Multicomponent emission from organic light emitting diodes based on polymer dispersion of an aromatic diamine and an oxadiazole derivative

The electroluminescence (EL) spectra of single layer (SL) and double layer (DL) light emitting diodes (LEDs) based on N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′ diamine (TPD) and 2-(4-biphenyl)-5-(4-tert.-butylphenyl)1,3,4-oxadiazole (PBD) molecules incorporated in bisphenol-A–polycarbonate (PC) matrix were investigated. The EL spectra of both SL and DL ((TPD+PC)/PBD) LEDs reveal several components up to four emission bands for DL structure devices. Only the blue band can be ascribed to emission of one of the dopants (TPD), the origin of other red-shifted bands show characteristics suggesting formation of excited hetero-molecular aggregates such as exciplexes and electroplexes including their modification by local energetic conditions.