Pyridinium betaines derived from thiazolo and imidazoacridinones

Four betaines derived from imidazo[4,5-a], imidazo[5,4-a] and thiazolo[5,4-a]acridine have been prepared in a six step procedure starting from 2-chlorobenzimidazoles and benzothiazoles. The 1H and 13C nmr has been used to characterize the compounds, particularly the orientation of the step leading to the formation of the acridinone ring. The uv-visible spectra of one betaine (wave numbers v in cm−1) shows a linear dependence with Reichardt's ET parameter and a high sensitivity to solvent effects.