TADF용 Cyclohexane-1,1-diyldibenzene계 Ambipolar Host에 관한 연구

Abstract

In this paper, a series of Cyclohexane-1,1-diyldibenzene (spacer) derivatives 9-(4-(1-(4-(diphenylphosphoryl)phenyl)cyclohexyl)phenyl)-9 H-carbazole (AH1), 9-(4-(1-(4-(phenylsulfonyl)phenyl)cyclohexyl)pheny l)-9H-carbazole (AH2), 9-(4-(1-(4-(diphenylphosphorothioyl)phenyl)cyc lohexyl)phenyl)-9H-carbazole (AH3), 9-(4-(1-(4-(pyrazin-2-yl)phenyl) cyclohexyl)phenyl)-9H-carbazole (AH4), 9-(4-(1-(4-(pyridin-2-yl)phen yl)cyclohexyl)phenyl)-9H-carbazole (AH5), 9-(4-(1-(4-(4,6-diphenyl-1,3 ,5-triazin-2-yl)phenyl)cyclohexyl)phenyl)-9H-carbazole (AH6) were designed and synthesized as ambipolar host materials for TADF (Thermally Activated Delayed Fluorescence) In these molecules, modified carbazole and phosphine, sulfur and pyridine derivative substituents were used as electron-donating and electron–withdrawing groups. By designing the molecular structures ideally, greatly changes in host properties were observed.; all of AH series were observed as host materials with a high triplet energy, broad band gap and bipolar charge transport character. Furthermore, 4CzIPN were used as dopant of a green emitter for TADF. Host doped films in 6 wt.% 4CzIPN, all of AH series showed a green emission with wavelengths of 506-515 nm. It is well-known that AH is transferred emission energy to 4CzIPN in a host-dopant system. Because the Cyclohexane-1,1-diyldibenzene have disconnect function of π-conjugated bond as ‘spacer', therefore electron-donating and electron–withdrawing groups retain high triplet energy. As a result, all of AH series has outstanding energy transfer from host to dopant. Even though all of AH series showed delayed fluorescence, AH3 showed the greatest performance of OLED device; A delayed fluorescence lifetime of 3.50 μs was observed under nitrogen atmosphere at room temperature. A EL emission of 511 nm, a brightness of 6600 Cd/m2, a current efficiency of 64.9 Cd/A, a power efficiency of 63.8 Cd/A and an external quantum efficiency of 20.9% were also observed.