Improved red dopants for organic electroluminescent devices

Abstract

Abstract A t ‐butyl substituted red fluorescent dye, 4‐(dicyanomethylene)‐2‐ t‐butyl ‐6‐(1,1,7,7‐tetramethyljulolidyl‐9‐enyl)‐4 H ‐pyran (DCJTB), has been found to be an excellent dopant in AIQ 3 which produces a highly efficient organic EL device with improved red chromaticity. Unlike 4‐(dicyanomethylene)‐2‐ methyl ‐6‐(1,1,7,7‐tetramethyljulolidyl‐9‐enyl)‐4 H ‐pyran (DCJT), DCJTB can be synthesized in a pure form directly from the unsymmetrical 4‐(dicyanomethylene)‐2‐( t ‐butyl)‐6‐methyl‐4 H ‐pyran without the contamination of the non‐fluorescent bis ‐condensation byproduct which is prevalent in the DCJT preparation. Both photoluminescence and electroluminescence in the solid films of DCJTB in AlQ 3 are modestly enhanced by the extra t‐butyl substitution as a result of a reduction in the effect of concentration quenching. The operation stability of the DCJTB doped EL device is superior, having a half‐life of over 5,000 h driven at an initial brightness > 400 cd/m 2 .