Engineering Color‐Tunable Photochromic Ultra‐Long Room Temperature Phosphorescence Polymer Films by Regulating Intramolecular Charge Transfer of Nonlinear Pyridinium Units

Abstract Dynamic photochromic ultra‐long room‐temperature phosphorescent (URTP) materials are promising for advanced anti‐counterfeiting and information encryption due to their stimuli‐responsive, tunable optical properties. However, developing high‐performance, color‐tunable photochromic URTP polymers with clear mechanistic insight remains challenging. Here, this is addressed by strategically embedding nonlinear pyridinium units—capable of tunable intramolecular charge transfer (ICT)—into a rigid polyvinyl alcohol (PVA) matrix. Spectroscopic analyses reveal that photoexcitation induces ICT‐driven charge separation, forming long‐lived triplet charge‐transfer (CT) states with distinct energy, enabling multicolor URTP emission. The PVA matrix stabilizes these triplet CT states and facilitates CT‐mediated electron transfer from hydroxyl groups to pyridinium acceptors, generating stable radicals responsible for reversible photochromism. Furthermore, cross‐linking the pyridinium‐doped PVA networks with boric acid simultaneously enhances the phosphorescence lifetime (up to 0.96 s) and quantum efficiency (up to 27.8%) while preserving high‐contrast reversible photochromic behavior. These multifunctional films demonstrate applications in multilevel anti‐counterfeiting, rewritable patterning, and secure information encryption. This work provides a robust design strategy for stimuli‐responsive photochromic URTP polymers.