Hexyl‐Substituted Oligoselenophenes with Central Tetrafluorophenylene Units: Synthesis,Characterisation and Application in Organic Field Effect Transistors

A series of selenophene oligomers incorporating conjugated fluorinated phenylene units have been synthesised as potential semiconductor materials for organic field‐effect transistors (OFETs). X‐ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, making them ideal candidates for OFET applications.

     

Enhancements in travelling wave ion mobility resolution

The use of ion mobility separation to determine the collision cross-section of a gas-phase ion can provide valuable structural information. The introduction of travelling-wave ion mobility within a quadrupole/time-of-flight mass spectrometer has afforded routine collision cross-section measurements to be performed on a range of ionic species differing in gas-phase size/structure and molecular weight at physiologically relevant concentrations. Herein we discuss the technical advances in the second-generation travelling-wave ion mobility separator, which result in up to a four-fold increase in mobility resolution. This improvement is demonstrated using two reverse peptides (mw 490 Da), small ruthenium-containing anticancer drugs (mw 427 Da), a cisplatin-modified protein (mw 8776 Da) and the noncovalent tetradecameric chaperone complex GroEL (mw 802 kDa). What is also shown are that the collision cross-sections determined using the second-generation mobility separator correlate well with the previous generation and theoretically derived values.     

Charge carrier formation in polythiophene/fullerene blend films studied by transient absorption spectroscopy

We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt % 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C61 (PCBM). Three polymers are observed to give amorphous films, attributed to a nonplanar geometry of their backbone while the other five polymers, including poly(3-hexylthiophene), give more crystalline films. Optical excitation of the pristine films of the amorphous polymers is observed by transient absorption spectroscopy to give rise to polymer triplet formation. For the more crystalline pristine polymers, no triplet formation is observed, but rather a short-lived (approximately 100 ns), broad photoinduced absorption feature assigned to polymer polarons. For all polymers, the addition of 5 wt % PCBM resulted in 70-90% quenching of polymer photoluminescence (PL), indicative of efficient quenching of polythiophene excitons. Remarkably, despite this efficient exciton quenching, the yield of dissociated polymer+ and PCBM- polarons, assayed by the appearance of a long-lived, power-law decay phase assigned to bimolecular recombination of these polarons, was observed to vary by over 2 orders of magnitude depending upon the polymer employed. In addition to this power-law decay phase, the blend films exhibited short-lived decays assigned, for the amorphous polymers, to neutral triplet states generated by geminate recombination of bound radical pairs and, for the more crystalline polymers, to the direct observation of the geminate recombination of these bound radical pairs to ground. These observations are discussed in terms of a two-step kinetic model for charge generation in polythiophene/PCBM blend films analogous to that reported to explain the observation of exciplex-like emission in poly(p-phenylenevinylene)-based blend films. Remarkably, we find an excellent correlation between the free energy difference for charge separation (deltaG(CS)rel) and yield of the long-lived charge generation, with efficient charge generation requiring a much larger deltaG(CS)rel than that required to achieve efficient PL quenching. We suggest that this observation is consistent with a model where the excess thermal energy of the initially formed polaron pairs is necessary to overcome their Coulombic binding energy. This observation has important implications for synthetic strategies to optimize organic solar cell performance, as it implies that, at least devices based on polythiophene/PCBM blend films, a large deltaG(CS)rel (or LUMO level offset) is required to achieve efficient charge dissociation.     

Synthesis, structural and spectroscopic characterisation of three di-μ-fluoro-bis[dioxouranyl] complexes

Three novel uranyl complexes with organic phosphine oxide ligands and bridging fluorides have been synthesised and structurally characterised. In [ UO₂(μ-F)(TPPO)_{3 2}][BF₄]₂ · ⁿC₆H₁₄, 1, and [ UO₂(-μF)(TBPO)_{3 2}][BF₄]₂ 2, (where TPPO and TBPO are triphenylphosphine oxide and tri-n-butylphosphine oxide, respectively) two UO₂ ²⁺ moieties are bridged by two fluorides with three additional terminal PO donor ligands coordinated to each uranium centre. The dicationic complexes are both charge balanced by two uncoordinated tetrafluoroborate anions. In the related structure, [UO₂(μ-F)(F)(DPPMO₂)]₂ · 2MeOH (3), terminal fluoride is also coordinated to both uranyl centres (where DPPMO₂ = bis(diphenylphosphine oxide)methane). All three complexes were prepared during attempted syntheses of complexes with tetrafluoroborate directly coordinated to uranium. It is clear from these results that the fluorophilicity of UO₂ ²⁺ causes the abstraction of fluoride from [BF₄]⁻, with the weakly coordinating anion only present as a counter cation in 1 and 2, and absent completely in 3.     

Enantioselective synthesis of bicyclo[3.n.1]alkanes by chiral phosphoric acid-catalyzed desymmetrizing Michael cyclizations

2,2-Disubstituted cyclic 1,3-diketones containing a tethered electron-deficient alkene undergo chiral phosphoric acid-catalyzed desymmetrizing Michael cyclizations to give bridged bicyclic products in high enantioselectivities. Both bicyclo[3.2.1]octanes and bicyclo[3.3.1]nonanes are accessible using this methodology.     

Validation of an assay for the determination of levoglucosan and associated monosaccharide anhydrides for the quantification of wood smoke in atmospheric aerosol

Biomass burning is becoming an increasing contributor to atmospheric particulate matter, and concern is increasing over the detrimental health effects of inhaling such particles. Levoglucosan and related monosaccharide anhydrides (MAs) can be used as tracers of the contribution of wood burning to total particulate matter. An improved gas chromatography–mass spectrometry method to quantify atmospheric levels of MAs has been developed and, for the first-time, fully validated. The method uses an optimised, low-volume methanol extraction, derivitisation by trimethylsilylation and analysis with high-throughput gas chromatography–mass spectrometry (GC–MS). Recovery of approximately 90 % for levoglucosan, and 70 % for the isomers galactosan and mannosan, was achieved using spiked blank filters estimates. The method was extensively validated to ensure that the precision of the method over five experimental replicates on five repeat experimental occasions was within 15 % for low, mid and high concentrations and accuracy between 85 and 115 %. The lower limit of quantification (LLOQ) was 0.21 and 1.05 ng m^?3 for levoglucosan and galactosan/mannosan, respectively, where the assay satisfied precisions of ≤20 % and accuracies 80–120 %. The limit of detection (LOD) for all analytes was 0.105 ng m^?3. The stability of the MAs, once deposited on aerosol filters, was high over the short term (4 weeks) at room temperature and over longer periods (3 months) when stored at ?20 °C. The method was applied to determine atmospheric levels of MAs at an urban background site in Leicester (UK) for a month. Mean concentrations of levoglucosan over the month of May were 21.4?±?18.3 ng m^?3, 7.5?±?6.1 ng m^?3 mannosan and 1.8?±?1.3 ng m^?3 galactosan. Figure

Monosaccharide anhydride levels and percent contribution to PM₁₀ from filter punches taken every 24 h at an urban background site in Leicester, analysed by GC–MS. G galactosan, M mannosan, L levoglucosan     

Kinetics of aquation and anation of ruthenium(II) arene anticancer complexes, acidity and X-ray structures of aqua adducts

The aqua adducts of the anticancer complexes [(eta(6)-X)Ru(en)Cl][PF(6)] (X=biphenyl (Bip) 1, X=5,8,9,10-tetrahydroanthracene (THA) 2, X=9,10-dihydroanthracene (DHA) 3; en=ethylenediamime) were separated by HPLC and characterised by mass spectrometry as the products of hydrolysis in water. The X-ray structures of the aqua complexes [(eta(6)-X)Ru(en)Y][PF(6)](n), X=Bip, Y=0.5 H(2)O/0.5 OH, n=1.5 (4), X=THA, Y=0.5 H(2)O/0.5 OH, n=1.5 (5 A), X=THA, Y=H(2)O, n=2 (5 B), and X=DHA, Y=H(2)O, n=2 (6), are reported. In complex 4 there is a large propeller twist of 45 degrees of the pendant phenyl ring with respect to the coordinated phenyl ring. Although the THA ligand in 5 A and 5 B is relatively flat, the DHA ring system in 6 is markedly bent (hinge bend ca. 35 degrees ) as in the chloro complex 3 (41 degrees ). The rates of aquation of 1-3 determined by UV/Vis spectroscopy at various ionic strengths and temperatures (1.23-2.59x10(-3) s(-1) at 298 K, I=0.1 M) are >20x faster than that of cisplatin. The reverse, anation reactions were very rapid on addition of 100 mM NaCl (a similar concentration to that in blood plasma). The aquation and anation reactions were about two times faster for the DHA and THA complexes compared to the biphenyl complex. The hydrolysis reactions appear to occur by an associative pathway. The pK(a) values of the aqua adducts were determined by (1)H NMR spectroscopy as 7.71 for 4, 8.01 for 5 and 7.89 for 6. At physiologically-relevant concentrations (0.5-5 microM) and temperature (310 K), the complexes will exist in blood plasma as >89 % chloro complex, whereas in the cell nucleus significant amounts (45-65 %) of the more reactive aqua adducts would be formed together with smaller amounts of the hydroxo complexes (9-25 %, pH 7.4, [Cl(-)]=4 mM).     

Calibration bias in the determination of polynuclear aromatic hydrocarbons in water

 We present the results of an investigative interlaboratory test to determine the reasons for poor agreement between data from different laboratories for the determination of polynuclear aromatic hydrocarbons in water. Received: 2 July 1998 · Accepted: 1 August 1998     

Baby Verma Modules for Rational Cherednik Algebras

This paper introduces baby Verma modules for symplectic reflectionalgebras of complex reflection groups at parameter t = 0 (theso-called rational Cherednik algebras at parameter t = 0, andpresents their most basic properties. Baby Verma modules arethen used to answer several problems posed by Etingof and Ginzburg,and to give an elementary proof of a theorem of Finkelberg andGinzburg. 2000 Mathematics Subject Classification 16Rxx, 16S38,05E10.