Effect of π···π Interactions of Donor Rings on Persistent Room-Temperature Phosphorescence in D₄–A Conjugates and Data Security Application

Organic room-temperature phosphorescence (RTP) materials with persistent RTP (PRTP) have attracted huge interest in inks, bioimaging, and photodynamic therapy. However, the design principle to increase the lifetime of organic molecules is underdeveloped. Herein, we show donor­(D4)–acceptor­(A) molecules (TOEPh, TOCPh, TOMPh, TOF and TOPh) with similar orientation of donor rings in aggregates that cause a large number of noncovalent interactions. We observed that TOEPh, TOCPh, TOMPh and TOF showed PRTP, whereas TOPh showed only phosphorescence emission (ΦP = ∼11%) with no PRTP property at ambient conditions. The spectroscopic and single-crystal X-ray analyses confirm the molecular assembly via J-aggregation with a face-to-face orientation of the donor rings. The crystal structure analysis (TOEPh, TOCPh, TOMPh, TOF) reveals that moderate π···π interactions (3.706 to 4.065 Å) between the donor rings cause the enhancement of the phosphorescence lifetime (26 to 245 ms), whereas the short phosphorescence lifetime (12 ms) of TOPh was observed because of the absence of π···π interactions. We found that TOEPh shows a long lifetime (245 ms) as compared to other derivatives because of the presence of ethoxy (−OEt) groups that enables spin–orbit coupling caused by strong lone pair (O)···π interactions present in the molecule. Utilizing the PRTP feature of TOEPh and the fluorescence emission of TOPh, we have shown data security applications in poly­(methyl methacrylate).具有持久室温磷光（PRTP）特性的有机室温磷光（RTP）材料，已在油墨、生物成像与光动力治疗领域引发广泛研究兴趣。然而，当前用于提升有机分子磷光寿命的设计原理仍有待完善。本文中，我们报道了一系列给体(D4)-受体(A)型分子（TOEPh、TOCPh、TOMPh、TOF及TOPh），这类分子的聚集体中给体环具有相似取向，可形成大量非共价相互作用。实验观测显示，TOEPh、TOCPh、TOMPh与TOF均表现出持久室温磷光（PRTP）性能，而TOPh仅能产生磷光发射（磷光量子产率ΦP≈11%），在常温环境下无持久室温磷光特性。光谱表征与单晶X射线衍射分析证实，这些分子通过J聚集方式组装，给体环呈面对面堆叠取向。对TOEPh、TOCPh、TOMPh及TOF的晶体结构分析表明，给体环之间存在强度适中的π···π相互作用（作用距离3.706~4.065 Å），可将磷光寿命提升至26~245 ms；而TOPh因缺乏π···π相互作用，其磷光寿命仅为12 ms。我们发现，相较于其他衍生物，TOEPh拥有更长的磷光寿命（245 ms），这是由于其分子中含有乙氧基(-OEt)基团，该基团可通过分子内强孤对(O)···π相互作用诱导自旋轨道耦合效应。依托TOEPh的持久室温磷光特性与TOPh的荧光发射性能，我们展示了其在聚甲基丙烯酸甲酯（poly(methyl methacrylate)）中的数据安全应用。