Bright Free-Radical Emission in Ionic Liquids

It is challenging to achieve stable and efficient radical emissions under ambient conditions. Herein, we present a rational design strategy to protect photoinduced carbonyl free radical emission through electrostatic interaction and spin delocalization effects. The host-guest system is constructed from tricarbonyl-substituted benzene molecules and a series of imidazolium ionic liquids as the guest and host, respectively, whereby the carbonyl anion radical emission can be in situ generated under the light irradiation and further stabilized by electrostatic interaction. More importantly, the anion species and the alkyl chain length of imidazolium ionic liquids show a noticeable effect on luminescence efficiency, with the highest radical emission efficiency is as high as 53.3 % after optimizing the imidazole ionic liquid's structure, which is about four times higher than the polymer-protected radical system. Theoretical calculations confirm the synergistic effect of strong electrostatic interactions and that the spin delocalization effect significantly stabilizes the radical emission. Moreover, such a radical emission system also could be integrated with a fluorescent dye to induce multi-color or even white light emission with reversible temperature-responsive characteristics. The radical emission system can also be used to detect different amine compounds on the basis of the emission changes and photoactivation time.

Automated summary

This study presents a rational design strategy to protect photoinduced carbonyl free radical emission through electrostatic interaction and spin delocalization effects. A host-guest system consisting of tricarbonyl-substituted benzene molecules and imidazolium ionic liquids was constructed, enabling in situ generation and stabilization of carbonyl anion radical emission. The luminescence efficiency was significantly influenced by the anion species and alkyl chain length, with the highest radical emission efficiency being four times higher than a polymer-protected radical system. Theoretical calculations confirmed the synergistic effect of electrostatic interactions and spin delocalization in stabilizing the radical emission.