Effect of meso-substituent and solvent nature on spectral properties, pH-stability and affinity to blood transport proteins of BODIPY dyes

The paper is focused on a comparative analysis of the structural and solvation factors on the spectral properties, pH-stability and lipophilicity of BODIPY biomarkers containing in meso-position methyl group, carboxylic acid residues and their esters. The affinity of meso-BODIPYs to blood transport proteins was studied. Dyes intensely absorb (ε ∼ 45000–90000) and fluoresce (to φ ∼ 100 %) in the range of 493–504 and 508–520 nm, respectively. meso-substitution causes a hypsochromic shift (by ∼4–11 nm) of the maximum of the intense absorption band and a noticeable increase of the Stokes shift (up to ∼1.7–2.6 times) of BODIPYs compared to the meso-unsubstituted analog. It has been shown that the introduction of a carboxyl group into the BODIPY meso-position significantly (by a factor of ∼2) increases the hydrophilicity of the compounds, and the presence of ester groups in the structure leads to an increase of the hydrophobicity of the luminophores by a factor of ∼1.3 compared to the meso-unsubstituted dye. It has been demonstrated that compounds are stable in a wide pH range and exhibit intense fluorescence (to φ ∼ 80 %), while carboxyl BODIPYs can be considered as pH sensors for alkaline media. Introducing carboxylic acid residues and their esters into the meso-position of BODIPY is an excellent way to increase affinity dyes to biostructures, including blood transport proteins.