Optical properties of a novel derivative of 2,6-linked quinquepyridine

Both photoluminescence (PL) and electroluminescence (EL) properties of 6,6″″-dimethyl-4′,4″″-diphenyl-2,2′:6′ ,2″:6″,2‴:6‴,2″″-quinquepyridine (DMDPQPY), a derivative of quinquepyridine, were investigated. In as-obtained powder states, its PL spectra show two emission peaks one at 365 nm and another at 556 nm. Similar spectral pattern were obtained in vacuum evaporated film state and in dispersed state in KBr plate. In CHCl₃ solution it emits at 358 nm with a shoulder at 346 nm, whereas in acetic acid, it emits with a single peak at 401 nm. The significant effect of morphology on the relative intensity of the two emissions indicates that the visible emission is an excimer-like one as in the case of previously reported poly(para-pyridine). EL results of typical single layer devices show that the emission maximum in the visible range undergoes a blue shift with the decrease of the DMDPQPY layer thickness. The introduction of a hole transporting layer polyvinylcarbazole in the double layer devices results in significant enhancement of the luminance due to much better balanced charge injection.