Polymerization-Inhibited Twisted Intramolecular Charge Transfer for Strong Molecular Aggregate Emission

Abstract

Molecular fluorophores exhibiting intramolecular charge transfer (ICT) processes are of great interest across diverse fields, as engineering electron donor or acceptor groups enables control over fluorescence intensity and emission color. However, the fluorescence quantum yield is often decreased by the formation of twisted intramolecular charge transfer (TICT) states. Conventional strategies for reducing TICT effects typically require toxic, expensive reagents and complex syntheses. Here, we present a simple and robust approach that leverages electron-rich, rigid polymer chains to suppress the TICT of naphthalimide-based fluorophores, achieving strong molecular emission in aggregate and solid states. The polymerization-inhibited TICT strategy imparts strong aggregation-induced emission (AIE) behavior in the resulting oligomers and polymers, regardless of the inherent AIE activity of the fluorophore, yielding solid-state photoluminescence quantum yields of up to 0.80. Moreover, the TICT inhibition upon aggregation was indicated simultaneously by the significant blue shift of the emission wavelength as well as by the increased fluorescence lifetime. This work establishes a cost-efficient and versatile methodology for developing highly emissive materials with potential in optoelectronics, such as luminescent solar concentrators and waveguides. We anticipate expanding this approach to a wider range of TICT dyes beyond naphthalimide derivatives.