Research group of Professor Yan Dongpeng of Beijing Normal University realizes ultra long organic room temperature phosphorescence based on the mechanism of thermal activation delayed fluorescence and resonance energy transfer

In recent years, molecular room temperature phosphorescence (RTP) materials with long-lived excited states and delayed luminescence have been widely concerned in the fields of optical imaging, biotherapy, display, sensing and anti-counterfeiting Compared with the traditional inorganic long afterglow materials, the pure organic RTP system has the advantages of small biological toxicity, easy preparation, good processing performance and low cost However, pure organic RTP materials rarely reach the excited state lifetime of several seconds, which greatly limits its application in luminescence visualization and recognition At present, there are several strategies to realize pure organic RTP: through the introduction of heavy atoms, it can strengthen the orbit rotation coupling and promote the inter system crossing; through the enhancement of system rigidity, it can reduce the non radiation energy loss of three line state However, it is still a great challenge to design and synthesize long-life organic RTP materials which are comparable to inorganic light-emitting systems Recently, the research group of Professor Yan Dongpeng, School of chemistry, Beijing Normal University, based on the idea of thermal excitation energy transfer in the design of inorganic long afterglow system, proposed the mechanism of using thermal activation delayed fluorescence (TADF) to assist f ö rster resonance energy transfer (FRET) to realize ultra long organic RTP In order to confirm the mechanism, the team first selected the organic molecules with suitable energy level matching and orientation, in which the thermal activation delayed fluorescence molecule melamine (me) was used as the energy donor, and the phosphorescent molecules phthalic acid (PA), isophthalic acid (IPA) and p-benzoic acid (TPA) were used as the energy acceptor ）Based on this, three hydrogen bond assembly eutectic model systems (pa-me, ipa-me, tpa-me) were established The schematic diagram and mechanism of ultra long organic RTP (source: Advanced Functional Materials) through the steady-state / transient spectrum technology, the research team found that compared with the precursor, the RTP life of three kinds of eutectic materials is greatly improved, and the phosphorescence life of ipa-me can reach 2S, which is higher than most of the pure organic long afterglow materials reported at present The experimental results show that the increase of phosphorescence lifetime depends on the effective energy transfer from me to receptor (the efficiency is as high as 76%), which proves the assumption of realizing ultra long room temperature phosphorescence under the synergistic effect of TADF and fret, and also provides a new strategy for building pure long afterglow materials In addition, using the characteristics of time-resolved phosphorescence, the research group further developed the application of this kind of materials in the field of information encryption and fingerprint recognition This work was supported by 973 program, National Natural Science Foundation of China and Beijing Natural Science Foundation It was recently published in advanced functional materials (DOI: 10.1002 / ADFM 201807599) Zhou Bo, 2017 master student of School of chemistry, Beijing Normal University, was the first author of this paper.