Bistability between π-diradical open-shell and closed-shell states in indeno[1,2-a]fluorene

Indenofluorenes are non-benzenoid conjugated hydrocarbons that have received great interest owing to their unusual electronic structure and potential applications in nonlinear optics and photovoltaics. Here we report the generation of unsubstituted indeno[1,2- a ]fluorene on various surfaces by the cleavage of two C–H bonds in 7,12-dihydroindeno[1,2- a ]fluorene through voltage pulses applied by the tip of a combined scanning tunnelling microscope and atomic force microscope. On bilayer NaCl on Au(111), indeno[1,2- a ]fluorene is in the neutral charge state, but it exhibits charge bistability between neutral and anionic states on the lower-workfunction surfaces of bilayer NaCl on Ag(111) and Cu(111). In the neutral state, indeno[1,2- a ]fluorene exhibits one of two ground states: an open-shell π -diradical state, predicted to be a triplet by density functional and multireference many-body perturbation theory calculations, or a closed-shell state with a para -quinodimethane moiety in the as -indacene core. We observe switching between open- and closed-shell states of a single molecule by changing its adsorption site on NaCl.