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.

The discovery that conjugated polymers can be utilized as efficient emitters in thin-film electroluminescent devices has created a flurry of research effort over the past few years. [1] Current efforts have produced devices with high quantum efficiencies (1±4 %) and brightness, respectable lifetimes, and the full spectrum of colors, including white light. [2] While poly(phenylenevinylene) (PPV) and its derivatives are the most well-studied conjugated polymers for use in light-emitting devices; poly(p-phenylene) (PPP) based molecules have also received attention as emitting materials. [3±9] Due to its large bandgap, PPP has the desired quality of emitting in the blue region of the spectrum, which is not easily achieved with other conjugated polymers. However, because of the poor processibility of PPP in its underivatized form, previous workers have synthesized PPP ladder±type polymers with chemical bridging units between phenylene rings [10] as well as ring-functionalized PPPs [11] to promote solubility. The planar laddertype structures often have to be carefully manipulated to avoid the formation of molecular aggregates, which can lead to a red-shifted component of the photoluminescence. [12] Recently, one of us synthesized polyanionic and polycationic versions of PPP that are soluble in water, do not contain bridging units, and do not red-shift from their blue photoluminescence. [13±15] Because of their charged nature and related water solubility, these molecules also have the added advantage that they can be processed at the molecular level by the extremely versatile layer-by-layer sequential adsorption technique.The layer-by-layer sequential adsorption technique has been shown to produce uniform thin films with molecularlevel thickness control. [16] This technique is based on the alternating adsorption of a positively charged molecule and a negatively charged molecule to form a bilayer building block. By repeating this adsorption cycle, a film can be made with a thickness that is determined by the thickness of the individual bilayers (typically 10±60 for polyelectrolytes) and the total number of bilayers adsorbed. Furthermore, by adjusting simple solution parameters such as the amount of added salt [17,18] and the solution pH, [19] the thickness, composition and layer interpenetration of the bilayer building block can be systematically varied. Because of the technique's flexibility and ease of use, multilayer sequential adsorption has been successfully carried out with a variety of charged molecules, both organic and inorganic. [20] Within our research group, the ability to readily construct complex multilayer heterostructures and control electrode interfaces via the sequential adsorption technique, has been exploited with films containing PPV to both optimize and understand the operation of light-emitting thin-film devices. [21,22] More recent work has focused on an optimization of the device performance of PPV and polymeric tris(bipyridyl) ruthenium(II)±containing multilayers through manipulation...

A new class of main chain polypseudorotaxanes, 8, was prepared by self-assembly of a poly(ester crown ether), poly[bis(5-methylene-1,3-phenylene)-32-crown-10 sebacate] (5), and N,N‘-bis(β-hydroxyethyl)-4,4‘-bipyridinium bis(hexafluorophosphate) (6). The equilibrium constant (K = 58.0 M-1 at 21.8 °C), ΔH (−26.5 kJ/mol) and ΔS (−56.4 J/mol deg)(all averages from several iterative methods) for the formation of 8 were measured by proton NMR spectroscopy. Compared to those (K = 247 M-1 at 21.8 °C, ΔH = −44.7 kJ/mol, ΔS = −106 J/mol deg) for the model system, bis(5-acetoxymethyl-m-phenylene)-32-crown-10 (4) and 6, the enthalpy term is less favorable for the polymeric system, while the entropy term is less unfavorable. The measured values enabled us to design polypseudorotaxanes with targeted degrees of threading (m/n, the fraction of the cyclic moieties threaded with linear species). The solubility of polypseudorotaxane 8 was different from both starting materials 5 and 6, and depended on the m/n value. Polypseudorotaxanes 8 with higher m/n had higher viscosities because of increased hydrodynamic volume in solution and were more rigid as manifested by higher glass transition temperatures (T g) in the solid state. Dethreading (decomplexation) took place above T g in the solid state, causing loss of color (orange), a process potentially useful for temperature sensors.

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A series of polyphenylene derivative polymers with a variety of heterocyclic units along the main chain, and various pendant groups, have been synthesized and their optoelectrochemical properties examined. Polyphenylenes containing electronically isolated emitter centers have optical absorption and luminescence characteristics which are a function of the length of the conjugated unit. A water soluble electroactive rigid-rod poly (p-phenylene), specifically Poly[2,5-bis (propoxy-3-sulfonate)-1,4-phenylene-alt,4-phenylene], has been prepared. Solution cast films of this polymer exhibit optical evidence for bipolarons via both p-type and n-type electrochemical doping. Further poly (p-phenylene) (PPP) derivatives are being pursued, including PPP's bearing pendant donor molecules for charge transfer complex formation. A series of polymers containing alternating p-phenylene units with bithienylene and bifuranylene units, specifically poly[1,4-bis (2-heterocycle)-2,5-disubstituted-1,4-phenylenes], have been synthesized with both alkyl and alkoxy pendant groups. Steric interactions disrupt the ability of the redox doped polymers to attain planarity, strongly affecting the polymer's oxidation potentials and DC conductivities. The substituent length has little effect on the electronic properties of the polymer, but greatly affects the polymer's solubility and transport properties during redox switching.