Kirara Yamaguchi

Reaction of selenoamide dianions with thio- and selenoformamides leading to the formation of 5-aminoselenazoles: photophysical and electrochemical properties.

5-Amino-2-selenazolines were synthesized by reacting selenoamide dianions generated from secondary selenoamides and BuLi with tertiary thio- and selenoformamides followed by treatment with iodine. The resulting 5-amino-2-selenazolines were further oxidized with iodine to give 5-aminoselenazoles in moderate to good yields. The general tendencies in the (77)Se NMR spectra of the starting selenoamides, 5-amino-2-selenazolines, and 5-aminoselenazoles were determined. The chemical shifts of these compounds were highly influenced by the skeletons involving the selenium atom as well as the substituents on the carbon atoms of each skeleton. The molecular structures of 5-aminoselenazoles were clarified by X-ray analyses, and their electronic structures were elucidated by DFT calculations. Finally, UV-vis and fluorescence spectroscopy and cyclic voltammetry (CV) of 5-aminoselenazoles were performed, and their properties are discussed in relation to the substituents on the selenazole rings.

5-N-Arylaminothiazoles as Highly Twisted Fluorescent Monocyclic Heterocycles: Synthesis and Characterization.

A series of 5-N-arylaminothiazoles was prepared by reacting thioamide dianions derived from secondary thioamides with thioformamides, followed by sequential oxidation with iodine. X-ray analyses demonstrated that they adopt structures that are highly twisted from planar conformations. Their orientations were tuned by the steric and/or electronic interactions of the substituents at their 2-, 4-, and 5-positions. The 5-aminothiazoles exhibited a range of fluorescent emissions, from blue to orange. Although the absorption spectra were independent of the polarity of the solvent, fluorescent emissions were influenced by the polarity of the solvent: in more polar solvents, the emissions were red-shifted. These phenomena were examined in terms of Lippert-Mataga plots and the change in the dipole moment between the ground and excited states. They also exhibited emissions in the solid state, again from blue to orange. Cyclic voltammetry of the 5-aminothiazoles showed reversible waves of one-electron oxidation. The half-potential of the oxidation was reduced by the introduction of electron-donating groups to the phenyl groups on the nitrogen atom at the 5-position. DFT calculations were carried out to determine the energy levels of the HOMO and LUMO. Finally, the results of TG-DTA showed that they are thermally stable.

Pyridinium 5-aminothiazoles: specific photophysical properties and vapochromism in halogenated solvents

Treatment of pyridyl-5-aminothiazoles (1–4) with alkyl triflates or benzyl iodide afforded the corresponding pyridinium 5-aminothiazoles (5–10), which exhibited bathochromically shifted absorption and fluorescence spectra relative to those of 1–4. Moreover, the vapochromic properties of 5 specific to halogenated solvents were examined by powder X-ray diffraction analysis. Pmma films containing 5 can thus be used to detect halogenated solvents, especially CH2Cl2.

CCDC 1540911: Experimental Crystal Structure Determination

Related Article: Toshiaki Murai, Akihito Yoshida, Tomohiko Mizutani, Hiroaki Kubuki, Kirara Yamaguchi, Toshifumi Maruyama, Fumitoshi Shibahara|2017|Chem.Lett.|46|1017|doi:10.1246/cl.170341

Experimental and Theoretical Examination of the Radical Cations Obtained from the Chemical and Electrochemical Oxidation of 5-Aminothiazoles

Abstract Chemical or electrochemical one‐electron oxidation of 5‐N‐arylaminothiazoles was found to afford stable radical cations. For chemical oxidation, 1 equivalent of [(4‐BrC6H4)3N][SbCl6] (Magic Blue, MB) was added to CH2Cl2 solutions of the thiazoles, and the thus‐obtained radicals showed light absorption in the near‐infrared region. Electrochemical oxidation also led to bathochromic shifts in the absorption bands, and the obtained spectra were similar to those derived from the chemically oxidized species. These radicals afforded electron paramagnetic resonance (EPR) spectra that are consistent with the notion of stable nitrogen radicals (half‐life≤385 h). The EPR spectrum of a thiazole containing 4‐dimethylaminophenyl groups on the nitrogen atom at the 5‐position changed significantly upon adding >3 equivalents of MB. Details of the electronic structures of the experimentally obtained radical cations were generated from theoretical calculations.