1,3-thiazolium-4-aminides: syntheses and characterization of fluorescent mesoionic compounds
A series of mesoionic 1,3-thiazolium-4-aminides was synthesized starting from thioamides and chloroacetonitrile via cyanomethylbenzimidothioates which were cyclized by benzoylchloride. Depending on the reaction conditions 4-amino-1,3-thiazolium salts and 4-N-benzamido-1,3-thiazolium salts were obtained (X-ray structure analysis). Substitution of the amino groups with benzoyl chloride gave a series of the title mesoionic compounds (X-ray structure analysis) which were examined spectroscopically. Negative solvatochromism was found and temperature-dependent as well as time-resolved fluorescence measurements were made. Long lifetimes of the excited states (30–50 ns) were detected. Calculated frontier orbital profiles gain insight into the characteristics of 1,3-thiazolium-4-aminides as conjugated mesomeric betaines.