Macromolecules, Vol.40, No.19, 6799-6806, 2007
Increased efficiencies of the copolymers with fluoro groups in vinylene units
New electroluminescent copolymers with fluoro groups in the vinylene unit, poly(9,9-dihex ylfluorene-2,7-vinylene-co-p-phenylenedifluorovinylene) (PFVPDFV), have been synthesized by the GILCH polymerization. The fluoro groups were introduced on vinylene units to increase the electron affinities of the copolymers. The PFVPDFVs exhibit absorption spectra with maximum peaks at 371-413 nm. The maximum absorption peak at 413 nm of PFVPDFV1 was blue-shifted with a larger amount of the PDFV. In the PL spectra of PFVPDFVs, as the PDFV content increases up to 50% in the copolymer system, the fwhm was decreased by 4-38 nm as compared to PFV. The HOMO energy levels of the copolymers were about 5.25-5.50 eV, and the LUMO energy levels were about 2.67-2.97 eV. The polymer LEDs (ITO/PEDOT/polymer/A1) of PFVPDFVs showed emission with maximum peaks at around 472-538 nm. By adjusting the feed ratios of PDFV in the copolymers, it was possible to tune the emission colors from greenish yellow to orange depending on the obtained CIE coordinates. The luminescence efficiencies of the copolymers at room temperature are about 0.1-1.47 cd/A. PFVPDFV3 showed the maximum brightness of 4870 cd/m(2) and the highest luminescence efficiency of 1.47 cd/A. The introduction of up to 50% of PDFV in PFVPDFVS can enhance the device performance to result in high current density, brightness, and efficiency due to the increased electron injection ability caused by the presence of fluoro groups in the vinylene units.