Efficient synthesis and properties of bis-benzothiophene[b]-fused BODIPY dyes via Pd(PPh3)2Cl2-catalyzed regioselective cyclization

A new method for synthesizing bis-benzothiophene[b]-fused BODIPYs has been developed, enabling the regioselective catalytic cyclization of tetrahalogenated BODIPY, yielding three new near-infrared (NIR) fluorescent dyes, BBTB-1, BBTB-2 and BBTB-3, with high yields (70–77 %) using Pd(PPh₃)₂Cl₂ as a catalyst. This advancement not only enhances synthesis efficiency but also opens new possibilities for designing BODIPY dyes with finely tuned optoelectronic properties. X-ray crystal structure exhibited their excellent planar π-conjugation. Compared to BBTB-3 with electron-donating groups, photophysical and electrochemical analyses of these bis-benzothiophene[b]-fused BODIPYs with electron-withdrawing groups at the meso-position (BBTB-1 and BBTB-2) demonstrated red-shift in both absorption and fluorescence spectra, and a reduction in LUMO energy level and a narrowed HOMO-LUMO gap. Notably, the LUMO energy level of BBTB-1, BBTB-2 were reduced to −3.81 and −3.83 eV, respectively. The exceptional properties of these bis-benzothiophene[b]-fused BODIPYs are expected to broaden their potential application, particularly in organic semiconductor materials, where such optoelectronic characteristics are crucial for enhancing performance.