Asymmetric and Symmetric S-<i>zig-zag</i>-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-<i>zig-zag</i>-fused BODIPYs (<b>s-TFB</b> and <b>bis-TFB</b>) 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 <i>zig-zag</i> edge of the BODIPY core results in blue-shifted absorption and emission spectra, with <b>bis-TFB</b> exhibiting maxima at 530 and 539 nm and elevated LUMO energy levels. In contrast, oxidation of <b>s-TFB</b> and <b>bis-TFB</b> with <i>m</i>-CPBA demonstrates significant site selectivity, affording four oxidation products, namely <b>s-s-SFB</b>, <b>s-bis-SFB</b>, <b>bis-s-SFB</b>, and <b>bis-bis-SFB</b>, in yields ranging from 22% to 36%. These oxidated S-<i>zig-zag</i>-fused BODIPY derivatives display large red-shifted absorption and emission spectra (e.g., 648 and 735 nm for <b>s-bis-SFB</b>), along with more stable HOMO and LUMO energy levels and reduced HOMO-LUMO gaps. This S-<i>zig-zag</i>-fused cyclization/oxidation strategy enables precise tuning of the BODIPY optoelectronic properties, opening new avenues in dye design and application.