Synthesis of π-expanded BODIPYs and their fluorescent properties in the visible–near–infrared region

A series of π-expanded boron–dipyrromethenes (BODIPYs) fused with aromatic rings at β,β-positions, such as benzene, acenaphthylene, and benzofluoranthene were prepared by the reaction of BF3·OEt2 with bicyclo[2.2.2]octadiene-fused dipyrromethene and the subsequent retro Diels–Alder reaction. These BODIPYs exhibited the absorptions and the fluorescence emissions over wide range of visible–near–infrared region at 500–800 nm. BODIPYs composed of two fluorantho[8,9-f]isoindoles absorbed and emitted at red-region over 750 nm with absolute fluorescence quantum yield (Φf) of ca. 0.3, although they are unstable under air in room light. BODIPY composed fluorantho[8,9-f]isoindole and acenaphtho[1,2-c]pyrrole was stable and showed a bright fluorescence emission at 695 nm with high Φf of 0.70.