Functionalised benzo[a]phenoxazine dyes as long-wavelength fluorescent probes for amino acids

A series of monoreactive functional benzo[a]phenoxazinium chlorides with a carboxyl, hydroxyl, amine or chloromethyl group were used as labels in the preparation of long-wavelength fluorescent amino acid bioconjugates. UV–visible and fluorescence studies of all compounds were carried out in ethanol and water at physiological pH. The absorption and emission of all compounds synthesised were in the range 555–640 nm and 632–681 nm, respectively.