Paracyclophane-based bipolar near-ultraviolet emitters showing advanced circularly polarized luminescent properties

Abstract

<p>As linking unit, [2.2]paracyclophane (PCP) has been inserted in between electron-donating groups (<em>i.e.</em> carbazole and 10<em>H</em>-phenoxazine) and electron-accepting groups (<em>i.e.</em> 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 <em>ca.</em> 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 (<em>g</em>_abs) of <em>ca.</em> 4.4��10^-4 and photoluminescent asymmetric factor (<em>g</em>_PL) of <em>ca.</em> 1.5��10^-3 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 (<em>��</em>_ext) of 5.03% and electroluminescence (EL) peak at 404 nm with CIE_y of 0.05, while the OLEDs with deep blue emission can show <em>��</em>_ext of 4.12% and EL peak at 412 nm with CIE_y of 0.08. Furthermore, the NUV chiral enantiomers can bring <em>��</em>_ext of 5.25% and EL peak at 404 nm with CIE_y of 0.05, while the deep blue chiral enantiomers can give <em>��</em>_ext of 4.40% and EL peak at 412 nm with CIE_y 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>