2,3-Naphtho-Fused BODIPYs as Near-Infrared Absorbing Dyes

2,3-Naphtho-fused boron-dipyrromethenes (BODIPYs) 1a and 1b, which absorb near-infrared light at 740–770 nm with molar extinction coefficients above 105 M–1 cm–1 in THF, have been synthesized through a palladium­(II)-catalyzed direct acylation of N-BOC hydrazones and subsequent Paal–Knorr pyrrole synthesis. Simple benzo-annulation of dibenzo-BODIPY caused a significant red-shift in the absorption. Subsequent intramolecular B,O-cyclization of 1b gave 2, which exhibited an intense absorption band at 830 nm. The structure–optical property relationship has been investigated using theoretical calculations and cyclic voltammetry.