Synthesis and electroluminescent properties of poly(p-phenylenevinylene)s with 3′,3′-diheptyl-3,4-propylenedioxythiophene pendant group for light-emitting diode applications

Using the Gilch polymerization method, we synthesized a new series of green electroluminescent polymer, poly[1,4-{2-(3,3'-diheptyl-3,4-propylenedioxythiophen-2-yl)}phenylenevinylene], poly(PDOT-PV), which is a series of fully conjugated poly(p-phenylenevinylene) derivatives with a propylenedioxythiophene (PDOT) moiety as a side-chain. We also synthesized copolymers, poly(PDOT-PV-co-m-SiPhPV), of poly(PDOT-PV) with poly[2-(3-dimethyldodecylsilyphenyl)-1,4-phenylenevinylene], poly(m-SiPhPV), segments. The resulting polymers were highly soluble in common organic solvents and could be easily spin-coated onto an indium-tin oxide coated glass substrate to obtain high quality optical thin films. The weight-average molecular weight (M-w) and polydispersity of poly(PDOT-PV) were 22.0 x 10(4) and 5.3, respectively, and those of poly(PDOT-PV-co-m-SiPhPV) were in the ranges (23.2-36.7) x 10(4) and 5.0-5.8, respectively. The stability of the resulting polymers is adequate for the fabrication of devices, and they provide longevity to devices because they have high glass transition temperatures (T-g). We fabricated polymer light-emitting diodes (PLEDs) in ITO/PEDOT/light-emitting polymer/cathode configurations using either double-layer LiF/Al or triple-layer Alq(3)/LiF/Al cathode structures. For PLEDs containing poly(PDOT-PV) and poly(PDOT-PV-co-m-SiPhPV), the performance was highest using triple-layer cathodes. The turn-on voltages of PDOT-based light-emitting polymers were in the range of 6.0-9.0 V, and the maximum brightness and luminance efficiency were 5127 cd/m(2) at 18 V and 3.75 cd/A at 9 V.