Water-Soluble and Blue Luminescent Cationic Polyelectrolytes Based on Poly(p-phenylene)

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−NEt 2 ) and poly[2,5-bis(3-{ N,N -dimethylamino}-1-oxapropyl)-1,4-phenylene- alt -1,4-phenylene] (P−NMe 2 ). 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−NEt 3 + ) and poly[2,5-bis(3-{ N,N,N -trimethylammonium}-1-oxapropyl)-1,4-phenylene- alt -1,4-phenylene] dibromide (P−NMe 3 + ), 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 λ max at 350 nm, while the triethyl quaternized polymer's λ max 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.