Water‐Enabled Ultralong Full‐Color Organic Phosphorescence in Hydrogen‐Bonded Frameworks for 4D Encryption and Bio‐Imaging

ABSTRACT Developing water‐stable organic room‐temperature phosphorescence (RTP) materials remains a formidable challenge due to water‐induced quenching. Herein, we present a counter‐intuitive strategy to achieve water‐enhanced ultralong RTP via the in situ encapsulation of carbonyl‐based guests within a rigid hydrogen‐bonded organic framework (HOF). Unlike conventional systems where water acts as a quencher, we demonstrate that water molecules function as pivotal structural reinforcers. Mechanistic studies reveal that water bridges host–guest hydrogen‐bonding sites, constructing a denser network that rigidifies molecular conformation and promotes intersystem crossing. Consequently, phosphorescence intensity peaks at a high water content of 55 wt.%. Significantly, this universal strategy enables full‐color ultralong phosphorescence (from blue to deep red) by tuning guest conjugation‐a rare feat in aqueous media. Benefiting from exceptional physiological stability and biocompatibility, these nano‐sized hybrids overcome intracellular quenching bottlenecks, enabling high‐signal‐to‐noise ratio cellular bio‐imaging. Additionally, applications in 4D encryption and humidity sensing are demonstrated. This work transforms a traditional phosphorescence killer into a synergistic enhancer, offering a novel paradigm for designing high‐performance RTP materials tailored for biological applications.