Luminescence properties of structurally modified PPVs: PPV derivatives bearing 2-(4-tert-butylphenyl)-5-phenyl-1,3,4-oxadiazole pendants

Two new poly(p -phenylenevinylene) (PPV) derivatives bearing 2-phenyl-5 -(4 -tert-butylphenyl)-1,3,4-oxadiazole pendants were prepared, and their photo - and electroluminescence properties were studied. The first polymer (P-1) is poly[2-(4- [5-(4-tert-butylphenyl)- 1,3,4oxadiazoly]phenyl]-1,4-phenylen evinylen,which is a PPV derivative having diphenyl-substituted 1,3,4-oxadia zole pendant that is known to be an excellent electron-transporting structu re. The second polymer (P-2) is poly[2-(4- [5-(4-tert-butylphenyl)-1,3,4-ox adiazoly phenyl)-5-(2-ethylhexyloxy)-1,4-phenylene]. The only structural di fference between P-l and P-2 is the presence of additional 2-ethylhexyloxy pendant groups in P-2. Both polymers were prepared by direct polymerization of the a,alpha,alpha ' -dibromo-p-xylene monomers having the pendant group (s) in the presence of excess potassium tert-butoxide. Both polymers reveal much improved electroluminescence (EL) properties when compared with PPV. They emit luminescence light over the wavelength range from about 500 to 60 0 nm. The external quantum efficiencies of P-l and P-2 were respectively 16 and 56 times the value for PPV when LED devices were fabricated using an i ndium-tin oxide (ITO) coated glass anode and the aluminum cathode. In parti cular, the EL device ITO/poly(3,4-ethylenedioxy-2,4-thienylene)/P-2/Al:Li g eometry revealed a maximum luminance of 1090 cd/m(2) at the electric field of 2.36 MV/cm with the external quantum efficiency of 0.045%. The maximum b rightness of the ITO/P-2/Ca/Al was 7570 cd/m(2) at the electric field of 2. 80 MV/cm.