Multifunctional Fluorescent Main-Chain Charged Polyelectrolytes Synthesized by Cascade C–H Activation/Annulation Polymerizations

Fluorescent
polyelectrolytes have attracted enormous attention
as functional polymer materials. In contrast with the widely studied
conjugated polyelectrolytes with ionic groups in side chains, fluorescent
main-chain charged polyelectrolytes (MCCPs) have rarely been explored
due to the large synthetic difficulty. Herein, we develop a facile
and atom-economical N-heterocyclic carbene-directed
cascade C–H activation/annulation polymerization strategy that
can transform readily available imidazolium substrates and internal
diynes into multifunctional fluorescent MCCPs with complex structures
and high molecular weights (absolute Mn up to 135 600) in nearly quantitative yields. The presence
of multisubstituted polycyclic N-heteroaromatic cations
in polymer backbones endow the obtained MCCPs with excellent solution
processability, high thermal stability, and dual-state efficient fluorescence
in both solution and aggregate states. Benefiting from the strong
electron-withdrawing capability of the cationic heterocycles in main
chains, multicolored aggregate-state fluorescence can be readily achieved
by modifying the substituents around the cationic ring-fused core.
Taking advantage of the good photosensitivity of the fluorescent MCCP
thin films, multiscale and high-resolution fluorescent photopatterns
with different colors can be facilely prepared with potential applications
in optical display devices and anticounterfeiting systems. Moreover,
the strong electrostatic interactions of these cationic MCCPs with
anionic polyelectrolytes enable them to form multicolored fluorescent
interfacial polyelectrolyte complexation microfibers with directly
visualized internal structures. Such flexible microfibers can be further
made into diversified forms of fiber-based macroscopic patterns or
painting.