No abstract

Two new (dialkylamino)ethoxy-substituted poly(p-phenylene)s (PPP) have been prepared, poly[2,5-bis(3-{N,N-diethylamino}-1-oxapropyl)-1,4-phenylene-alt-1,4-phenylene] (P−NEt2) and poly[2,5-bis(3-{N,N-dimethylamino}-1-oxapropyl)-1,4-phenylene-alt-1,4-phenylene] (P−NMe2). These PPPs were synthesized via Pd-catalyzed Suzuki polymerization and are soluble in organic solvents (THF, chloroform) and dilute aqueous acid. Water-soluble quaternary ammonium functionalized PPPs, poly[2,5-bis(3-{N,N,N-triethylammonium}-1-oxapropyl)-1,4-phenylene-alt-1,4-phenylene] dibromide (P−NEt3 +) and poly[2,5-bis(3-{N,N,N-trimethylammonium}-1-oxapropyl)-1,4-phenylene-alt-1,4-phenylene] dibromide (P−NMe3 +), were easily prepared from the neutral polymers. Number-average molecular weights ranging from 5000 to 19 000 g mol-1 were measured by GPC (relative to PS standards), and these values were standardized to PPP's via universal calibration. The neutral polymer is stable to over 300 °C by TGA, while the alkylated polymers begin to dealkylate at 230 °C. The polymer's electronic absorption is dependent on quaternization with the neutral polymer having a λmax at 350 nm, while the triethyl quaternized polymer's λmax shifts to 330 nm. This corresponds to an electronic band gap (E g) shift from 3.0 to 3.3 eV where E g is defined as the onset of the π to π* transition. The polymers luminesce blue light with an intensity that is a function of ionic composition, allowing them to be used as emitting materials in LED's constructed by both layer-by-layer electrostatic deposition and hybrid ink jet printing methods.

A hybrid inkjet printing (HIJP) technology, which combines a pin-hole free polymer buffer layer and an inkjet printed polymer layer, allows the patterning of high quality polymer light-emitting devices. In this letter, we present a successful demonstration of controllable patterning of dual-color polymer light-emitting pixels using this HIJP technique. In this demonstration, the polymer buffer layer is a wide band gap, blue emitting semiconducting polymer prepared by the spin-casting technique. The inkjet printed layer is a red-orange semiconducting polymer which was printed onto the buffer layer. When a proper solvent was selected, the printed polymer diffused into the buffer layer and efficient energy transfer took place generating a red-orange photoluminescence and electroluminescence from the inkjet printed sites. Based on this principle, blue and orange-red dual-color polymer light-emitting pixels were fabricated on the same substrate. The use of this concept represents an entirely new technology for fabricating polymer multicolor displays with high-resolution, lateral patterning capability.

A water-soluble conjugated polymer was developed that displays significant fluorescence quenching (25% quenching of polymer's fluorescence at quencher concentrations of 500 nM) and forms well-defined multilayer structures via electrostatic deposition. The polymer contains alternating 2,5thienyl-and 2,5-bis[2-(N,N-diethylamine)-1-oxapropyl]-substituted 1,4-phenylene units formed by a Stille reaction protocol. Poly({2,5-bis[2-(N,N-diethylamino)-1-oxapropyl]-1,4-phenylene}-alt-2,5-thienylene) (PPT-NEt 2) was synthesized in 80% yield from 2,5-bis(trimethylstannyl)thiophene and the reactive diiodinated species 2,5-bis(3-[N,N-diethylamino]-1-oxapropyl)-1,4-diiodobenzene. The neutral polymer was soluble in THF, chloroform, and 1 M HCl (aq). A number-average molecular weight of 5300 g mol -1 (ca. 40 rings) was measured by GPC (relative to polystyrene standards). PPT-NEt2 is easily converted to the watersoluble polymer, poly{2,5-bis[2-(N,N,N-triethylammonium)-1-oxapropyl]-1,4-phenylene-alt-2,5-thienylene} dibromide (PPT-NEt3 + ), by quaternization with bromoethane. The polymer's electronic absorption is dependent on quaternization with absorption/emission wavelength maxima (λmax) corresponding to 460/ 519 nm for the neutral polymer and 411/495 nm for the quaternized version in the appropriate solvent. Well-defined, thin multilayer films of PPT-NEt 3 + , alternating with poly(acrylic acid) [PAA] or poly(styrene sulfonic acid)[PSS], were deposited via electrostatic deposition onto indium tin oxide coated glass. Polymer light-emitting diodes prepared from PPT-NEt 3 + /PSS exhibited the best results with a λmax of absorption and emission equal to 450 and 558 nm, respectively, external quantum efficiency of 0.017%, and light output of 110 nW.