Aromatic Ring Fused BOPHYs as Stable Red Fluorescent Dyes

Facile synthetic routes to a new class of red α-benzo-fused BOPHYs with 6,5,6,6,5,6-hexacyclic fused rings and β-thiophene-fused BOPHYs with 5,5,6,6,5,5-hexacyclic fused rings are presented. These dyes were characterized by NMR spectroscopy, HRMS, X-ray structure analysis, cyclic voltammetry, and optical measurements. Compared to parent BOPHY, significant red-shifts in the absorption (up to 600 nm in solution) and emission (up to 648 nm in solution and 717 nm in solid state), as well as high chemical stability and photostability, were found for these aromatic-ring-fused BOPHY dyes. As shown in cyclic voltammetry and DFT calculations, the aromatic ring fusions induced significantly increased HOMO energy levels, giving effective expansion of π-conjugation over these BOPHY dyes. These new molecular skeletons would be promising candidates for various applications in light of their unique structure and attractive photophysical properties.