Di Amine BODIPY and BOPHY as Dual sensor of pH and selective to Cu2+

This work reports the synthesis and characterization of two di-amino-functionalized dyes based on BODIPY and BOPHY, designed as dual optical sensors for pH and metal ions, with particular selectivity toward Cu²⁺. Owing to the presence of amino groups, both compounds exhibit environment-dependent fluorescence modulation, showing a reversible “on–off” fluorescence behavior in response to acidic conditions and metal coordination. Spectroscopic studies reveal that under acidic pH (below 4), both dyes undergo significant changes in absorption and exhibit enhanced fluorescence, attributed to protonation of the amino groups and a reduction in nitrogen pyramidal inversion. Moreover, both compounds display distinct optical responses upon exposure to various metal salts, with BODIPY showing selective and transient fluorescence activation in the presence of copper sulfate under near-neutral conditions. Detailed analyses suggest the formation of three distinct species during the Cu²⁺ interaction: (I) the native dye, (II) a highly fluorescent intermediate complex, and (III) a non-emissive decomposition product. The kinetics and stability of these species were found to be highly dependent on the solvent environment, particularly its protic/aprotic nature. These findings underscore the potential of these small, structurally simple dyes as efficient dual-function sensors, offering broad applicability in environmental monitoring, biological imaging, and chemical sensing.