Construction and Properties of Octahydrobinaphthol-based Chiral Luminescent Materials with Large Steric Hindrance

Using chiral luminescent material as the emitting core in organic light-emitting diodes (OLEDs) would make these devices possess circularly polarized electroluminescence (CPEL) performance, namely CP-OLEDs, which are of great value for facilitating the development of the next generation of display technologies, especially for implementing real 3D display. In this study, a pair of octahydrobinaphthol (OBN)-based thermally activated delayed fluorescence (TADF) materials, (S/R)-OBN-tBuCz, are developed by ingeniously merging a chiral source (OBN) and a luminophore skeleton (tert-butylcarbazole cyanobenzene). The peripheral sixteen hydrogen atoms in cyclohexane part of OBN unit and the larger tertiary butyl group could effectively increase the steric hindrance of chiral luminescence molecules, reduce the intermolecular stacking effect and inhibit concentration quenching, for effectively improving the luminescence efficiency of the devices. The synthesized chiral luminescent materials exhibit bright green light emission (523 nm), high photoluminescence quantum yield (85.2%), a small Delta E-ST of 0.05 eV with TADF property as well as excellent thermal stability. The chiroptical properties of (S/R)-OBN-tBuCz enantiomers in the ground and excited states are investigated by circular dichroism (CD) and circularly polarized luminescence (CPL) spectra, and the strong symmetrically circularly polarized luminescent signals with gPL of +8.6x10(-4) and -6.5x10(-4) in toluene solution are observed for (S)-OBN-tBuCz and (R)-OBN-tBuCz, respectively, indicating that the chirality is successfully induced into the TADF skeleton through chirality transmitting of OBN unit. Considering the efficient TADF and CPL properties, the enantiomers are employed as chiral emitters for fabricating CP-OLEDs. The electroluminescent devices based on (S/R)-OBN-tBuCz exhibit decent performances with the turn-on voltage of 3.9 V, the maximum brightness of 27709 cd.m(-2), the maximum current efficiency of 43.8 cd.A(-1), the maximum power efficiency of 33.5 lm.W-1, the maximum external quantum efficiency of 12.4% and low efficiency roll-off as well as obvious circularly polarized electroluminescence signals with gEL of +1.57x10(-3) and -0.90x10(-3), respectively. The design strategy of rationally merging chiral source and TADF skeleton can promote the development of chiral luminescent materials and circularly polarized electroluminescent devices.