Core-Fluorinated BODIPYs – a New Family of Highly Efficient Luminophores

Abstract

A modular synthesis of novel series of 1,7-difluorinated BODIPYs has been elaborated. First, the acid-catalyzed condensation of ethyl 3-aryl-4-fluoro-1H-pyrrole-2-carboxylates with aromatic aldehydes gives the corresponding dipyrromethane-1,9-dicarboxylates. The latter are subjected to the exhaustive reduction with lithium aluminum hydride to transform the ester moieties into methyl groups. The subsequent oxidation of the resulting 1,9-dimethylated dipyrromethanes followed by the boron difluoride complexation afforded a family of novel core-fluorinated BODIPYs in up to 74 % yield. Photophysical properties of the resulting BODIPYs were tuned by varying of the starting fluoropyrroles and aromatic aldehydes and were studied by UV-visible and fluorescence spectroscopy. As a result, the fluorescence quantum yields of the obtained compounds reached up to 99 %. In addition, their ability to generate singlet oxygen and electrochemical properties were also evaluated. As a result, a new promising family of fluorophores with a good combination of the fluorescence and photosensitizing properties was obtained. It was found that conversion of ester groups into methyl ones at the 3,5-positions of the BODIPY core is a crucial step toward fluorescence enhancement. In addition, DFT calculations were performed to elucidate a relationship between electronic structure, geometry and photophysical properties of these BODIPYs.