Fluorene-based Tröger’s base analogues: Potential electroluminescent materials

Two new Λ-shaped fluorene-based Tröger’s base (TB) analogues with aryl substitutions are successfully synthesized and their photophysical and electroluminescent properties are examined in detail. Both compounds exhibit strong fluorescence emission in dilute solutions and aggregated states. Some abnormal photophysical behaviors have been observed; that is, the amorphous films of the two TB analogues show multiple blue–green emissions similar to the emissions of some polyfluorenes and oligofluorenes, while both the dilute solutions and the polycrystalline powders of two compounds show single blue–violet emission. Furthermore, the emissions of the amorphous film are obviously red-shifted in comparison with the polycrystalline powders. Organic light emitting diodes (OLEDs) using the two compounds as non-doped emitters with device structure of ITO/NPB (30 nm)/TBFB-BP or TBFB-FB (40 nm)/TPBI (40 nm)/LiF (1 nm)/Al (80 nm) were fabricated and high brightness (22047 cd/m2 for TBFB-BP and 13434 cd/m2 for TBFB-FB), high efficiency (2.78 cd/A, 1.82 lm/W for TBFB-BP and 2.76 cd/A, 1.93 lm/W for TBFB-FB) and low turn-on voltage (4.6 V for TBFB-BP and 4.5 V for TBFB-FB) were obtained. Our studies suggest that TB analogues could be excellent light emitting materials for OLED applications.