Properties of a new pyrazoline derivative and its application in electroluminescence

As evaporated thin film and in solution, the absorption spectra, photolumin escence, electrochemistry and electroluminescence of the newly synthesized 1,3-diphenyl-5-pyren-2-yl-4,5-dihydro-1H-pyrazole (DPP) were investigated. The absorption spectra cover the whole near-ultraviolet region. At lower co ncentrations, the fluorescence emission is at 415 nm; at higher concentrati ons, a new face to face excimer emission appears on longer wavelengths; in the thin film state, the fluorescence emission becomes a single band peakin g at 470 nm. Cyclic voltammetry of DPP and the hole transport material as e vaporated thin films on ITO (indium tin oxide) was compared with that in so lution and was used to determine the energy levels. The electric field stre ngth dependent electroluminescent behavior of DPP was explained according t o the energy levels by a tunneling mechanism, ruling out the possible cause by an excimer or exciplex formation. At a drive voltage of 18 V, the blue electroluminescence reached 2400 ed m(-2).