Surface-Induced Photophysical Enhancement of Conjugated Polyelectrolytes on Cellulose Nanocrystals: A Single-Particle Study

Conjugated polyelectrolytes possess unique photophysical properties, yet their brightness and photostability are significantly hindered in water as they adopt a collapsed state. In this study, we present a strategy to overcome these limitations by assembling short poly(phenylene ethynylene)-based conjugated polyelectrolytes onto cellulose nanocrystals, forming brighter fluorescent hybrid nanoparticles. This assembly process suppresses excimer-like species and promotes disaggregated, highly fluorescent, and photostable conformation whose emission is shifted to 450 nm. By analyzing the intensity-time traces and emission spectra at both the ensemble and single-particle levels, we unraveled the underlying mechanism of the enhanced photophysical properties of the conjugated polyelectrolytes. The cellulose nanocrystal surface facilitated the assembly of individual polymer chains into ordered aggregates, leading to improved overall photophysical properties. These findings highlight the potential of cellulose-based nanostructures as a platform for tuning and stabilizing the emission properties of conjugated materials in aqueous media.