Photoelectron Spectroscopy of Fulvenallenyl and Fluorine-Substituted Fulvenallenyl Anions

The anion photoelectron spectra of C₇H₅^-, C₇H₄F^- and C₇H₃F₂^- generated in a photoemission anion source with the benzene, fluorobenzene, and p-difluorobenzene precursors, respectively, are presented and analyzed with supporting density functional theory calculations. Patterns in the mass spectra recorded for these three separate precursors suggest that the anions may be formed through C or C^- addition to the benzene or fluorobenzene rings. The spectrum of C₇H₅^- can be definitively assigned to the anion of the fulvenallenyl radical, which is the most stable structural isomer of both C₇H₅^- and ^•C₇H₅. The spectra of C₇H₄F^- and C₇H₃F₂^- are also consistent with fulvenallenyl structures. Assignment to a specific regioisomer of the fluorofulvenallenyl or difluorofulvenallenyl anion is less certain, though we eliminate the possibility of structures featuring a -C≡C-F group. The electron affinities of the radicals trend upward with fluorination, but only modestly, a result of delocalization of the SOMO of the neutral radical (HOMO of the anion) over the entire molecule. Computational results on the electronic and molecular structures of these species are explored.