Synthesis and properties of B-cyano-BODIPYs

A series of boron-functionalized BODIPY dyes with cyano groups were prepared from their corresponding BF2 derivatives using SnCl4/TMSCN at room temperature for 10 min. Replacement of the fluorines by cyano groups reduces the B–N bond lengths, decreases the charge on boron, and causes characteristic 11B NMR chemical shifts. The 4,4′-dicyano-BODIPYs show significantly enhanced stability to acidic conditions (excess TFA) and, with one exception, enhanced fluorescence quantum yields. Furthermore, the B(CN)2-BODIPYs were non-cytotoxic to HEp2 cells, both in the dark and upon exposure to light (1.5 J/cm2), and rapidly accumulated within cells, localizing mainly in the lysosomes, ER and Golgi.