Pyridine linked fluorene hybrid bipolar host for blue, green, and orange phosphorescent organic light-emitting diodes toward solution processing

摘要

Herein, a new series of ambipolar host materials is synthesized, which features a pyridine core and triphenylamine or carbazole arm combined in a non-conjugated configuration. Theoretical calculation resuLts show that their HOMO/LUMO distribution is adjusted from an overlapped state to partially and thoroughly separated states, and their hole/electron transportation ability and energy levels are also tuned, in addition to their triplet energy level varying from 2.38 to 2.87 eV. Thermogravimetric analysis and DSC measurement resuLts display a high thermal decomposition temperature of 420-490 degrees C and a wide glass transition temperature range of 160-173 degrees C, along with excellent reversible redox behavior in electrochemical processes. Utilizing the pure host of 4',4'''-(pyridine-2,6-diylbis(9H-fluorene-9,9-diyl)bis(N,N-diphenyk[1,1'-biphenyE]-4-amine), blue organic Eight-emitting diodes (OLEDs) show a high efficiency of 18.5 cd A(-1) and 13.6 Em W-1 compared with 16.3 cd A(-1) and 11.6 Em W-1 for the cohost diodes, respectively. Additionally, orange phosphorescent device from the N,N-((pyridine-2,6-diylbis(9H-fLuorene9,9-diyl))bis(4,1-phenyEene))bis(N-phenyEnaphthaLen-1-amine) cohost shows higher efficiency than the single host devices with a maximum Luminous efficiency of 37.3 cd A(-1) in a high brightness region of around 12 680 cd m(-2), which makes it one of the most efficient orange OLEDs containing a solution processed single emissive Layer structure. Significantly, their efficiency roll-off is greatly suppressed at high Luminance, particularly for the orange device with a 3.21% decrease in efficiency from the maximum to a high brightness of 10 000 cd m(-2). This work provides a useful guide for molecular design toward soLution processed OLEDs.