Regioselective electrophilic aromatic borylation as a method for synthesising sterically hindered benzothiadiazole fluorophores.

Regioselective stepwise phenylation of 4,7-diarylbenzo[ c ][1,2,5]thiadiazole fluorophores has been achieved through a facile one-pot, three-step synthetic strategy involving sequential borylation, hydroxydechlorination and Suzuki-Miyaura cross-coupling reactions. Crucial to the selectivity was the use of BCl 3 to regioselectively install a boronic acid group in the ortho -position of only one of the diaryl groups. The subsequent introduction of ortho -phenyl groups through Suzuki-Miyaura cross-coupling gave rise to twisted structures with hindered intramolecular rotation, providing a structural lever with which the fluorophore absorption and emission properties could be adjusted.