Di amine BODIPY and BOPHY as dual sensor of pH and selective to Cu2+

Abstract

This work reports the synthesis and characterization of two diamino functionalized dyes based on BODIPY and BOPHY, designed as dual optical sensors for pH and metal ions, especially Cu²⁺. Both compounds display environmentally modulated fluorescence, with reversible “on-off” behavior upon changes in pH and metal coordination.

Spectroscopic studies reveal that, in acidic media (pH ≤ 4), both dyes experience a notable increase in fluorescence (up to 25 or 250-times for BODIPY and BOPHY, respectively), along with color changes clearly visible to the naked eye. These effects are accompanied by hypsochromic shifts in the absorption bands, on the order of 30–80 nm, which are attributed to the protonation of the amino groups and the reduction of the pyramidal inversion of nitrogen. 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.