High brightness circularly polarized electroluminescence from conjugated polymer F8BT induced by chiral binaphthyl-pyrene

Abstract

Chiral organic polymers have considerable potential in solution-processable circularly polarized organic light emitting diodes (CP-OLEDs) due to their simple, low cost and large-area processing. Achiral conjugated poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]-thiadiazol-4,8-diyl)] (F8BT) is a donor–acceptor copolymer with superior characteristics including its ability to uniformly disperse chiral dopants and form homogeneous and smooth films. This paper describes the design and development of blue-emission chiral enantiomers R-/S-3 bearing pyrene groups as fluorophores and 2,2′-methylenedioxy-1,1′-binaphthalene moieties as chiral sources. Enantiomers R-/S-3 exhibit high thermal properties, outstanding photoluminescence properties and sufficient solubility in common organic reagents. The CP-OLEDs using R-/S-3 as the blue emission emitting layer show excellent efficiency, high brightness, and low turn-on voltage in non-doped OLEDs. Moreover, we further employed achiral conjugated fluorescent polymer F8BT, blended with blue-emitting chiral dopants (R-/S-3), as the device emitting layer. The CP-OLEDs based on blends of F8BT + 10% R-/S-3 showed low turn-on voltage (V_on = 4.1 V), excellent current efficiencies (4.19 cd A⁻¹ for F8BT + 10% R-3 and 4.06 cd A⁻¹ for F8BT + 10% S-3), and high brightness (21797.8 cd m⁻² for F8BT + 10% R-3 and 20572.6 cd m⁻² for F8BT + 10% S-3). To our knowledge, this is, to date, the best device performance using blends of achiral fluorescent polymers and chiral inducers in solution-processable CP-PLEDs. The outcomes obtained in this study can provide us with a valuable reference for future studies on the induced CPL-active device design.