Host‐Guest Systems Enable Efficient Organic Afterglow via a Facile Spraying Method

Unlocking the afterglow properties of the fluorescence molecules at room temperature is an urgent challenge. Herein, inks prepared with dimethyl terephthalate (DTT) and carbazole (Cz) analogs with heteroatom (C, S, and O) substituents on the N as host and guest molecules can be directly sprayed onto different substrates to unlock the excitation‐wavelength dependent (Ex‐De) afterglow characteristics of the guest compound. Additionally, with the increase in the number of lone pair electrons, spin‐orbit coupling (SOC) increases, resulting in a longer afterglow duration lasting up to 4.5 s with Φp>27%. Theory calculations and experiments indicate that the afterglow originated from the interactions between the host and guest molecules restricting the non‐radiative transition of the triplet excitons. Different Ex (with watershed at 310 nm) lead to the variation in the conformation of the S0DTT and S1DTT, which in turn affects the strength of host‐guest interactions and contributes to the Ex‐De characteristics. Benefiting from facile preparation, substrate‐independent applicability, and Ex‐De characteristics, the afterglow samples are demonstrated for applications in multilevel information security fields. This work proposes a general strategy for unlocking the afterglow emission of traditional molecules, which is valuable for the discovery of high‐performance afterglow materials in the future. Using carbazole analogs C, S, and O as guest molecules, with DTT as the host molecule, dissolved in dichloromethane solution and directly sprayed onto various substrates, can construct excitation‐wavelength‐dependent phosphorescent afterglow emission with a duration exceeding 4 s and Φp greater than 27%. The multilevel information encryption is demonstrated.