Highly efficient and stable deep-blue room temperature phosphorescence via through-space conjugation

Efficient blue and deep-blue room temperature phosphorescence (RTP) is still a great challenge due to the difficulties in populating and stabilizing the excitons in relatively high-lying states. Inorganic boric acid, lacking conventional luminophores in its structure, is generally not considered as efficient material for RTP. In this work, we illustrated how to make deep-blue RTP materials with both high emission efficiency (phosphorescence quantum yield of 45%) and an ultralong lifetime (2.9 s) through a heat treatment strategy. Moreover, a throughspace conjugation assisted energy transfer and rigidification mechanism was proposed for explaining the simultaneous promoting of emission lifetime and efficiency. In addition, the deep-blue RTP materials displayed excellent stability against restrict external environments (such as high concentration acid, alkali, oxidant, reductant and organic solvents). Benefiting from these high-performance RTP materials, multi-level information encryption under harsh conditions was demonstrated. The research results thus provide a universal principle and strategy for designing stable and efficient blue RTP materials, which also extend their applications in various environments.