Synthesis and Optical Properties of Unsymmetric Aromatically π-Extended BODIPY.

A series of unsymmetrically substituted BODIPY dyes featuring fused benzo- or naphtho-fragments on one pyrrolic unit were synthesized from the corresponding pyrrolic precursors. The synthetic route was optimized using a modular approach based on the condensation of formylpyrroles with alkylpyrroles, enabling the identification of precursor combinations that minimize byproduct formation and improve preparative yields. The resulting benzo- and naphtho-fused BODIPYs display intense fluorescence in the red region, with emission maxima spanning 590-680 nm and fluorescence quantum yields ranging from 0.27 to 0.84. Their two-photon absorption (2PA) properties were studied both experimentally and computationally. An increase in the two-photon absorption cross-section with an increase in the size of the π-conjugated system was observed, reaching 80 GM for the naphthoBODIPY derivative. These findings demonstrate the potential of π-extended BODIPY scaffolds as NIR-active fluorophores with enhanced nonlinear optical properties.