Highly Efficient Red Organic Light-Emitting Diodes Using Methylcyclohexylpyran-Containing Emitters

To display full-color, blue-, green-, and red-light-emitting materials are required, and one of the major challenges for OLED research is to develop red-light fluorescent emitters with high luminous efficiency and ideal color purity. On the other hand, it is difficult to develop new red fluorescent emitters with excellent electroluminescence properties and a saturated red color because of the significant concentration quenching by the self aggregation in most fluorescent red emitters. Therefore, considerable efforts have been made to develop efficient red fluorescent materials by preventing concentration quenching through the incorporation of sterically bulky moiety in the emitters. A number of red fluorescent dyes have been synthesized but 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7, -tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) is still the most efficient and studied. In these materials, tert-butyl groups on pyran moiety have large steric hindrance due to its non-coplanar configuration, leading to a decrease in the molecular aggregation in the solid state. This helps improve the efficiency of red fluorescent OLED by reducing concentration quenching in the solid state. On the other hand, red fluorescent emitters require further improvement in terms of the efficiency, lifetime and color chromaticity