Organic Metastable Hydrogels via In Situ Ionic-Liquid Crystal Stacking for Latching Room-Temperature Phosphorescence.

Stimuli-responsive room-temperature phosphorescence (RTP) materials offer notable potential in smart optoelectronic materials, yet their development is hindered by the persistent stimuli requirement. By drawing inspiration from inorganic metastable systems, we propose a strategy to fabricate organic metastable materials to address this critical challenge. By integrating supersaturated ionic liquids into a polymeric architecture, RTP hydrogels are obtained under transient stimulus, without requiring persistent stimulation. The soft hydrogels switch to a tough crystallized state via in situ stacking of ionic-liquid crystals. A 10 fold enhancement in toughness and a 34 fold increase in phosphorescence lifetime are achieved, compared to their metastable counterparts. The mechanical reinforcement stems from confined segments and entangled chains caused by in situ stacked ionic-liquid crystals, while the intertwinement of polymer chains further promotes the denser stacking of ionic-liquid crystals to produce long-lived RTP. Leveraging the advantage of 2D correlation spectroscopy in elucidating dynamic mechanisms, we map the microscopic response order of different groups in the crystallization process of ionic liquids and reveal the aforementioned mechanism at the atomic level. This work not only provides a design paradigm for addressing the challenge of transient response in existing stimuli-responsive RTP materials but also charts a route for developing organic metastable materials to unlock unprecedented functionality.