Paracyclophane-based bipolar near-ultraviolet emitters showing advanced circularly polarized luminescent properties
Yuling Sun, Hongyan Wang, Siqi Liu, Xinyue Lu, Feng Zhao, Daokun Zhong, Dongming Jia, Xiaolong Yang, Bochao Su, Yuanhui Sun, Jiao Bo, Guijiang Zhou
Abstract
<p>As linking unit, [2.2]paracyclophane (PCP) has been inserted in between electron-donating groups (<i>i.e.</i> carbazole and 10<i>H</i>-phenoxazine) and electron-accepting groups (<i>i.e.</i> triphenyl-1,3,5-triazine and diphenylsulfone) to prepare a series of linear bipolar racemic near-ultraviolet (NUV) emitters owing to the planar chirality associated with the PCP. In toluene, the racemic bipolar PCP-based emitters can show emission wavelength in the range of 400-444 nm. Critically, very small Commission Internationale de L’Eclairage (CIE) chromaticity coordinate of y value of 0.03 has been achieved for the photoluminescent spectra of these bipolar racemic NUV emitters in solution. The PCP-based bipolar emitters can show efficient NUV emission with photoluminescent quantum yields (PLQY) of <i>ca.</i> 0.5 in doped mCP film. In addition, the enantiomers of the NUV emitters have been obtained to show obvious circular dichroism (CD) behavior and circularly polarized luminescence (CPL). The absorption asymmetric factor (<i>g</i><sub>abs</sub>) of <i>ca.</i> 4.4×10<sup>-4</sup> and photoluminescent asymmetric factor (<i>g</i><sub>PL</sub>) of <i>ca.</i> 1.5×10<sup>-3</sup> can be achieved by the PCP-based NUV enantiomers. After doped in the emission layer of organic light-emitting diodes (OLEDs), efficient NUV and deep blue-emitting OLEDs have been constructed. The NUV OLEDs based on the racemic emitters can achieve forward-viewing maximum external quantum efficiency (<i>η</i><sub>ext</sub>) of 5.03% and electroluminescence (EL) peak at 404 nm with CIE<sub>y</sub> of 0.05, while the OLEDs with deep blue emission can show <i>η</i><sub>ext</sub> of 4.12% and EL peak at 412 nm with CIE<sub>y</sub> of 0.08. Furthermore, the NUV chiral enantiomers can bring <i>η</i><sub>ext</sub> of 5.25% and EL peak at 404 nm with CIE<sub>y</sub> of 0.05, while the deep blue chiral enantiomers can give <i>η</i><sub>ext</sub> of 4.40% and EL peak at 412 nm with CIE<sub>y</sub> of 0.08. Clearly, these encouraging EL data show the great potential of these linear PCP-based bipolar emitters in the field of OLEDs.</p>