Dihydrobenzofuro[3,2-b]benzofuran: a light-driven molecular switch with fluorescence switching, bistability, and...

Designing photochromic materials with thermally stable bistability, fluorescence switching, and structural responsiveness remains a key challenge in responsive materials. In this study, we introduce photochromic behavior in 4b,9b-dihydrobenzofuro[3,2-b]benzofuran derivatives (DHBs). Guided by bond dissociation energies, we demonstrate that DHB derivatives undergo a reversible, light-induced regioselective ring-opening reaction accompanied by significant changes in structural, electronic, and photophysical properties. Upon UV illumination at 285 nm, the non-conjugated, weakly emissive closed-ring DHB undergoes a regioselective ring-opening to yield a conjugated, hydroxy-functionalized isomer that exhibits strong fluorescence. The reverse ring-closure occurs under 325 nm light, with no observable thermal back reaction, establishing a thermally stable, bistable molecular switch. The rigid, fused structure of DHB possesses intrinsic chirality, as confirmed by single-crystal X-ray diffraction revealing racemic twin crystals with nearly equal enantiopure domains. Enantiomeric separation by chiral HPLC enables the study of its stereochemical and chiroptical properties. Spectroscopic analyses, in both solution and thin films, together with DFT calculations, elucidate photoinduced fluorescence switching behavior, distinct HOMO-LUMO energy levels, and structural transformations between the two isomers. Notably, asymmetric substitution directs the site of bond cleavage, providing a handle to control photochemical reaction pathways. These results highlight the potential of DHB derivatives as a multifunctional photochromic scaffold and open new opportunities for the design of responsive materials with tunable optical and electronic properties.