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

A series of monoreactive functional benzoa]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.