Quenching: A novel water-soluble guanidinium-containing phenylene-ethynylene-based fluorescence sensor (see picture) is reported with a two-fold improvement in sensitivity to electron-deficient quenchers compared to an equivalent alkoxy-substituted phenylene-ethynylene-based sensor. Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

We report a new cationic poly(phenylene ethynylene) (PPE) derivative that exhibits strong amplified fluorescence quenching in the presence of electron-deficient species, yielding high Stern-Volmer coefficients of 4.7 × 10 M in aqueous solutions. Importantly, with the addition of appropriate non-ionic surfactants, the polymer is found to retain its excellent sensitivity even when transferred to high ionic strength buffered media, which have previously been shown to suppress the amplified quenching effect in other polyelectrolyte systems. The cationic PPE derivative yields Stern-Volmer coefficients as high as 10 M in 25 mM buffer solutions of both tris(hydroxymethyl) aminomethane (Tris) and sodium acetate containing 150 mM sodium chloride, the optimal conditions for many enzymes such as phosphatases. The ability to maintain high Stern-Volmer coefficients in high ionic strength buffered media extends the applicability of ionic conjugated polymers to high sensitivity detection in biological media, and thus greatly enhances their versatility as biological sensors.

In this report, we have studied the influence of the nature of the end groups (bromine or hydrogen) of regioregular poly(3-hexylthiophene) (P3HT) polymers on the performance of polymer solar cells made with blend films of P3HT and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C-61 (PCBM). Films and devices were studied before and after annealing at 140 degrees C for 2 h. The effects of the end-group type on the properties of pristine polymers and blend films were examined using optical absorption and emission spectroscopy, transient absorption spectroscopy, and measurements of photovoltaic device performance. It was observed that hydrogen end groups result in slightly higher absorption coefficients, higher photoluminescence intensities, faster and less dispersive charge recombination, and superior solar cell performance (notably a higher fill factor) compared to bromine end groups. The results are attributed to more-ordered polymer-chain packing in blend films made with hydrogen-capped P3HT, on account of the smaller size and weaker electrostatic interactions resulting from hydrogen compared to bromine. Some influence of the C-Br group on exciton quenching may also be present. The effect of the bromine end group on solar-cell performance became more pronounced with reducing incident-light intensity. Comparison of the polymer transport characteristics in organic field-effect transistor configuration indicated that the bromine end group enhances hole trapping.

The charge transport properties of conjugated polymer semiconductors are governed by strong electron phonon coupling, leading to polaron formation as well as the presence of structural and electronic disorder. However, the relative contribution which polaronic relaxation and disorder broadening make to the temperature activation of the mobility of these materials is not well understood. Here we present a combined study of the temperature and concentration dependences of the field-effect mobility and the optically induced electron-transfer transitions of a series of poly(3-hexylthiohene) field-effect transistors of different molecular weight. We apply a vibronic coupling model to extract the reorganization energy and the strength of electronic coupling from the optical spectra. We observe a transition from a localized to a delocalized transport regime as a function of molecular weight and crystalline quality. Polaron activation is comparable to disorder-induced activation in the low-mobility regime [similar to 10(-3) cm(2)/(V s)] and needs to be taken into account when interpreting the field-effect mobility, while disorder becomes the dominant mechanism to limit charge transport in the high-mobility regime with mobilities > 10(-2)-10(-1) cm(2)/(V s).

Until recently, the synthesis of polythiophenes using Suzuki chemistry has proven difficult because of the ready protodeborylation of thiophene boronates. However, we now report that the new generation of bulky, electron-rich Pd(0)-phosphane catalysts are effective and reliable for the preparation of regioregular polyalkylthiophenes using Suzuki coupling. Moreover, the monomers can be prepared in high yield by Ir-catalysed borylation, without the need for strong organolithium bases, making this potentially a highly functional group-tolerant approach to polyalkylthiophene derivatives. Perfluoroalkylthiophenes also undergo this reaction.

We have applied palladium complexes of bulky, electron-rich phosphatic ligands as catalysts for the Suzuki synthesis of highly head-to-tail regioregular polyalkylthiophenes from 2-(5-bromo-4-n-alkyl-thiophen-2-yl)-4,4,5,5-tetramethyl-[1,3,2]dioxaborolane. The monomer can be prepared in high yield by Ir-catalysed borylation of 2-bromo-3-hexylthiophene, without the need for organolithium reagents or strong bases. (c) 2006 Elsevier Ltd. All rights reserved.

Interchain interactions have a profound effect on the optical as well as charge transport properties of conjugated polymer thin films. In contrast to oligomeric model systems in solution-deposited polymer thin films the study of such effects is complicated by the complex microstructure. We present here a detailed study of interchain interaction effects on both charged polarons as well as neutral excitons in highly crystalline, high-mobility poly-3-hexylthiophene (P3HT) as a function of molecular weight. We find experimental evidence for reduced exciton bandwidth and increased polaron delocalization with increasing conjugation length and crystalline quality. From comparative studies of field-effect transistor characteristics, film morphology, and optical properties our study provides a microscopic understanding of the factors which limit the charge transport in P3HT to field-effect mobilities around $0.1\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$, and which will need to be addressed to improve mobility further.

Low-cost photovoltaic energy conversion using conjugated molecular materials has become increasingly feasible through the development of organic ‘bulk heterojunction (BHJ)’ structures 1 , 2 , 3 , 4 , 5 , 6 , 7 , where efficient light-induced charge separation is enabled by a large-area donor–acceptor interface 2 , 3 . The highest efficiencies have been achieved using blends of poly(3-hexylthiophene) (P3HT) and a fullerene derivative 8 , 9 , 10 , 11 , 12 , but performance depends critically on the material properties and processing conditions. This variability is believed to be influenced by the self-organizing properties of P3HT, which means that both optical 13 , 14 and electronic 15 , 16 properties are sensitive to the molecular packing. However, the relationship between molecular nanostructure, optoelectronic properties of the blend material and device performance has not yet been demonstrated. Here we focus on the influence of polymer regioregularity (RR) on the molecular nanostructure, and hence on the resulting material properties and device performance. We find a strong influence of RR on solar-cell performance, which can be attributed to enhanced optical absorption and transport resulting from the organization of P3HT chains and domains. Further optimization of devices using the highest RR material resulted in a power conversion efficiency of 4.4%, even without optimization of electrodes 7 .

The development of p-type semiconducting polymers demonstrating good stability under ambient operation is of importance for the development of low cost, printed electronics. We present here the synthesis and full characterisation of two soluble terthiophene polymers, and examine the effect of introducing a fused aromatic heterocycle, thieno[2,3-b]thiophene, into a terthiophene polymer backbone. This heterocycle contains a cross-conjugated central double bond, and its inclusion was shown to have a marked influence on the optical, thermal and electrical properties of the terthiophene polymer. Transistors were fabricated from both polymers, and the operation and storage lifetime under ambient operation was compared.