Pyrazoline derivatives for blue color emitter in organic electroluminescent devices

Electroluminescence (EL) behaviors of four derivatives of pyrazoline as a doping dye in EL device have been studied. Photoluminescence (PL) in solution and as solid films have also been studied. It was observed that the pyrazoline derivatives show very strong PL and EL. On the contrary, the non-cyclic hydrazone compounds containing the same conjugated moiety as in pyrazoline do not emit strongly in solution or in solid state. The pyrazoline derivatives with the phenyl group at the 5-position possess good film-forming properties, which might be due to their non-planar structure. On the other hand, the pyrazoline derivatives without the phenyl group at the 5-position are more planar and thus aggregate easily. These properties lead to degradation in the device performance.