Controllable Circularly Polarized Electroluminescence Performance Improved by the Dihedral Angle of Chiral-Bridged Binaphthyl-Type Dopant Inducers.

Abstract

Chirality of 1,1'-binaphthol (BINOL) is due to the restricted rotation between two naphthalene rings, and its skeletal structure of binaphthyl unit can be further modified by choosing functionalized substituents to afford the enlarged chiral induction effect. In this paper, we designed and synthesized nine chiral binaphthyl derivatives (R/S-1-R/S-9) as circularly polarized electroluminescence (CP-EL) inducers by inserting various bridged alkyl chains into the hydroxyl groups of BINOL or introducing functionalized substituents with different steric hindrances on the 3,3'-position of 2,2'-methylenedioxy-1,1'-binaphthalene. Their molecular conformations and CPL behaviors of nine chiral inducers were significantly dependent on the length of the alkyl chain and the degree of substituent steric hindrance, which could further regulate their chiral induction effect on achiral fluorescent polymer F8BT from small to large in the doped films. Moreover, in virtue of the planar rigid conjugated molecular conformation of R/S-1, R/S-6, and R/S-9, the amplified CPL signals (|gPL|) were detected as high as 2.36 × 10-2, 2.06 × 10-2, and 1.26 × 10-2 from blends of F8BT and these chiral inducers. The circularly polarized organic light-emitting diode (CP-OLED) device on the blends of F8BT and chiral inducers (R/S-6) with small dihedron angle and excellent carrier mobility showed a low turn-on voltage (Von < 4.5 V), high brightness (> 10509.6 cd/m2), and maximum |gEL| value of 1.86 × 10-2 (F8BT + 5% R/S-6). This work can develop and provide a valuable reference for CP-OLED device design through chiral dopant induction.