Red fluorenes as the efficient host emitter for non-doped red organic light-emitting diodes

Abstract

Crystallinic red fluorophores based on donor-acceptor substituted spirofluorene, i.e., PhSPDCV show strong fluorescence in solution (Phi(f) - 70%) as well as in solid state (Phi(f) > 30 %). Non-doped red OLEDs fabricated with PhSPDCV exhibit authentic red (CIE, x = 0.65, y = 0.35) electroluminescence with brightness over 12,000 cd m(-2) (or > 600 cd m(-2) at 20 mA cm(-2)) and remarkable external quantum efficiency as high as 3.6%. On the other hand, the bis-substituted derivatives of spirofluorene BisPhSPDCV show relatively weak fluorescence both in solution (Phi(f) < 20 %) and in solid state (Phi(f) < 10 %). Although saturated red electroluminescence (CIE, x = 0.65, y = 0.34) is also observed, non-doped red OLED containing BisPhSPDCV performs much worse than PhSPDCV OLEDs. Both PhSPDCV and BisPhSPDCV are not amorphous forming loosely packed crystallinic materials in solid state with no intimate pi-pi interaction.