Synthesis and Applications of Excimer Host Materials Based on 2,4,6-Triphenyl-1,3,5-triazine and Fluorene Moieties

Abstract

Three new bipolar derivatives based on 2,4,6-triphenyl-1,3,5-triazine and fluorene moieties, namely FTRZ, pTFTRZ and mTFTRZ were designed and synthesized by using 9-(4-(hexyloxy) phenyl) -9H-fluorene, 2-bromo-4,6-diphenyl-1,3,5-triazine, 2,4,6-tris(4-bromophenyl) -1,3,5-triazine, and 2,4,6-tris(3-bromophenyl) -1,3,5-triazine through palladium-cata-lyzed cross-coupling reaction, which were reported as hosts for thermally activated delayed fluorescence organic light-emitting diodes (OLEDs). The 1 H NMR, 13 C NMR and MALDI-TOF-MS spectra were used to characterize the chemical structure of compounds FTRZ, pTFTRZ and mTFTRZ. Their thermal, photophysical and electrochemical properties as well as electroluminescent device performance were thoroughly investigated to correlate the optoelectronic properties with the topology-varied molecular structure. The thermal decomposition temperatures of compounds FTRZ, pTFTRZ and mTFTRZ are 427, 446 and 424℃ and their glass transition temperatures of compounds pFTRZ and mTFTRZ are 120 and 103℃, respectively. The optical band gaps of compounds FTRZ, pTFTRZ and mTFTRZ in toluene solution are 3.24, 3.29 and 3.24 eV, and their triplet energy levels are 3.04, 3.11 and 3.05 eV, respectively. Due to the π-π interaction between 2,4,6-triphenyl-1,3,5-triazine planes, compounds FTRZ, pTFTRZ and mTFTRZ form excimer in the thin film state. The electroluminescent properties of OLEDs using compounds FTRZ, pTFTRZ and mTFTRZ as the hosts and 2,4,5,6-tetrakis(carbazol-9-yl) -1,3-dicyanobenzene as the guest emitter were investigated. The green OLED of compound FTRZ as host material shows a peak emission at 510 nm with a maximum current efficiency of 6.7 cd/A, a maximum external quantum efficiency of 2.07% and a maximum brightness of 35718 cd/m 2 . The efficiency roll-offs of the OLEDs hosted by compounds FTRZ and pTFTRZ at 20000 cd/m 2 are 3% and 2%, which are much better than the same device hosted by compound mTFTRZ.