Synthesis and properties of hexaarylated AzaBODIPYs

Abstract

Sterically crowded 1,2,3,5,6,7-hexaarylated azaBODIPYs were synthesized in 25–35 % yields by coupling 1,3,5,7-tetraaryl azaBODIPYs with six different aryl boronic acids under Pd(0) coupling conditions. The moderate reaction yields were attributed to steric congestion caused by two additional aryl groups introduced at the tetraaryl azaBODIPY core. The compounds were characterized by HRMS, 1D and 2D NMR spectroscopic techniques. The ¹H, ¹⁹F and ¹¹B NMR studies of hexaarylated azaBODIPYs showed slight upfield shifts compared to tetraaryl azaBODIPY indicating the slight alteration of electronic properties of azaBODIPY core upon introduction of two additional aryl groups on tetrararyl azaBODIPY. The absorption and fluorescence bands of hexaarylated azaBODIPYs experienced 7–10 nm hypsochromic shifts compared to tetraaryl azaBODIPY. The hexaarylated azaBODIPYs are weakly fluorescent with significant reduction in quantum yields and singlet state lifetimes compared to tetraarylated azaBODIPY.