Excess polarizabilities upon the first dipole‐allowed excitation of some conjugated oligomers

This paper presents theoretical predictions for the excess polarizabilities upon excitation from the ground state to the first dipole‐allowed excited state (1¹B_u) of some conjugated oligomers. The excess polarizability was obtained by simulating the Stark shift, which was predicted by the time‐dependent density functional theory (TDDFT) with the hybrid Becke‐3 Lee–Yang–Parr (B3LYP) potential. The Stark shift in solution was simulated by employing the non‐equilibrium integral equation formalism polarizable continuum model (IEFPCM). All the model molecules considered in this study were fully optimized by the Hartree–Fock (HF) method and the density functional theory (DFT) with the B3LYP potential, respectively. For diphenylpolyenes, the excess polarizabilities displayed by the DFT/B3LYP‐optimized geometries are more reasonable than those displayed by the HF‐optimized geometries when compared with the experimental results. However, this feature is not clearly demonstrated by our results in the cases of oligo(phenylenevinylene)s (OPVs). Copyright © 2008 John Wiley & Sons, Ltd.     

X‐ray‐induced degradation of OEG‐terminated SAMs on silica surfaces during XPS characterization

Oligo ethylene glycol layers are widely used in biosensor applications, mainly for their anti‐fouling abilities. Such surfaces are often characterized by X‐ray photoelectron spectroscopy (XPS) as this method allows a precise determination of the surface chemical composition. We show herein that X‐rays used during XPS characterization quickly and significantly degrade oligo ethylene glycol immobilized onto silica substrates. It is therefore necessary to introduce a correcting factor to assess the true (i.e. without degradation) corresponding ether contribution in the XPS spectrum of such organic layers. Eventually, fluorescence scans show the loss of anti‐fouling properties of the degraded surface, leading to greater amounts of adsorbed (fluorescently labeled) protein. Copyright © 2015 John Wiley & Sons, Ltd.     

串联固相萃取法选择性富集白花蛇舌草中的环烯醚萜苷类成分

研究了从白花蛇舌草水提取物中选择性富集环烯醚萜苷类成分的方法。该方法采用硅胶基质的寡聚乙二醇(OEG,实验室自合成)和ODS两种填料依次作为固定相,对白花蛇舌草水提醇沉样品进行固相萃取,并以超高效液相色谱(UPLC)系统对在富集的各个阶段得到的产物进行了色谱表征。实验结果表明,采用该方法得到的终产物的产率为8.21%。从UPLC谱图中可以看出固相萃取环烯醚萜苷类成分选择性富集的过程。终产物中14种典型的环烯醚萜苷类化合物含量明显升高,可达白花蛇舌草水提物的6.1倍,回收率为50.1%,富集效果明显。因此,将白花蛇舌草水提物醇沉后依次经过OEG柱与ODS柱的串联固相萃取可选择性地富集环烯醚萜苷类成分。该方法操作步骤较少,操作简便,选择性好,提取效率较高,富集效果明显。     

基于荧光素标记的DNA-Cu(Ⅱ)络合物的荧光增强型氰根离子传感器

利用铜离子与荧光素标记的寡核苷酸链、氰根离子结合能力的差异,发展了一种水相中氰根离子检测的新方法.研究表明,该检测方法可以较灵敏地检测水相中的氰根离子,其检测下限达到0.02μmol/L,且具有较好的选择性和潜在的实际应用价值.     

Oligo(p‐phenyleneethynylene) (OPE) Molecular Wires: Synthesis and Length Dependence of Photoinduced Charge Transfer in OPEs with Triarylamine and Diaryloxadiazole End Groups

The systematic synthesis and photophysical, electrochemical and computational studies on an extended series of triphenylamine‐[C?C‐1,4‐C₆H₂(OR)₂]_n‐C?C‐diphenyl‐1,3,4‐oxadiazole dyad molecules (the OR groups are at 2,5‐positions of the para‐phenylene ring and R=C₆H₁₃; n=0–5, compounds 1 , 2 , 3 , 4 and 5 , respectively) are reported. Related molecules with identical end groups, triphenylamine‐C?C‐1,4‐C₆H₂(OR)₂‐C?C‐triphenylamine (R=C₆H₁₃; 6 ) and diphenyl‐1,3,4‐oxadiazole‐[C?C‐C₆H₂(OR)₂]₂‐C?C‐diphenyl‐1,3,4‐oxadiazole (R=C₆H₁₃; 7 ) were also studied. These D–B–A 1 – 5 , D–B–D 6 and A–B–A 7 (D=electron donor, B=bridge, A=electron acceptor) systems were synthesized using palladium‐catalysed cross‐coupling reactions of new p‐phenyleneethynylene building blocks. Steady‐state emission studies on the dyads 1 – 5 reveal a complicated behavior of the emission that is strongly medium dependent. In low polarity solvents the emission is characterized by a sharp high‐energy peak attributed to fluorescence from a locally excited (LE) state. In more polar environments the LE state is effectively quenched by transfer into an intramolecular charge‐transfer (ICT) state. The medium dependence is also observed in the quantum yields (QYs) which are high in cyclohexane and low in acetonitrile, thus also indicating charge‐transfer character. Low‐temperature emission spectra for 2 – 5 in dichloromethane and diethyl ether also reveal two distinct excited states, namely the LE state and the conventional ICT state, depending on solvent and temperature. Hybrid DFT calculations for 1 – 7 establish that the OPE bridge is involved in both frontier orbitals where the bridge character increases as the bridge length increases. Computed TD‐DFT data on 1 – 5 assign the emission maxima in cyclohexane as LE transitions. Each time‐resolved emission measurement on 2 – 7 in cyclohexane and diethyl ether reveals a wavelength dependent bi‐exponential decay of the emission with a fast component in the 5–61 ps range on blue detection and a slower approximately 1 ns phase, independent of detection wavelength. The fast component is attributed to LE fluorescence and this emission component is rate limited and quenched by transfer into an ICT state. The fast LE fluorescence component varies systematically with conjugation length for the series of D–B–A dyads 2 – 5 . An attenuation factor β of 0.15 Å^?1 was determined in accordance with an ICT superexchange mechanism.     

The Effect of Oligo(Ethylene Oxide) Side Chains: A Strategy to Improve Contrast and Switching Speed in Electrochromic Polymers

Solution-processable electrochromic polymers (ECPs) with high performance are urgently needed for extensive applications. Nevertheless, they suffer from slow switching speed because of low ionic conductivities. Herein, we present an effective strategy to improve the contrast and switching speed in ECPs via facile side-chain engineering. A novel electrochromic thieno[3,2-b]thiophene-based polymer (PmOTTBTD) is designed and successfully synthesized by introducing oligo(ethylene oxide) side chains with high ionic conductivity. Compared to the counterpart POTTBTD without modification by oligo(ethylene oxide) chains, PmOTTBTD demonstrates nearly double contrast (42 % vs. 24 %) with a fast oxidation switching process that just takes half of the time when detected under 400 nm, as well as much higher coloration efficiencies (e. g. 239.04 cm² C⁻¹ vs. 226.26 cm² C⁻¹ @ 400 nm and 314.04 cm² C⁻¹ vs. 174.00 cm² C⁻¹ @ 650∼700 nm). Besides, PmOTTBTD exhibits excellent stability with negligible decay after 3000 cycles. Our work suggests a facile strategy that could be adopted to realize high-performance ECPs via molecular design tuning.     

Oligo(p-phenylene ethynylene)-BODIPY derivatives: synthesis, energy transfer, and quantum-chemical calculations

The synthesis and energy‐transfer properties of a series of oligo(p‐phenylene ethynylene)–BODIPY ( OPEB ) cassettes are reported. A series of oligo(p‐phenylene ethynylene)s ( OPE s) with different conjugated chain lengths as energy donor subunit in the energy‐transfer system were capped at both ends with BODIPY chromophores as energy‐acceptor subunits. The effect of the conjugated chain of OPE s on energy transfer in the OPEB cassettes was investigated by UV/Vis and fluorescence spectroscopy and modeling. With increasing number n of phenyl acetylene units (n=1–7), the absorption and emission maxima of OPEn are bathochromically shifted. In the OPEBn analogues, the absorption maximum assigned to the BODIPY moieties is independent of the length of the OPE spacer. However, the relative absorption intensity of the BODIPY band decreases when the number of phenyl acetylene units is increased. The emission spectra of OPEBn are dominated by a band peaking at 613 nm, corresponding to emission of the BODIPY moieties, regardless of whether excitation is at 420 or 550 nm. Furthermore, a very small band is observed with a maximum between 450 and 500 nm, and its intensity relative to that of the BODIPY emission increases with increasing n, that is, the excited state of OPE subunits is efficiently quenched in OPEBn by energy transfer to the BODIPY moieties. Energy transfer (ET) from OPEn to BODIPY in OPEBn is very efficient (all Φ_ET values are greater than 98 %) and only slightly decreases with increasing length of the OPE units. These results are supported by theoretical studies that show very high energy transfer efficiency (Φ_ET>75 %) from the OPE spacer to the BODIPY end‐groups for chains with up to 15–20 units.     

Radical polymerization of ethyl acrylate with dead end polymerization conditions

The radical polymerization of ethyl acrylate (EA) with 4,4^′-azobis(4-cyanovaleric)acid as initiator was investigated in propionitrile at 363 K in order to obtain carboxy-telechelic oligo(ethyl acrylate). The results of functionality and molecular weights showed that a transfer reaction had occurred. A molecular weight study was performed in order to show the importance of transfer to solvent due to the high reactivity of the EA radical. Finally, the radical polymerization was investigated at very low temperature (253-273 K), using a redox system initiation. A behavior of dead end polymerization was observed but the activation energy of propagation for EA is still high and does not allow the synthesis of a telechelic oligomer.