Probing non-equilibrium inner structure of polymeric nanoparticle via aggregation-induced emission of luminogen

A molecular segregation inside a nanoparticle was crucial for its properties but usually hard to be determined, especially for organic particles. Herein, non-equilibrium polymeric nanoparticles loading a luminogen via an aggregation-induced emission (AIE) were prepared via an instant formation process, flash nanoprecipitation (FNP). Small organic molecules, polymeric excipients, and oily compounds were used as coprecipitants to reveal effects of conjugate moiety, glass transition temperature (T_g), and a condensed state of a coprecipitant on the fluorescence (FL) intensity of the suspension. The results indicated that the addition of a small molecule in a solid state without any conjugate moiety or a polymeric excipient with high T_g would facilitate enhancing the FL intensity, while a coprecipitant with a conjugate moiety or low T_g or in liquid would decrease the intensity. Moreover, this study revealed that the nanoparticle formed via FNP had a randomly packed inner structure where different compositions tended to evenly distribute inside rather than a micellar structure with a phase-separated core-shell one. These findings provided a guide to selecting a suitable coprecipitant for AIE-luminogen nanoparticles in applications. The developed probing method would also benefit for better understanding the particle formation kinetics in FNP.