A novel rigid-rod alternating poly(p-phenylenevinylene) derivative with oligo(ethylene oxide) side chains

A novel yellow-green light-emitting rigid-rod copolymer, poly[(2,5-bis(triethoxy)-1,4-phenylenevinylene)-alt-(1,4-phenylen evinylene)] (BTEOPPV-alt-PPV) with an alternating structure containing oligo(ethylene oxide) side chains was synthesized by the Wittig reaction of the corresponding triphenylphosphonium chloride and dialdehyde compounds. This soluble and processable copolymer with both electronic and ionic conduction showed good thermal stability as weight loss was less than 5% on heating to about 365°C under nitrogen atmosphere. The DSC thermogram and other relevant measurements showed the liquid crystalline properties and self-ordering in the copolymer. BTEOPPV-alt-PPV complexed with metal ions shows an ionochromic effect in the absorption spectrum and also in the electroluminescence spectrum due to the covalent linkage of the oligoethyleneoxy side chains as molecular recognition sites to the PPV backbone, which represents an approach toward chemical sensors. The single-layer light-emitting diode (LED) (ITO/polymer/Al) exhibits an emission maximum at ca 552 nm corresponding to yellow-green emission with a turn-on voltage of 7.5 V and efficiency of 0.038 lm/W (120 cd/m², 10 V, 0.1 A/cm²) while the light-emitting electrochemical cell (LEC) (ITO/polymer + LiOTf/Al) without any extra supporting polymer electrolytes for ionic conduction shows a lower turn-on voltage of 2.5 V, enhanced efficiency of 0.185 lm/W (210 cd/m², 4 V, 0.09 A/cm²) and low response times in the submillisecond range.