Substituent Effects at the 5-Position of 3-[bis(pyridine-2-ylmethyl)amino]-BODIPY Cation Sensor Used for Ratiometric Quantification of Cu²⁺

Abstract

In this paper, we investigated the effects of substitution at the 5-position of an asymmetric BODIPY cation sensor to tune its spectroscopic, photophysical, and cation-sensing properties. We introduced substituent groups with differing electron density at the 5-position of 3-[bis(pyridine-2-ylmethyl)amino]-BODIPY, which contains a cation recognition moiety at the 3-position of the BODIPY core, to develop four sensors which all exhibited distinctive ratiometric spectral changes in the presence of Cu²⁺. Aromatic substitution increased the Stokes shift. Substitution with the electron-withdrawing sulfonylphenyl group resulted in the highest fluorescence quantum yield, largest absorption coefficient, and largest spectral shift in the presence of Cu²⁺. The sulfonylphenyl-substituted sensor also exhibited excellent selectivity for Cu²⁺.