title: Excited-state switching by per-fluorination of para-oligophenylenes.
abstract: Fluorination has become a versatile route to tune the electronic and optical properties of organic conjugated materials. Herein we report a new phenomenon, excited-state switching by per-fluorination of para-oligophenylenes, placing a low intensity 1(1)B(2) state below the 1(1)B(1) state, giving rise to large Stokes shifts. The switching is attributed to the specific impact of fluorine on the delocalized and localized frontier orbitals as elucidated by quantum-chemical calculations. The sterical demands of the fluorine atom additionally diminish efficient conjugation along the chain, leading to hypsochromic shifts with respect to the unsubstituted counterparts and to a weak chain length dependence of the absorption and unstructured emission spectra and enhanced internal conversion.
authors.affiliation: Madrid Institute for Advanced Studies, IMDEA Nanoscience, UAM, Modulo C-IX, Av. Tomás y Valiente 7, Campus de Cantoblanco, E-28049 Madrid, Spain.
authors.forename: Begoña
authors.initials: B
authors.lastname: Milián-Medina
authors.forename: Shinto
authors.initials: S
authors.lastname: Varghese
authors.forename: Roberta
authors.initials: R
authors.lastname: Ragni
authors.forename: Herbert
authors.initials: H
authors.lastname: Boerner
authors.forename: Enrique
authors.initials: E
authors.lastname: Ortí
authors.forename: Gianluca M
authors.initials: GM
authors.lastname: Farinola
authors.forename: Johannes
authors.initials: J
authors.lastname: Gierschner
mesh_terms: D005449:Fluorenes / Q000138:chemical synthesis / Q000737:chemistry*; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D015394:Molecular Structure; D011789:Quantum Theory
chemical_list: D005449:Fluorenes; D006841:Hydrocarbons, Aromatic