Asymmetric and Symmetric S-zig-zag-Fused BODIPYs: Synthesis and Photophysical and Oxidative Properties

We present a new, straightforward, and versatile approach that utilizes regioselective brominated precursors to synthesize both asymmetric and symmetric S-zig-zag-fused BODIPYs (s-TFB and bis-TFB) in moderate yields (45% and 40%, respectively). X-ray structure analyses reveal that the planar rigidity of the BODIPY skeleton is progressively enhanced with an increasing number of thiopyran rings. The annulation of S-heteroaromatic rings at the zig-zag edge of the BODIPY core results in blue-shifted absorption and emission spectra, with bis-TFB exhibiting maxima at 530 and 539 nm and elevated LUMO energy levels. In contrast, oxidation of s-TFB and bis-TFB with m-CPBA demonstrates significant site selectivity, affording four oxidation products, namely s-s-SFB, s-bis-SFB, bis-s-SFB, and bis-bis-SFB, in yields ranging from 22% to 36%. These oxidated S-zig-zag-fused BODIPY derivatives display large red-shifted absorption and emission spectra (e.g., 648 and 735 nm for s-bis-SFB), along with more stable HOMO and LUMO energy levels and reduced HOMO-LUMO gaps. This S-zig-zag-fused cyclization/oxidation strategy enables precise tuning of the BODIPY optoelectronic properties, opening new avenues in dye design and application.