Organic Afterglow Emitters for Visual Observation of Hydrogel Formation in Biomedical Systems

Biomedical hydrogels are integral to a wide range of applications, with their efficacy critically hinging on precise delivery and successful gelation at targeted sites. Nevertheless, existing technologies that provide reliable, visual confirmation of gelation and accurate localization remain very limited. Here organic afterglow emitters are reported that are designed with small phosphorescence rate (k_P ≈ 0.04 s^-1), small nonradiative decay rate (k_nr ≈ 0.01 s^-1), and controllable oxygen quenching rate (k_q). The organic emitters exhibit no afterglow in liquid state under ambient conditions. Upon hydrogel formation, the organic emitters, embedded within the as-formed biomedical hydrogel, demonstrate bright and persistent afterglow with phosphorescence lifetimes extending up to 15.82 s. This gelation-induced afterglow, characterized by a high on/off contrast, facilitates a visual observation of successful hydrogel formation and precise localization of biomedical hydrogels. In-depth studies reveal that, within the biomedical hydrogel, the diffusion of oxygen is significantly impeded and oxygen concentration is also reduced, leading to a substantially small k_q of the organic emitter (≈0.02 s^-1) and subsequent emergence of the afterglow. This study presents a novel afterglow-based approach for visualizing hydrogel formation and localization, and meanwhile offering an innovative strategy to achieve high-performance organic afterglow in soft matter systems.