Journal Article

Open‐Shell States in Dynamic Diradicaloids

Pawlicki, Miłosz, Dzieszkowski, Krzysztof

2025

Overview

The open‐shell organic and carbon‐based systems, with either a doublet, triplet or higher spin‐states, play a key role in contemporary research, opening potential applicability for several crucial fields. Among those derivatives, specific attention has been given to p‐phenylene‐based systems derived from the original Thiele hydrocarbon. These systems stabilize an open‐shell diradicaloid resonance structure with a thermally accessible triplet state and are derived from a quinone‐benzene (Clar's sextet) equilibrium. In our discussion, we very carefully choose examples which focus on fundamental derivatives that merge diatropic subunits, ready to stabilize two unpaired electrons via a dynamic modulation of geometry. This process provides an additional factor to the resonance energy of aromatics, mostly responsible for stabilization of two unpaired electrons. This Perspective analyses geometric factors crucial for stabilization of the open‐shell states in dynamic diradical(oid)/biradical systems derived from a quinone‐benzene resonance and entrapped in the p‐phenylene Kekulé structure forms. It correlates them with the resonance energy, allowing stabilization of open‐shell singlet/triplet states solely by changing the dihedral angle (δ or/and θ) that homolytically breaks the π‐bond, introducing Clars sextet(s).

• Subject: Chichibabin hydrocarbon / Diradicals / Dynamic hydrocarbons / Phenylenes / Stable radicals