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Three boron-dipyrrine (BODIPY) based dyes with bulky substituents in 8-position of dipyrrin ligand have been synthesized and characterized. Photophysical properties of the obtained compounds have been investigated in different individual solvents and solvent mixtures. Investigated compounds was found to be intensive fluorescent molecular rotors. The influence of different solvent parameters and the substituent nature on rotor characteristics have been observed and discussed. Minor changes in the nature of 8-substituent does not influence the spectral properties, but the presence of nitrogen donor atom in the phenyl substituent could be used for the sensing of the donor-acceptor interactions with solvent or dissolved compounds. The new approach of spectral properties correlation with solvent parameters was proposed, the viscosity parameter should be taken into account in case of BODIPYs with bulky substituents. The intensity of fluorescence molecular rotor properties decrease gradually with the viscosity increase above 1 cP.

Two boron-dipyrrin (BODIPY) based dyes with dimethylaminophenyl and carboxyphenyl substituents in 8-position of dipyrrin ligand have been synthesized and characterized. Photophysical and spectral properties of the obtained compounds have been investigated in water-ethanol mixture and water-cyclohexane system with variation of pH values. The equilibria constants of the compounds were identified by classical methods of acid-base titration. BODIPY bearing dimethylaminophenyl and carboxyphenyl subunits show deprotonation/protonation dependent fluorescence off/on-switching. The change of the emission could be mechanistically explained by a PET (photoinduced electron transfer) from the 8-substituent to the fluorophore. The present study demonstrates that BODIPY-based fluorescent sensors can be used to measure the pH in the range of 2-13 extending the scope of BODIPY dyes available as pH-indicators. Investigated compounds demonstrate weak dye-dye interaction allowing their cooperative usage as indicators.

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