Blue OLEDs with narrow bandwidth using CF₃ substituted bis((carbazol-9-yl)phenyl)amines as emitters: Structural regulation of linker between donor and acceptor in chromophores

Three new donor-acceptor (D-A) chromophores decorated with bis(trifluoromethyl)-substituted phenyl group as acceptor and bis(4-(9H-carbazol-9-yl)phenyl)amine as donor unit, namely 1,4-naphthyl-CF₃ (1), 1,5-naphthyl-CF₃ (2) and Ph-CF₃ (3), were designed and synthesized. Their photophysical and electrochemical characteristics, and corresponding theoretical calculations were investigated. They showed blue emissions with high photoluminescence quantum yields (PLQY). Doped organic light-emitting diodes (OLEDs) based on them were fabricated, which exhibited strong blue electroluminescence with emission peaks at 453, 446 and 440 nm and full width at half maximum (FWHM) of 69, 65 and 65 nm, respectively. Their Commission International del'Eclairage (CIE) coordinates correspond to (0.169, 0.158), (0.176, 0.134) and (0.163, 0.099). Besides, the maximum current efficiencies (CEs) of 2.8, 5.0 and 4.9 cd A⁻¹; power efficiencies (PEs) of 2.9, 5.4 and 5.2 lm W⁻¹; external quantum efficiencies (EQEs) of 2.3, 2.3 and 3.4% were achieved for 1,4-naphthyl-CF₃ (1), 1,5-naphthyl-CF₃ (2) and Ph-CF₃ (3) doped devices D1, D2 and D3, respectively. This study clearly showed that the optoelectronic properties of these organic small molecules can be regulated by rational design of molecular structures, and their emission wavelengths could be finely tuned within the blue region.