Efficient blue emission from pyrazoline organic light emitting diodes

Two kinds of pyrazoline derivatives, 3-(4-chlorophenyl)-4,5-dihydro-1,5-dip henyl 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 photoluminescenc e (PL) in both solid state and solution. The emission peak of P-1 was obser ved at 450 nm and that of P-2 was at 432 nm. Two types of organic electrolu minescent devices (OELDs) using these materials as emitting layer were fabr icated, one is a three-layered structure device fabricated by dry process a nd another is a single or double layer structure device fabricated by a wet technique. These materials were found to function as good blue light-emitt ing 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 result ing from Alq(3) and the maximum light intensity was 5710 cd/m(2) under driv ing 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 exhibi ted blue light of 200 cd/m(2) at a driving voltage of 11 V. (C) 2000 Elsevi er Science S.A. All rights reserved.