Use of oxazole-based chromophores as neat films in OLED structures: towards efficient deep-blue emitters

Abstract

Numerous oxazole-based fluorophores show efficient emission in the UV and deep blue spectral range in the solid state, making them interesting candidates for use as emissive layers in organic light-emitting diodes (OLEDs). Three ozazole derivatives, i.e. 2-(p-tert-butylphenyl)benzoxazole (Bzx), 2-phenyl-naphthoxazole (Nzx) and 2,2’-di(p-tert-butylphenyl)- 6,6’-bibenzoxazole (BBzx), were used in OLEDs with neat films configurations. These molecules differ by their planarity, steric hindrance and size of the π-conjugated system. No photoluminescence was observed with Bzx and Nzx. In contrast, the incorporation of the bis-chromophore BBzx within thin solid films led to efficient emission. The corresponding OLEDs displayed a deep blue emission at 430 nm arising from the BBzx layer, with CIE coordinate of (0.157, 0.044). These specific optical features were attributed to the twisted molecular structure of the bis-chromophore, leading to reduction of the aggregation induced fluorescence quenching. An EQE of 1.2% was achieved with a driving current of 24 A/m2. The results suggest that BBzx derivatives may be useful as efficient color saturation deep-blue emitters in OLEDs.