Water-Soluble and Blue Luminescent Cationic Polyelectrolytes Based on Poly(<i>p</i>-phenylene)

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 (Eg) shift from 3.0 to 3.3 eV where Eg 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.