Electromodulation of fluorescence in hole-transporting materials for organic light-emitting diodes. Part II: Starburst amines

Electric field-modulated fluorescence (EMF) spectra were measured in vacuum evaporated films of m-MTDATA (4,4′,4″-tris(N-(3-methylphenyl)-N-phenylamino)triphenylamine) and 1-TNATA (4,4′,4″-tris(N-(1-naphthyl)-N-phenylamino)-triphenylamine), the starburst amines used as hole-transporting materials in organic light-emitting diodes. The external electric field of 106 V/cm strength reduces emission intensity up to 10% in both amines. The exact value of quenching effect depends on excitation photon energy and spectral emission range. The analysis of the experimental data provides evidence that the EMF in starburst amines is due to the field-induced dissociation of excited states into free and/or trapped charge carriers. The 3D-Onsager theory of exciton dissociation explains satisfactorily the observed EMF effect.