Polymorphic Pure Organic Luminogens with Through-Space Conjugation and Persistent Room-Temperature Phosphorescence

Graphical Spatial relations : A pure organic luminogen (AN-MA) with isolated small conjugates and effective through-space conjugation was obtained through facile Diels–Alder cycloaddition. Owing to its flexible structure, two polymorphs were readily obtained. These exhibit bright visible emission and persistent room-temperature phosphorescence ( p -RTP) (see figure). Pure organic luminogens with persistent room-temperature phosphorescence ( p -RTP) have attracted increasing attention owing to their vital significance and potential applications in security inks, bioimaging, and photodynamic therapy. Previously reported p -RTP luminogens normally possessed through-bond conjugation. In this work, we report a pure organic luminogen, AN-MA, the Diels–Alder cycloaddition adduct of anthracene (AN) and maleic anhydride (MA), which possesses isolated phenyl groups and an anhydride moiety. AN-MA exhibits aggregation-enhanced emission (AEE) characteristics with efficiency of approximately 2 % and up to 8.5 % in solution and crystals, respectively. Two polymorphs of AN-MA were readily obtained that were able to generate UV emission from individual phenyl rings together with bright blue emission owing to the effective through-space conjugation. Moreover, p -RTP with a lifetime of up to approximately 1.6 s was obtained in the crystals. These results not only reveal a new system with both fluorescence and RTP dual emission but also suggest an alternative through-space conjugation strategy towards pure organic p -RTP luminogens with tunable emissions.