Supramolecular Assembly‐Driven Photofluorochromism Enables Time‐Encoded Transient Encryption

Stimuli‐responsive luminescent materials offer dynamic optical outputs for advanced information security, yet achieving programmable fluorescence color evolution in water using a single optical input remains challenging. We developed a water‐soluble zwitterionic monomer, 2‐(pent‐4‐en‐1‐yl)isoquinolin‐2‐ium‐5‐sulfonate (IQIS), that exhibits pronounced photofluorochromism under ultraviolet (UV) irradiation. Its fluorescence evolves from blue to green, accompanied by an increase in the overall fluorescence quantum yield from 3.5% to 17.3%. Mechanistic studies reveal that IQIS is weakly pre‐associated in water, while UV irradiation promotes the growth, densification, and packing reorganization of these loose molecular clusters. The resulting long‐wavelength emission exhibits distinct aggregation‐dependent photophysical characteristics and is consistent with an aggregate‐associated excited state with enhanced intermolecular charge‐transfer character. By programming the kinetics of this supramolecular reorganization in different polymeric architectures, high‐resolution grayscale patterns with time‐evolving optical outputs can be generated. Under continuous UV irradiation, the same light used for fluorescence readout simultaneously drives the optical evolution, causing initially visible information to progressively fade and ultimately disappear without an additional stimulus. This single‐input, self‐evolving behavior enables a “Snapchat‐like” transient encryption mode and provides a strategy for spatiotemporal information encoding based on kinetically programmed supramolecular photofluorochromism.