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, (P-1) and 3-(4-methoxyphenyl)-4,5-dihydro-1,5-diphenyl 1-H-Pyrazole (P-2) were synthesized. They showed efficient photoluminescence (PL) in both solid state and solution. The emission peak of P-1 was observed at 450 nm and that of P-2 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/P-1/Alq(3)/Mg:Ag showed a turn-on voltage of 3.5 V, while the device using P-2 instead of P-1 gave a trim-on voltage of 3 V, both of them give green light resulting from Alq(3) and the maximum light intensity was 5710 cd/m(2) under driving voltage of 8.5 V. The device of ITO/PVK + P-1/Alq(3)/Al emitted bright blue light resulting from P-1. It exhibited a maximum luminance of 200 cd/m(2) at a driving voltage of 12 V, and the device of ITO/PVK + P-2/Al exhibited blue light of 200 cd/m(2) at a driving voltage of 11 V. (C) 2000 Elsevier Science S.A. All rights reserved.