# Simple Substitutions into Donor–Acceptor Radicals to Construct Highly Luminescent Radicals and Solvent-Responsive Ionic Radical Polymers

## TL;DR

Researchers created highly luminescent radicals and solvent-responsive polymers by modifying donor-acceptor radical structures with simple substitutions.

## Contribution

The study introduces new luminescent radical derivatives and solvent-responsive ionic radical polymers through simple structural modifications.

## Key findings

- TTM-Mes-Cz-Mz and TTM-Mes-Dpa-Mz showed high photoluminescence quantum efficiency (80% and 39%, respectively).
- The polymers LT-Cz and LT-Dpa exhibited solid-state PLQE of 39% and 29%, respectively.
- The polymers displayed solvent-responsive luminescence and could return to their original state after solvent evaporation.

## Abstract

Constructing a donor–acceptor (D–A) architecture in luminescent radicals is an effective strategy for enhancing luminescent properties. However, further structural modification of the radical core through the simple substitutions in the framework of D–A radicals remains relatively underexplored. Herein, we synthesized two radical derivatives TTM-Mes-Cz-Mz and TTM-Mes-Dpa-Mz through modification of the TTM unit of TTM-Cz and TTM-Dpa with imidazole and mesitylene groups. These radical derivatives exhibited high photoluminescence quantum efficiency (PLQE) (80% for TTM-Mes-Cz-Mz and 39% for TTM-Mes-Dpa-Mz) and photostability. The radical units were further covalently grafted onto the polymer chains to synthesize ionic radical polymers LT-Cz and LT-Dpa. LT-Cz and LT-Dpa showed PLQE of 39% and 29% in a solid state, respectively. Furthermore, the polymers exhibited solvent-responsive luminescence with dichloromethane and tetrahydrofuran. A significant redshift in emission wavelength and decrease in emission intensity were observed. The polymers could return to their initial state with solvent evaporation. This work advances the exploration of the role of simple substituent modifications in D–A radical systems, thereby enabling highly efficient luminescence in both small-molecule radicals and radical polymers.