Synthesis and spectral properties of long-wavelength fluorescent dyes

Benzo[a]phenoxazinium salts were synthesised by reacting 5-alkylamino-2-nitrosophenol hydrochloride with N-alkylated-naphthylamine in good to excellent yields. Photophysical properties of these fluorophores with emphasis in solvent effects were studied. Remarkable shifts in the absorption and emission maximum have been observed as a function of polarity and proton accepting capability of the solvents. The influence on the fluorescence quantum yield was also studied.