Efficient blue emission from pyrazoline organic light emitting diodes

Two kinds of pyrazoline derivatives, 3-(4-chlorophenyl)-4,5-dihydro-1,5-diphenyl 1-H-Pyrazole, (P1) and 3-(4-methoxyphenyl)-4,5-dihydro-1,5-diphenyl 1-H-Pyrazole (P2) were synthesized. They showed efficient photoluminescence (PL) in both solid state and solution. The emission peak of P1 was observed at 450 nm and that of P2 was at 432 nm. Two types of organic electroluminescent devices (OELDs) using these materials as emitting layer were fabricated, one is a three-layered structure device fabricated by dry process and another is a single or double layer structure device fabricated by a wet technique. These materials were found to function as good blue light-emitting materials for OELDs. The device with a structure of ITO/TPD/P1/Alq3/Mg:Ag showed a turn-on voltage of 3.5 V, while the device using P2 instead of P1 gave a turn-on voltage of 3 V, both of them give green light resulting from Alq3 and the maximum light intensity was 5710 cd/m2 under driving voltage of 8.5 V. The device of ITO/PVK+P1/Alq3/Al emitted bright blue light resulting from P1. It exhibited a maximum luminance of 200 cd/m2 at a driving voltage of 12 V, and the device of ITO/PVK+P2/Al exhibited blue light of 200 cd/m2 at a driving voltage of 11 V.