5-Bromo-4′,5′-bis(dimethylamino)fluorescein: Synthesis and Photophysical Studies

In this study, three new fluorescein derivatives—5-bromo-4′,5′-dinitrofluorescein (BDNF), 5-bromo-4′,5′-diaminofluorescein (BDAF), and 5-bromo-4′,5′-bis(dimethylamino)fluorescein (BBDMAF)—were synthesized and their pH-dependent protolytic equilibria were investigated. In particular, BBDMAF exhibited pH-dependent fluorescence, showing strong emission only at pH 3–6. BBDMAF bears a bromine moiety and thus, can be used in various cross-coupling reactions to prepare derivatives and take advantage of its unique emission properties. To confirm this, the Suzuki and Sonogashira reactions of BBDMAF with phenylboronic acid and phenylacetylene, respectively, were performed, and the desired products were successfully obtained.