Synthesis and solvatochromism of 2-(N-pyridinio)-pyrimidin-4-olate and related betaines derived from uracils

Fluorescent betaines: 2-(N-pyridinio)- (1a-c), 2-(3-methyl-N-imidazolio)- ( 2) and 2-(4-dimethylamino-N-pyridinio)-pyrimidin-4-olate (3) were synthesiz ed from uracils. The compounds were subjected to absorption, steady-state a nd time-dependent emission studies. Substituent and solvent effects on the location of the absorption and fluorescence bands were investigated. The ex cited state dipole moment of 2-(N-pyridinio)- and 2-(3-methyl-N-imidazolio) pyrimidin-4-olate was determined from solvatochromic shift of the lowest en ergy absorption band. The fluorescence quantum yields and lifetimes of beta ines in aqueous solution as well as in several organic solvents were measur ed.