Solution-phase synthesis of Clar’s goblet and elucidation of its spin properties

Abstract

In the traditional view, spin pairing occurs between two electrons in a chemical bond where the bonding interaction compensates for the penalty of electrostatic repulsion. It is a mystery whether spin pairing can occur between two non-bonded electrons within a molecular entity. Unveiling this type of spin entanglement (that is, pairing between two spatially segregated spins) at the molecular scale is a long-standing challenge. Clar’s goblet, proposed by Erich Clar in 1972, provides an ideal platform to verify this unusual property. Here we report the solution-phase synthesis of Clar’s goblet and experimental elucidation of its spin properties. Magnetic studies reveal that the two spins are spatially segregated with an average distance of 8.7 Å and antiferromagnetically coupled in the ground state with an ΔES–T of −0.29 kcal mol−1. Our results provide insight into the spin entanglement in Clar’s goblet and may inspire the design of correlated molecular spins for quantum information technologies. In 1972, Erich Clar envisioned Clar’s goblet, a polycyclic aromatic hydrocarbon featuring two unpaired electrons that are spin-paired. However, synthesizing it in a solution phase remains challenging. Now a derivative of Clar’s goblet has been prepared in solution, and spin entanglement at the molecular scale has been demonstrated experimentally.