property and intramolecular H-bonding for exploring dual excited-state proton-transfer assisted PCET process.
View Article and Find Full Text PDFChem Commun (Camb)
December 2024
School of Petrochemical Engineering, Changzhou University, Changzhou 213164, P. R. China.
A photocatalytic sulfamoylation/5- cyclization of ()-'-arylidene--phenylmethacrylohydrazides with sulfamoyl chlorides was developed. The chemoselective intramolecular addition of the carbon-centered radical intermediate to the CN bond in the hydrazone motif gave the sulfamoylated pyrazolin-5-one. Besides, sulfonyl chlorides are also suitable reaction partners to access sulfonylated pyrazolin-5-ones.
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December 2024
Key Laboratory of Green Chemistry and Technology of Ministry of Education, College of Chemistry, Sichuan University, 29 Wangjiang Road, Chengdu, 610064, P. R. China.
Trifluoromethylarenes (ArCF) are crucial bioisosteres in medicinal chemistry, but catalyst-free and controlled photo-activation of the ArC(sp)-F bond remains a significant challenge. The photo-induced defluorination acyl fluoride exchange (photo-DAFEx) of m-trifluoromethylaniline, induced by ultraviolet light, emerges as a promising novel photo-click reaction for photoaffinity drug discovery. However, the photophysical properties of NMePhFC(sp)-F derivatives and factors affecting ArC(sp)-F bond activation in photo-DAFEx are not yet fully understood, hindering the development of new photo-defluorination reagents with longer absorption wavelength for the photo-DAFEx.
View Article and Find Full Text PDFProc Natl Acad Sci U S A
December 2024
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
Crit Rev Anal Chem
November 2024
Public Health School, Mudanjiang Medical University, Mudanjiang, China.
Fluorescent sensors reflect information such as the concentration or content of the analysis by interacting with a specific recognition group to change the signal of the fluorophore. It has attracted much attention because of its advantages of high sensitivity, fast detection speed and low cost, and it has become an effective alternative to traditional detection methods. Graphitic phase carbon nitride nanosheets (g-CNNs) are a class of carbon-based fluorescent nanomaterials derived from bulk graphite phase carbon nitride (g-CN), which have attracted much attention from scholars because of their advantages of low cost, simple fabrication, high quantum yield, strong stability and nontoxicity.
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