An Open-Shell Coronoid with Hybrid Chichibabin-Schlenk Conjugation

A hexaradicaloid molecule with alternating Kekulé and non-Kekulé connectivities between adjacent spin centers was obtained by fusing two conjugation motifs in Chichibabin and Schlenk hydrocarbons into a coronoid structure. ¹ H NMR, ESR, and SQUID experiments and computational analyses show that the system has a singlet ground state with a significant hexaradicaloid character (γ₀ =0.826, γ₁ =γ₂ =0.773). It has multiple thermally accessible high-spin states (up to the septet), with uniform energy gaps of ca 1.0 kcal mol^-1 between consecutive multiplicities. In line with its open-shell character, the coronoid has a small electronic band gap (ca. 0.8 eV) and undergoes two consecutive one-electron oxidations at low potentials, yielding cationic forms with extended near-infrared absorption. The hexaradicaloid, which combines open-shell and macrocyclic contributions to its π conjugation, is an example of a design strategy for multistate spin switches and redox-amphoteric NIR dyes.