Synthesis and Characterization of Acetylene‐Linked Bisphenalenyl and Metallic‐Like Behavior in Its Charge‐Transfer Complex

We prepared and isolated a phenalenyl‐based neutral hydrocarbon ( 1 b ) with a biradical index of 14 %, as well as its charge‐transfer (CT) complex 1 b –F 4 ‐TCNQ. The crystal structure and the small HOMO–LUMO gap assessed by electrochemical and optical methods support the singlet‐biradical contribution to the ground state of the neutral 1 b . This biradical character suggests that 1 b has the electronic structure of phenalenyl radicals coupled weakly through an acetylene linker, that is, some independence of the two phenalenyl moieties. The monocationic species 1 b . + was obtained by reaction with the organic electron acceptor F 4 ‐TCNQ. The cationic species has a small disproportionation energy Δ E for the reaction 2× 1 b . + ⇌ 1 b + 1 b 2+ , which presumably originates from the independence of the phenalenyl moieties. The small Δ E led to a small on‐site Coulombic repulsion U eff =0.61 eV in the CT complex. Moreover, a very effective orbital overlap of the phenalenyl rings between molecules afforded a relatively large transfer integral t =0.09 eV. The small U eff /4 t ratio (=1.7) resulted in a metallic‐like conductive behavior at around room temperature. Below 280 K, the CT complex showed a transition into a semiconductive state as a result of bond formation between phenalenyl and F 4 ‐TCNQ carbon atoms.