Poly(p-phenylenevinylene)s Derivatives Containing a New Electron-Withdrawing CF₃F₄Phenyl Group for LEDs

Abstract

New PPV derivatives which contain electron-withdrawing CF 3 F 4 phenyl group, poly[2-(2-ethylhexyloxy)-5-(2,3,5,6-tetrafluoro-4-trifluoromethylphenyl)-1,4-phenylenevinylene] (CF 3 F 4 P-PPV), and poly[2-(4-(2-etylhexyloxy)-phenyl)-5-(2,3,5,6-tetrafluoro-4-trifluoromethylphenyl)-1,4-phenylenevinylene] (P-CF 3 F 4 P-PPV), have been synthesized by GILCH polymerization. As the result of the introduction of the electron-withdrawing CF 3 F 4 phenyl group to the phenyl backbone, the LUMO and HOMO energy levels of CF 3 F 4 P-PPV (3.14, 5.50 eV) and P-CF 3 F 4 P-PPV (3.07, 5.60 eV) were reduced. The PL emission spectra in solid thin film are more redshifted over 50 nm and increased fwhm (full width at half maximum) than solution conditions by raising aggregation among polymer backbone due to electron withdrawing effect of 2,3,5,6-tetrafluoro-4-trifluoromethylphenyl group. The EL emission maxima of CF 3 F 4 P-PPV and P-CF 3 F 4 P-PPV appear at around 530-543 nm. The current density-voltage-luminescence (J-V-L) characteristics of ITO/PEDOT/polymer/Al devices of CF 3 F 4 P-PPV and P-CF 3 F 4 P-PPV show that turn-on voltages are around 12.5 and 7.0 V, and the maximum brightness are about 82 and 598 cd/m 2 , respectively. The maximum EL efficiency of P-CF 3 F 4 P-PPV (0.51 cd/A) was higher than that of CF 3 F 4 P-PPV (0.025 cd/A).