A series of poly(arylene ethynylene) (PAE) conjugated polyelectrolytes (CPEs) have been prepared using palladium-mediated (Sonogashira) coupling chemistry. The series consists of five pairs of polymers that share the same poly(arylene ethynylene) backbone. One member of each pair contains anionic sulfonate (R−SO3 -) side groups, whereas the other member contains cationic bis-alkylammonium (R-N+−R-N+−R) side groups. The repeat unit structure of the poly(arylene ethynylene) backbone consists of a bis(alkoxy)phenylene-1,4-ethynylene unit alternating with a second arylene ethynylene moiety, and five different arylenes were used, Ar = 1,4-phenyl, 2,5-pyridyl (Py), 2,5-thienyl (Th), 2,5-(3,4-ethylenedioxy)thienyl (EDOT), and 1,4-benzo[2,1,3]thiodiazole (BDT). The different arylene units induce variation in the HOMO−LUMO band gap across the series of polymers, resulting in a series of materials that display absorption maxima at wavelengths ranging from 400 to 550 nm and fluorescence maxima ranging from 440 to 600 nm. The absorption and fluorescence properties of the CPEs were investigated in methanol, water, and in methanol/water mixtures. The photophysical data suggest that the CPE chains aggregate in water, but in methanol, the polymers are well solvated such that the optical properties are characteristic of the “molecularly dissolved” chains. Stern−Volmer (SV) fluorescence quenching studies were carried out using ionic naphthalene diimides as electron acceptors. The results show that the fluorescence from the CPEs was quenched with very high efficiency (amplified quenching) when the ionic diimide was charged opposite to the charge on the CPE chain. The sensitivity of the Stern−Volmer quenching response varies strongly across the series of CPEs, with the most efficient quenching seen for polymers that display efficient fluorescence when they are aggregated. The relationship between CPE side chain structure, band gap, fluorescence quantum yield, extent of chain aggregation, and fluorescence quenching efficiency is discussed.

We describe the layer-by-layer (LBL) fabrication of multilayer films and photovoltaic cells using poly(phenylene ethynylene)-based anionic conjugated polyelectrolytes as electron donors and water-soluble cationic fullerene C60 derivatives as acceptors. LBL film deposition was found to be linearly related to the number of bilayers as monitored by UV-vis absorption. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) of the multilayer films revealed an aggregated but relatively uniform morphology devoid of any long-range phase separation. The maximum incident monochromatic photon to current conversion efficiency (IPCE) of the photovoltaic cells was 5.5%, the highest efficiency reported to date for cells fabricated by using the LBL fabrication technique, and since the thin film cells do not provide complete absorption of the incident light, the current generation per photon absorbed may be as much as 10%. The cells exhibited open circuit voltages of 200-250 mV with highest measured short circuit currents up to 0.5 mA/cm2 and fill factors around 30%. The power conversion efficiencies measured at AM 1.5 solar conditions (100 mW/cm2) varied between 0.01 and 0.04%, and similar to the IPCE results, the efficiency is a function of the thickness of the PV active layer.

The spectral broadening concept is demonstrated through use of a dual conjugated polyelectrolyte (CPE) system to enhance the performance of polymer-sensitized nanocrystalline TiO2 solar cells. The individual polymer-sensitized cells show relatively similar power conversion efficiencies (η), whereas the coadsorbed, dual polymer cells more than doubled the η value.

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The photoluminescent and electroluminescent properties of near-infrared (near-IR) emitting lanthanide monoporphyrinate complexes, Ln(TPP)L (L ) hydridotris(1-pyrazolyl)borate (Tp) or (cyclopentadienyl)tris(diethylphosphinito)cobaltate(I) L(OEt)) blended into conjugated and nonconjugated polymer hosts were characterized. A blue-emitting alkoxysubstituted poly(p-phenylene) (PPP-OR11) was used as the conjugated polymer host and nonconjugated hosts included polystyrene, poly(methyl methacrylate), poly(n-butyl methacrylate), and poly(bisphenol A-carbonate). Complete quenching of the PPP-OR11 host fluorescence (i.e., > 95%) is observed at 5 mol % of Ln(TPP)Tp, and host quenching is accompanied by sensitization of near-IR emission from the lanthanide complex. The photoluminescence results suggest that energy transfer occurs from PPP-OR11 to Ln(TPP)L, presumably via the Fo ¨rster mechanism. Near-IR light emitting diodes (PLEDs) consisting of Yb(TPP)Tp blended into PPP-OR11 and the nonconjugated polymer hosts were characterized. PLEDs fabricated with PPP-OR11 exhibited turn-on voltages of approximately 4 V, whereas nonconjugated polymer devices had higher turn-on voltages (ca. 8 V), independent of the polymer used. Comparable external electroluminescence (EL) efficiencies on the order of 10 -4 were observed from both the conjugated and nonconjugated polymer host devices. Taken together, the available evidence suggests that the dominant mechanism operating in the EL devices involves the Ln(TPP)L complex as the charge-transport material, the center for electron-hole recombination, and the emitter.