Tetra-carbazole substituted spiro[fluorene-9,9′-xanthene]-based hole-transporting materials with high thermal stability and mobility for efficient OLEDs

Two spiro[fiuorene-9,9'-xanthene]-centered (SFX), tetra-carbazole substituted molecules 2,2',7,7'-tetrakis(N, N-carbazole)-spiro(fluorene-9,9'-xanthene) (SFX-Crl) and 2,3',6,'7-tetrakis(N, N-carbazole)-spiro(fiuorene-9,9'-xanthene) (SFX-Cr2) were synthesized, and the effect of the position of carbazole substitutes on bulk properties, such as photophysical and electrochemical properties, thermal stability and hole mobility were investigated. The results implied both these two materials have excellent thermal stability and hole mobility than those of N, N'-Bis(naphthalen-l-y1)-N, N'-bis(phenyl)-benzidine (NPB). To explore the application, organic light -emitting diodes (OLEDs) with SFX-Crl and SFX-Cr2 as hole transport layer were fabricated and characterized. SFX-Cr2 garnered the highest glass transition temperature of 130.1 degrees C and hole mobility of 1.57 x 10(-3) cm(2) V-1 S-1, yielding an appreciated OLED performance in terms of a maximum current efficiency of 55.8 cd A(-1), a maximum power efficiency of 46.6 1 m W-1, and a maximum external quantum efficiency of 16.3%. (C) 2017 Elsevier Ltd. All rights reserved.