Synthetic Approach to Readily Accessible Benzofuran-Fused Borondipyrromethenes as Red-Emitting Laser Dyes

We
took advantage of the chemoselective meso-functionalization
of 2,3,5,6-tetrabromo-8-methylthioBODIPY 6 to prepare
a series of 2,3,5,6-tetrabromo-8-arylBODIPY derivatives suitable for
SNAr substitution reactions with phenols exclusively at
positions 3 and 5. Pd(0)-catalyzed intramolecular arylation reaction
ensued on the remaining brominated positions 2 and 6 to give a new
family of benzofuran-fused BODIPY dyes. This method utilizes readily
available starting materials and allows for the preparation of the
title compounds with excellent functional group tolerance. Moreover,
it was demonstrated that the methodology described herein is amenable
for the incorporation of biomolecules. The photophysical and lasing
properties of the benzofuran-fused BODIPY dyes were thoroughly analyzed
with the aid of electrochemical measurements and quantum mechanical
simulations. These dyes show bright and intriguing emission (both
fluorescence and laser) toward the red edge of the visible spectrum
with remarkable tolerance under strong and continuous irradiation.