Efficient and long-lived room temperature phosphorescence materials via melt-injection reactions

Developing efficient, long-lasting room-temperature phosphorescence (RTP) materials via a simple synthesis strategy remains highly desirable yet challenging. Herein, we report a melt-injection reaction for the synthesis of RTP materials, wherein guest molecules and paraformaldehyde are injected into molten urea. Strikingly, this approach transforms the originally weak emission of guest molecules into RTP materials with a photoluminescence quantum yield of 76 % and an emission lifetime of 4.6 s. The efficient and long-lived RTP are attributed to a matrix stabilization mechanism: upon injecting formaldehyde into molten urea, a urea-formaldehyde (UF) matrix forms in situ, concomitantly incorporating guest molecules. Hydrogen bonding between the UF matrix and guest molecules drives the formation of cross-linking networks, which not only narrow the energy gap between singlet and triplet states but also restrict guest molecular motion. Furthermore, the rigid UF matrix shields triplet excitons from quenching by oxygen and water, synergistically enhancing RTP performance. As a proof-of-concept application, these RTP materials were employed as photo conversion layers to fabricate information encryption devices. This study provides new insights into RTP material design and highlights their promising potential in information security, chemical sensing, and bio-imaging.