Transport and luminescence in naphthyl phenylamine model compounds

Abstract

The effects of polar side groups (methoxy, fluoro, and chloro substitution) on the transport and luminescence properties of a series of naphthyl phenylamine (NPA) compounds were examined. The compounds are (i) N,N′-diphenyl-1-naphthylamine, (ii) N-(4-methoxyphenyl),N′-phenyl-1-naphthylamine, (iii) N-(4-chlorophenyl),N′-phenyl-1-naphthylamine, and (iv) N-(4-fluorophenyl),N′-phenyl-1-naphthylamine. Time-of-flight measurements were used to measure the hole mobilities of the NPA compounds. The hole mobilities were found to correlate with the dipole moments of the compounds. The least polar compound N,N′-diphenyl-1-naphthylamine has the highest mobility in the range of 0.5–2×10−4cm2V−1s−1, whereas the most polar compound N-(4-chlorophenyl),N′-phenyl-1-naphthylamine has the lowest mobility in the range of 0.2–2×10−6cm2V−1s−1 at room temperature. The dipolar disorder model proposed by Dieckmann and Young is found to be applicable to describe the data. The NPA compounds were further incorporated into a multilayer organic light-emitting diode (OLED) as the light-emitting layer. The OLEDs emit in the range 420–440nm, and the polar side groups appear to have no clear influence on the emission wavelength of the molecules in solid state.