Visible‐Light‐Excited Ultralong Organic Phosphorescence by Manipulating Intermolecular Interactions

Visible light is much more available and less harmful than ultraviolet light, but ultralong organic phosphorescence (UOP) with visible‐light excitation remains a formidable challenge. Here, a concise chemical approach is provided to obtain bright UOP by tuning the molecular packing in the solid state under irradiation of available visible light, e.g., a cell phone flashlight under ambient conditions (room temperature and in air). The excitation spectra exhibit an obvious redshift via the incorporation of halogen atoms to tune intermolecular interactions. UOP is achieved through H‐aggregation to stabilize the excited triplet state, with a high phosphorescence efficiency of 8.3% and a considerably long lifetime of 0.84 s. Within a brightness of 0.32 mcd m −2 that can be recognized by the naked eye, UOP can last for 104 s in total. Given these features, ultralong organic phosphorescent materials are used to successfully realize dual data encryption and decryption. Moreover, well‐dispersed UOP nanoparticles are prepared by polymer‐matrix encapsulation in an aqueous solution, and their applications in bioimaging are tentatively being studied. This result will pave the way toward expanding metal‐free organic phosphorescent materials and their applications.