Unlocking Robust Multimodal Room‐Temperature Phosphorescence Afterglow Through in Situ Aqueous Cyclodextrin Supramolecular Assembly

ABSTRACT Significant attention has been directed toward pure organic ultralong room‐temperature phosphorescence (OURTP) yet its development is hindered by limited structural adaptability and aqueous instability. Herein, a facile one‐step strategy is presented to fabricate triple‐modal OURTP materials through in situ aqueous noncovalent assembly of α‐cyclodextrin and 4‐biphenylcarboxylic acid. This streamlined protocol directly affords a stable OURTP supramolecular hydrogel with an extraordinary lifetime of 0.94 s, where robust host‐guest encapsulation and synergistic hydrogen bonding collectively stabilize triplet excitons to suppress non‐radiative decay for naked‐eye visible sustained green afterglow. Subsequently, the hydrogel can be dehydrated into solid supramolecules or processed into transparent deep‐eutectic fluids while retaining ambient durable long‐lived afterglow across all forms, resulting in an exceptional phosphorescence lifetime of 1.17 s and a high photoluminescence quantum yield up to 57.8%. This approach overcomes water‐induced quenching and monomorphic limitations, enabling robust and tunable OURTP in multiple macroscopic architectures without complicated chemical derivatization. Capitalizing on these attributes, a green and adaptable platform for cross‐scenario photonic applications ranging from multiphoton phosphorescence imaging to information security is demonstrated. This work will provide a paradigm for translating fundamental supramolecular principles into morphologically adjustable photonic OURTP materials for versatile interdisciplinary demands.