Novel naphthyridine-based compounds in small molecular non-doped OLEDs: synthesis, properties and their versatile applications for organic light-emitting diodes

Abstract

A series of six new n-type conjugated 1,8-naphthyridine oligomers were examined in organic light emitting diodes (OLEDs). The compounds show a high fluorescence in both solution (10⁻⁸ M) and the solid state. The naphthyridines have high glass-transition (T_g = 65–105 °C) and decomposition (T_d = 380–400 °C) temperatures, reversible electrochemical reduction, and high electron affinities (2.79–3.00 eV). Systematic variation of the spacer linkage can modulate and fine-tune their properties. They emit high blue, green and yellow photoluminescence with 0.70–1.0 quantum yields. Good-performance, single-layer emitter OLEDs with yellow to white-pink emission have also been demonstrated using these materials. White-pink emitter give a performance with a high brightness (400 cd m⁻² at 4 V), and 0.6 cd A⁻¹. Yellow emitters give the best performance with maximum brightness of 250 cd m⁻² with a maximum current efficiency of 1.2 cd A⁻¹. These results demonstrate the potential of this new class of n-type conjugated oligomers as emitters and electron-transport materials for developing high-performance yellow to white-pink OLEDs.