Evidence of a Photoinduced Electron-Transfer Mechanism in the Fluorescence Self-quenching of 2,5-Substituted Selenophenes Prepared through In Situ Reduction of Elemental Selenium in Superbasic Media

Abstract

A series of new 2,5-disubstituted selenophene derivatives are described from elemental selenium and 1,3-diynes in superbasic media. The activation of elemental selenium in a KOH/DMSO system allows cyclization with conjugated diynes at room temperature. The cyclization reaction is extended to a broad range of functional groups, for which photophysics were experimentally and theoretically investigated. The selenophene derivatives present absorption maxima in the UV-A region and fluorescence emission in the violet-toblue region. Fluorescence decay profiles were obtained showing a monoexponential decay with fast fluorescence lifetimes (∼0.118 ns), as predicted by the Strickler−Berg relations. In general, in both investigations, no dependence on the solvent polarity on the absorption and emission maxima location was observed. On the other hand, solvents and substituents are shown to play a role in the fluorescence quantum yield values. In addition, a fluorescence selfquenching behavior could be observed, related to a photoinduced electron-transfer mechanism. Theoretical calculations performed at the MP2/ADC(2)/cc-pVDZ level of theory were performed in order to investigate the photophysical features of this series of selenophene derivatives.

Palladium-Catalyzed Direct Selanylation of Chalcogenophenes and Arenes Assisted by 2-(Methylthio)amide

“…The roles of organoselenides are well established in organic synthesis, and many of these critical synthetic intermediates have a prominent position in the construction of complex molecules . Likewise, these organic frameworks have been successfully applied as functional organic materials due to the remarkable effects on their physical and electronic properties provided by the introduced selenium atom in π-extended systems . Therefore, there is a great demand from the pharmaceutical and optoelectronic device industries for the development of straightforward methods for C–Se bond formation to meet the practical requirements …”

“…The guided regiocontrol by directing groups in transition metal-catalyzed transformations is a well-known strategy successfully applied to direct selanylation of arenes . However, this approach was sidelined for the C3 selective direct chalcogenylation of chalcogenophenes despite their great relevance as building blocks for organic functional materials and drug discovery. , …”

Synthesis of 2,5-disubstituted selenophenes via a copper-catalyzed regioselective [2+2+1] cyclization of terminal alkynes and selenium

“…Simultaneously, the dropped hydrogens from 1a are captured by the selenide anion in the reaction system and a H 2 Se species is generated. Next, the hydroselenation of the alkyne moiety occurs in the presence of the Cu( i ) catalyst and H 2 Se, 19,20 which affords the intermediate A . Then, A is tautomerized to intermediate B 21 and soon re-coordinates with the Cu( i ) catalyst, which further converts to the selenonium ion C through an intramolecular nucleophilic attack of selenium.…”

“…Simultaneously, the dropped hydrogens from 1a are captured by the selenide anion in the reaction system and a H 2 Se species is generated. Next, the hydroselenation of the alkyne moiety occurs in the presence of the Cu(I) catalyst and H 2 Se, 19,20…”