Abstract
In this work, we designed and synthesized four bipolar blue-emitting materials with carbazole, imidazole, and biphenyl as donor, acceptor, and p bridge, respectively. The twisted phenylimidazole acceptor leads to a wider band-gap and hence deeper blue emission than the conjugated phenanthrimidazole acceptor. For the substituents on the carbazole donor, the t-butyl group could prevent the intramolecular charge transfer (ICT) process more effectively than the methoxy group. A non-doped deep-blue organic light-emitting diodes (OLED) is obtained with CIE coordinates of (0.159, 0.080), a maximum luminance of 11,364 cd/m2, and a maximum EQE of 4.43%.
Highlights
Density functional theory (DFT) calculation was carried out employing Gaussian 03 at the
The HOMO of BCzB-PPI and BCzB-PIM with t-butyl moiety on the carbazole unit are almost localized on the whole molecule
MoCzB-PPI and MoCzB-PIM with methoxy group, the HOMO is mainly located on the electron-rich carbazole unit
Summary
The transitions from the HOMO to the LUMO + 1 in methoxy substituted compounds (MoCzB-PPI and MoCzB-PIM) are nearly forbidden in the photo-absorption process, owing to their complete separation characters. The relatively large red shift of MoCzB-PPI and MoCzB-PIM with methoxy group in polar solvents is due to their relatively separated HOMO and LUMO.
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