Dynamic redox systems based on bis(spiroxanthene)-type donors with a polycyclic aromatic hydrocarbon: preparation, X-ray structures, and electrochromic response with fluorescence change

The long C–C bonds (1.614(2)–1.630(2) Å) in newly prepared title donors 2–6 are cleaved upon two-electron oxidation to afford the bond-dissociated dicationic dyes 22+–62+, whose electron affinities are stronger than the corresponding biphenyl-2,2′-diyl dications 12+ due to the spatial proximity of two xanthenylium units. Not only UV–vis but also fluorescence spectra changed drastically upon electrolysis since only colorless neutral donors are fluorescent.