Tuning the Optoelectronic Properties of Carbazole/Oxadiazole Hybrids through Linkage Modes: Hosts for Highly Efficient Green Electrophosphorescence

摘要: A series of bipolar transport host materials: 2,5-bis(2-(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (o-CzOXD) (1), 2,5-bis(4-(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (p-CzOXD) (2), 2,5-bis(3-(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (m-CzOXD) (3) and 2-(2-(9H-carbazol-9-yl)phenyl)-5-(4-(9H-carbazol-9-yl)phenyl)-1,3,4-oxadiazole (op-CzOXD) (4) are synthesized through simple aromatic nucleophilic substitution reactions. The incorporation the oxadiazole moiety greatly improves their morphological stability, with T-d T-g in range 428-464 degrees C 97-133 C, respectively. ortho meta positions 2,5-diphenyl-1,3,4-oxadiazole linked hybrids (1 3) show less intramolecular charge transfer a higher triplet energy compared to para-position analogue (2). four compounds exhibit similar LUMO levels (2.55-2.59 eV) other derivatives, whereas HOMO vary from 5.55 eV 5.69 eV, depending on linkage modes. DFT-calculation results indicate that 1, 3, 4 have almost complete separation at hole- electron-transporting moieties, while 2 exhibits only partial possibly due transfer. Phosphorescent organic light-emitting devices fabricated using 1-4 as hosts green emitter, Ir(ppy)(3) or (ppy)(2)Ir(acac), guest good excellent performance. Devices hosted by o-CzOXD (1) achieve maximum current efficiencies (eta(c)) high 77.9 cd A(-1) for 64.2 (ppy)(2)Ir(acac). device performance may be attributed well-matched between hole-transport layers, spatial levels.