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

Abstract

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 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.

Manipulating the Stacking of Triplet Chromophores in the Crystal Form for Ultralong Organic Phosphorescence

“…Broadly defined, molecular packing involves the stacking between various groups. Some groups, such as carbazole, phenothiazine,– etc., favor triplet excited states and could be regarded as triplet chromophores for manipulating phosphorescence generation, whereas others can be seen as functional groups that may be used to manipulate molecular packing by tuning intermolecular interactions (Figure a). It is important to identify which group, when stacked in crystal form, is essential for UOP generation.…”

Multiple Luminescence Responses towards Mechanical Stimulus and Photo‐Induction: The Key Role of the Stuck Packing Mode and Tunable Intermolecular Interactions

“…However, so far, no ML luminogens have been reported to be accompanied with the photo‐induced RTP. Actually, the multiple response of luminogens in the solid state towards photo‐induction and mechanical stimulus could reveal very important information and considerations about molecular packing and its possible tunability, together with the related technological application as smart materials, in addition to the deep understanding of the ML and RTP processes…”

Pure Organic Persistent Room‐Temperature Phosphorescence at both Crystalline and Amorphous States

“…Furthermore, persistent RTP ( p ‐RTP) with naked eye visible emission after ceasing the excitation is even difficult to achieve, despite it has diverse promising applications in advanced OLEDs, bioimaging, encryption and anticounterfeiting ,. So far, increasing examples have been explored in host‐guest systems,, H‐aggregates,,, crystals and even nonconventional luminogens free of aromatics,, the mechanism and rational design strategy, however, remain open questions.…”