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.