Carboxyl-BODIPY based fluorescent biomarkers: spectral characteristics, photostability and possibilities for practical application

A comparative analysis of the structural and solvation factors on the spectral properties, pH stability, photostability, and lipophilicity of BODIPY luminophores containing carboxylic acid residues in α- and meso-position was carried out. The interaction of these BODIPYs with cells of microscopic fungi (Candida albicans and Fusarium solani) was studied. The compounds were found to be stable across a wide range of pH values and exhibited intense fluorescence (to φ ∼ 94%) at 508–587 nm. The introduction of a carboxylic acid residue into the meso-position of the BODIPY core causes a noticeable increase (almost ∼2 times) of the Stokes shift compared to the meso-unsubstituted analogues. On the other hand, α-carboxyl-BODIPYs showed a red shift in both the absorption and fluorescence bands. Effective fluorescence quenching (up to 40–80%) was observed in electron donor solvents for carboxyl-BODIPYs, especially for the carboxylic acid BODIPY with a thiophene substituent. The presence of a carboxyl group in the α-position of the BODIPY increased its affinity to hydrophilic media by approximately ∼1.2–2 times compared to meso-carboxyl-BODIPYs. Given the lack of cytotoxicity, carboxyl-BODIPYs may be recommended as effective biomarkers for examining the differences between a wide range of pathogens causing mycotic.