Tuning the Photophysical Properties and Photostability of Bis(naphthobipyrrolylmethene) derived BODIPY via Functionalization

A series of NIR absorbing and emitting, naphthobipyrrole derived BODIPY dyes are reported. These dyes possess different functional groups viz. -CHO, -CN, -NO2, -Br and Ph at its α,α'-positions. All the derivatives were characterized thoroughly via various spectroscopic means as well as single-crystal X-ray structural analyses. Impacts of functionalization on its photophysical properties as well as photostability were evaluated. For instance, incorporation of the phenyl moieties at the α, α'-positions by Suzuki coupling of the dibromo-derivative 4 with phenyl boronic acid led to substantial bathochromic shift in absorption (762 vs 727 nm) and emission (778 vs 744 nm) relative to the unsubstituted parent dye VI. Theoretical calculations have been performed by ground state optimization to evaluate the electronic transitions which supports experimental observation.