Pulling with the Pentafluorosulfanyl Acceptor in Push-Pull Dyes.

A new class of push-pull fluorophores featuring the pentafluorosulfanyl (SF5) group as a potent acceptor has been synthesized. Known for its excellent chemical and thermal stability, the unique SF5 functionality is also strongly electron-withdrawing but at the same time highly lipophilic. We report six new fluorescent dyes, which were characterized by UV-vis/fluorescence spectroscopy, single-crystal X-ray diffraction, and cyclic voltammetry. Notable dye properties include large Stokes shifts (>100 nm), pronounced solvatofluorochromic effects arising from intramolecular charge transfer, moderate fluorescence quantum yields in both solutions and thin films, and extensive supramolecular C-H···F interactions in their crystalline states. Reversible mechanofluorochromism was also observed in dye 5, where grinding and fuming of a solid sample gave blue- and red-shifted emissions, respectively. Postfunctionalization of dye 3 to afford a pair of strong visible-light absorbers was also demonstrated.