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

As linking unit, [2.2]paracyclophane (PCP) has been inserted in between electron-donating groups (i.e. carbazole and 10H-phenoxazine) and electron-accepting groups (i.e. 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 ca. 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 (g_abs) of ca. 4.4×10^-4 and photoluminescent asymmetric factor (g_PL) of ca. 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 (η_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 η_ext of 4.12% and EL peak at 412 nm with CIE_y of 0.08. Furthermore, the NUV chiral enantiomers can bring η_ext of 5.25% and EL peak at 404 nm with CIE_y of 0.05, while the deep blue chiral enantiomers can give η_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.