# Ion‐Pairing‐Modulated Diradical Properties in Partially Conjugated Negatively Charged π‐Electronic Systems

## TL;DR

Researchers synthesized a complex molecule whose diradical properties can be modulated by ion pairing and structural features.

## Contribution

A new method to modulate diradical properties through ion-pairing and structural design in π-electronic systems is introduced.

## Key findings

- The dianion of the complex shows diradical properties confirmed by ESR and near-infrared absorption.
- Singlet–triplet energy gaps are modulated by coexisting cations and bridging boron moieties.
- Thermal excitation from singlet to triplet diradical states was observed via variable-temperature ESR.

## Abstract

A quinonoidal dipyrrolyldiketone catecholate‐boron complex, with two pyrrole‐quinonemethide moieties bridged by a six‐membered cross‐conjugated unit, was synthesized to modulate the diradical character of the dianion formed upon deprotonation. The dianionic species exhibited near‐infrared absorption and electron spin resonance (ESR) signals, confirming the diradical properties. Variable‐temperature (VT) ESR spectra suggest the thermal excitation from the ground‐state singlet diradical to the triplet diradical, providing singlet–triplet energy gaps modulated by coexisting cations and bridging boron moieties.

A quinonoidal dipyrrolyldiketone boron complex with an orthogonally arranged catechol unit in the dianionic form exhibited diradical properties, as observed from the singlet–triplet energy gaps (ΔE
ST) that were modulated by coexisting countercations. ΔE
ST values were controlled by the bridging boron moieties in the dianion diradicals.