Properties of a new pyrazoline derivative and its application in electroluminescence

Abstract

As evaporated thin film and in solution, the absorption spectra, photoluminescence, 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 concentrations, the fluorescence emission is at 415 nm; at higher concentrations, a new face to face excimer emission appears on longer wavelengths; in the thin film state, the fluorescence emission becomes a single band peaking at 470 nm. Cyclic voltammetry of DPP and the hole transport material as evaporated thin films on ITO (indium tin oxide) was compared with that in solution and was used to determine the energy levels. The electric field strength dependent electroluminescent behavior of DPP was explained according to 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 cd m ^–2 .