Pinpoint-Fluorinated Polycyclic Aromatic Hydrocarbons (F-PAHs): Their Synthesis via Electrophilic Activation of Fluoroalkenes and Properties

On treatment with a cationic Pd (II) catalyst in the presence of BF3 center dot OEt2, 1,1-difluoroalkenes and 1,1,2-trifluoroalkenes underwent Friedel-Crafts-type ring closures (direct activation) to afford pinpoint-monofluorinated and pinpoint-vic-difluorinated phenacenes (F-phenacenes), respectively. Treatment of 1,1-difluoroallenes with an InBr3 catalyst facilitated domino cyclization (indirect activation) leading to the synthesis of F-phenacenes and related F-PAHs. Using the formed F-PAH library, the physical properties of these compounds were investigated. Notably, the HOMO-LUMO energy gaps of F-picenes, consisting of five benzene rings, were smaller than that of the corresponding fluorine-free picene by 0.02-0.26 eV. The HOMO energy levels of F-picenes were lowered by 0.10-0.22 eV, leading to enhanced resistance of these materials to aerial oxidation. 5-Fluoropicene and 13-fluoropicene exhibited p-type semiconducting behavior [5fluoropicene: 2.8 x 10(-5) cm(2)/Vs (vacuum deposition); 13-fluoropicene: 6.6 x 10(-2) cm(2)/Vs (vacuum deposition), 1.3 x 10(-4) cm(2)/Vs (spin casting)]. The introduction of fluorine substituent (s) into picenes increased their solubilities in organic solvents, which was best exemplified by the much higher solubilities of 6-fluoropicene (5.3 wt%), 6,7-difluoropicene (5.3 wt /0), and 13-fluoropicene (3.1 wt%) in THF, compared to that of picene (0.20 wt%).