Dyes derived from benzo[ a ]phenoxazine – synthesis, spectroscopic properties, and potential application as sensors for l ‐cysteine

Abstract

Several benzo[a]phenoxazine dyes containing a maleimide moiety have been synthesised and characterised by proton nuclear magnetic resonance spectroscopy and mass spectrometry. The spectroscopic properties, such as absorption and emission spectra, of these dyes – 9-maleimido-5H-benzo[a]phenoxazin-5-one (7a), 6-chloro-9-maleimido-5H-benzo[a]phenoxazin-5-one (7b), and 6-bromo-9-maleimido-5H-benzo[a]phenoxazin-5-one (7c) – were examined. These compounds were evaluated as potential fluorescent and colorimetric probes for the detection of biothiols. Results show that the studied compounds exhibit colorimetric and fluorescent responses to l-cysteine at pH 7.4. In the presence of l-cysteine, the fluorescence intensity of synthesised dyes is greatly enhanced. The addition of l-cysteine to solutions of dyes 7a to 7c also results in red shifts of their absorption bands. The cytotoxic effect of tested dyes 7a to 7c against human neuroblastoma cells (SH-SY5Y) was determined by MTT assay. The fluorescent response of these compounds to thiols SH-SY5Y was examined. The results show that the tested compounds exhibit fluorescent response in this cell line, and the benzo[a]phenoxazine dyes substituted in the 6-position with a halogen (7b and 7c) are less toxic against cells under experimental conditions than their unsubstituted analogue (7a).