α‐/β‐Formylated Boron–Dipyrrin (BODIPY) Dyes: Regioselective Syntheses and Photophysical Properties

Formylation has been performed on pyrrole‐unsubstituted dipyrromethanes 1 and boron–dipyrrin (BODIPY) dyes 4 based on a Vilsmeier–Haack reaction. It is highly regioselective and complementary and occurs exclusively at the α‐ and β‐position, respectively, for pyrrole‐unsubstituted dipyrromethanes 1 and BODIPY dyes 4. This regioselective formylation enables the syntheses of a variety of α‐ and β‐substituted BODIPY dyes. The installation of formyl groups affects the electronic properties of the BODIPY chromophore, resulting in red‐ and blueshifts of the absorption and emission maxima, respectively, for the α‐ and β‐formylatedBODIPYs 3 and 5.