Linkage engineering in hosts for dramatic efficiency enhancement of blue phosphorescent organic light-emitting diodes.

Higher triplet energy and balanced charge mobility is two key factors for high-efficiency host materials of phosphorescent organic light-emitting diodes (PhOLED), which are integrated in a carbazole-diphenylene-fluorene hybrid FDPCz2 (9,9'-(4',4"-(9H-fluorene-9,9-diyl)bis(biphenyl-4',4-diyl))bis(9H-carbazole)) on the basis of indirect linkage strategy. Owing to rationally spatial allocation of conjugation blocking and extension for diphenylene linkages, FDPCz2 achieves both high triplet energy of 2.97 eV and favorable charge mobility by order of 6.3 × 10(-6) cm(2) V(-1) s(-1). Compared to conventional hosts and a short-conjugated analogue FPCz2 (9,9'-(4,4'-(9H-fluorene-9,9-diyl)bis(4,1-phenylene)) bis(9H-carbazole)), FDPCz2 dramatically elevated device efficiencies with peak values of 40.6 cd A(-1) and 20.2% for blue PhOLEDs.