Charge Separation in Triafulvenes: Application of the Para‐Fluorophenyl Tag ¹⁹f NMR Method

Triafulvene (1) is the simplest [n]fulvene. Interest in triafulvenes centered on the potential contributions (in the ground state) of dipolar ‘aromatic’ structures of the type la, in which three‐membered ring assumes ‘cyclopropenium’ character^2‐5). Various attempts have been made to increase these dipolar contributions by introducing electron withdrawing substituents at the exocyclic carbon atom (C₄) of the triafulvene skeleton^2‐6). A striking illustration of this trend is the study of the triapentafulvalene (2) system, motivated by the search for aromatic ‘cyclopropenium‐cyclopentadienide’ structures (2a)³⁾. Cyclopropenone (3), the simplest [n]annulenone, may also fall within the category of triafulvenes formally being viewed upon as 4‐oxatriafulvene with a potential contribution of a cyclopropenium oxide (3a) structure to the ground state resonance hybride^5,7,8).