Effect of π···π Interactions of Donor Rings on Persistent Room-Temperature Phosphorescence in D-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(D)-acceptor(A) molecules (, , , and ) with similar orientation of donor rings in aggregates that cause a large number of noncovalent interactions. We observed that , , and showed PRTP, whereas showed only phosphorescence emission (Φ = ∼11%) with no PRTP property at ambient conditions. The spectroscopic and single-crystal X-ray analyses confirm the molecular assembly via -aggregation with a face-to-face orientation of the donor rings. The crystal structure analysis (, , , ) 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 was observed because of the absence of π···π interactions. We found that 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 and the fluorescence emission of , we have shown data security applications in poly(methyl methacrylate).