Constructing Excitation‐Wavelength‐Dependent TADF‐Phosphorescence in Polymorphic Compound via Tunable Twisted Intramolecular Charge Transfer

Abstract Excitation‐wavelength‐dependent emission (Ex‐De) materials based on host‐guest systems have garnered significant interest in anticounterfeiting and information encryption applications. Herein, a method is proposed to construct Ex‐De materials by regulating the degree of twisted intramolecular charge transfer (TICT) in polymorphic molecules. Specifically, anthraquinone derivative PCzAQ is employed as TICT‐active guest molecule, while dimethyl terephthalate (DTT) serves as the host. The spray‐coated PCzAQ@DTT@paper sample exhibits yellow and orange emissions under 254 and 365 nm excitation, respectively. Photophysical characterization reveals that the yellow emission originates from thermally activated delayed fluorescence (TADF), while the orange emission is attributed to phosphorescence. The underlying mechanism involves interactions between the excited‐state DTT (S 1 DTT ) (Ex < 310 nm) and PCzAQ molecules, which become stronger, restricting molecular twisting and result in TADF emission. In contrast, the interaction between the ground‐state DTT (S 0 DTT ) (Ex > 310 nm) and PCzAQ molecules weakens, promoting TICT, accelerating intersystem crossing (ISC) process, and leading to phosphorescence emission. Additionally, the application of Ex‐De materials in anticounterfeiting and information security is successfully validated. This work highlights the crucial role of molecular conformation in governing the emission properties of luminescent materials and provides valuable insights for advancing the development of Ex‐De materials.