Theoretical study of the photochemistry of a reversible three-state bis-thiaxanthylidene molecular switch

The ground- and the lowest singlet excited-state potential energy surfaces of the bis-thiaxanthylidene (3) molecular switch are investigated using a density functional method specifically designed to treat molecular systems typified by strong non-dynamic electron correlation. The results of the theoretical calculations suggest that the unique ability of substituted bis-thiaxanthylidenes to switch between three states of luminescence-non-fluorescent state, blue fluorescent state, and red fluorescent state-can be explained by specific features on the excited state potential energy surface: the potential barrier around the Franck-Condon point of the anti-folded conformer and the existence of conical intersection in the vicinity of the syn-folded conformer. It is suggested that the twisted conformer, if made more stable via chemical modification, should fluoresce in the near-infrared region (λ≈740-760 nm), thus offering a possibility for a four-state switching of luminescence in a single-component molecular system.     

Electropolymerization of Preadsorbed Layers of Some Azine Redox Dyes on Graphite

The redox-active azine dyes Nile blue A (NB) and Toluidine blue O (TB) were electropolymerized after preadsorption onto the surface of graphite electrodes by potential cycling, using an anodic scan limit of 0.9 or 1.0 V vs SCE, where irreversible electrooxidation of the dye proceeds, yielding polymerizable species. Electropolymerization of both dyes is followed by the progressive disappearance of the characteristic current peaks in the cyclic voltammograms, and formation of new ones, shifted by ca. 0.21 V to the positive direction. Also, a decrease and gradual disappearance of the characteristic luminescence at a maximum of 671 nm was observed during the electropolymerization of NB. The resulting electrodes, modified by electropolymerized derivatives of NB and TB, were shown to be able to catalyze the electrooxidation of the coenzyme NADH. Thus, the modified electrodes prepared can be used for amperometric detection of the reduced form of the coenzyme. Copyright 2000 Academic Press.     

White and Red Organic Light Emitting Materials

Derivatives of 2,3-(1,4-dialkoxyaceno)norbornadiene underwent ring-opening metathesis polymerization (ROMP) upon the catalysis of a ruthenium complex to afford the corresponding polymers. The polymeric materials containing anthracene chromophores emit white electro-luminescence, which can be fabricated into light-emitting diodes (LED). The broad emission band is composed of a blue emission from anthracene and a red emission from aggregates. A single layer device, ITO/polymer/Ca/Al, can be turned on at 7V and exhibits maximum intensity 427 cd/m2 at 15 V. A double layer device, ITO/polymer/TPBI/Mg:Ag (TPBI = (2,2′,2"-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)) displayed blue light with turn-on voltage 6 V and maximal intensity 930 cd/m2 at 15 V.Derivatives of bisindolylmaleimide were found to form amorphous solid films which exhibit intensive red luminescence. The property of forming glasses can be ascribed to the nonplanar geometry of these molecules. LED devices were fabricated by a layer of pure dye sandwiched between two charge transporting films. The yellow emission spectrum of the devices utilizing Alq (tris(8-hydoxyquinolinato)aluminum) contains a green component from Alq. Pure red emissions can be achieved by replacing Alq with TPBI. Typical devices can be turned on at ～3 V with maximal intensity 2000 cd/m2. White color devices are under current investigation, in which the green Alq layer is replaced by its blue derivative (bis(2-methyl-8-hydoxyquinolinato)(phenolato)aluminum).     

Tuning orbital energetics in arylene diimide semiconductors. materials design for ambient stability of n-type charge transport

Structural and electronic criteria for ambient stability in n-type organic materials for organic field-effect transistors (OFETs) are investigated by systematically varying LUMO energetics and molecular substituents of arylene diimide-based materials. Six OFETs on n+-Si/SiO2 substrates exhibit OFET response parameters as follows: N,N'-bis(n-octyl)perylene-3,4:9,10-bis(dicarboximide) (PDI-8): mu = 0.32 cm2 V(-1) s(-1), Vth = 55 V, I(on)/I(off) = 10(5); N,N'-bis(n-octyl)-1,7- and N,N'-bis(n-octyl)-1,6-dibromoperylene-3,4:9,10-bis(dicarboximide) (PDI-8Br2): mu = 3 x 10(-5) cm2 V(-1) s(-1), Vth = 62 V, I(on)/I(off) = 10(3); N,N'-bis(n-octyl)-1,6,7,12-tetrachloroperylene-3,4:9,10-bis(dicarboximide) (PDI-8Cl4): mu = 4 x 10(-3) cm2 V(-1) (s-1), Vth = 37 V, I(on)/I(off) = 10(4); N,N'-bis(n-octyl)-2-cyanonaphthalene-1,4,5,8-bis(dicarboximide) (NDI-8CN): mu = 4.7 x 10(-3) cm2 V(-1) s(-1), Vth = 28, I(on)/I(off) = 10(5); N,N'-bis(n-octyl)-1,7- and N,N'-bis(n-octyl)-1,6-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2): mu = 0.13 cm2 V(-1) s(-1), Vth = -14 V, I(on)/I(off) = 10(3); and N,N'-bis(n-octyl)-2,6-dicyanonaphthalene-1,4,5,8-bis(dicarboximide) (NDI-8CN2): mu = 0.15 cm2 V(-1) s(-1), Vth = -37 V, I(on)/I(off) = 10(2). Analysis of the molecular geometries and energetics in these materials reveals a correlation between electron mobility and substituent-induced arylene core distortion, while Vth and I(off) are generally affected by LUMO energetics. Our findings also indicate that resistance to ambient charge carrier trapping observed in films of N-(n-octyl)arylene diimides occurs at a molecular reduction potential more positive than approximately -0.1 V (vs SCE). OFET threshold voltage shifts between vacuum and ambient atmosphere operation suggest that, at E(red1) < -0.1 V, the interfacial trap density increases by greater than approximately 1 x 10(13) cm(-2), while, for semiconductors with E(red1) > -0.1 V, the trap density increase is negligible. OFETs fabricated with the present n-type materials having E(red1) > -0.1 V operate at conventional gate biases with minimal hysteresis in air. This reduction potential corresponds to an overpotential for the reaction of the charge carriers with O2 of approximately 0.6 V. N,N'-1H,1H-Perfluorobutyl derivatives of the perylene-based semiconductors were also synthesized and used to fabricate OFETs, resulting in air-stable devices for all fluorocarbon-substituted materials, despite generally having E(red1) < -0.1 V. This behavior is consistent with a fluorocarbon-based O2 barrier mechanism. OFET cycling measurements in air for dicyanated vs fluorinated materials demonstrate that energetic stabilization of the charge carriers results in greater device longevity in comparison to the OFET degradation observed in air-stable semiconductors with fluorocarbon barriers.     

An amperometric biosensor for glucose based on electrodeposited redox polymer/glucose oxidase film on a gold electrode.

In this paper, we described a glucose biosensor based on the co-electrodeposition of a poly(vinylimidazole) complex of [Os(bpy)2Cl](+/2+) (PVI-Os) and glucose oxidase (GOX) on a gold electrode surface. The one-step co-electrodeposition method provided a better control on the sensor construction, especially when it was applied to microsensor construction. The modified electrode exhibited the classical features of a kinetically fast redox couple bound to an electrode surface and the redox potential of the redox polymer/enzyme film was 0.14 V (vs. SCE). For a scan rate of up to 200 mV s(-1), the peak-to-peak potential separation was less than 25 mV. In the presence of glucose, a typical catalytic oxidation current was observed, which reached a plateau at 0.25 V (vs. SCE). Under the optimal experimental conditions, the steady-state electrooxidation current measured at 0.30 V (vs. SCE) was linear to the glucose concentration in the range of 0-30 mM. Successful attempts were made in blood sample analysis.     

Poly(Neutral Red)/Cholesterol Oxidase Modified Carbon Film Electrode for Cholesterol Biosensing

New amperometric cholesterol oxidase (ChOx) based enzyme biosensors for cholesterol have been developed. The enzyme was immobilised with and without glutaraldehyde cross‐linking on top of carbon film electrodes modified with redox mediators. Mediators tested were: poly(neutral red) (PNR), Prussian blue and cobalt hexacyanoferrates. Amperometric detection of cholesterol showed that PNR/ChOx modified electrodes exhibited the best characteristics; under optimised conditions cholesterol was determined at ?0.4 V vs. SCE with a detection limit of 1.9 µM. The biosensors showed good reproducibility and stability and only a small influence from potential interferents in food. Analyses of cholesterol in egg yolk were successfully performed.     

An electrochemical color-switchable RGB dye: tristable [2]catenane

We propose a design for an electrochemically driven RGB dye based on a tristable [2]catenane, in which the color of the molecule can be switched between Red, Green, and Blue by merely changing voltage. Based on DFT calculations, we conclude that the tristable [2]catenane should consist of a CBPQT4+ ring interlocked with a polyether macrocyle containing DNP (red), TTF (green), and FBZD (blue) units as the tunable RGB color-generating donors. Thus, at controllable voltages 0, V1, and V2, the [2]catenane is expected to display green, blue, and red colors, respectively. The advent of these RGB tristable molecules may have potential applications in low cost paperlike electronic displays.     

High‐Contrast Red–Green–Blue Tricolor Fluorescence Switching in Bicomponent Molecular Film

Highly efficient red–green–blue (RGB) tricolor luminescence switching was demonstrated in a bicomponent solid film consisting of (2Z,2′Z)‐2,2′‐(1,4‐phenylene)bis(3‐(4‐butoxyphenyl)acrylonitrile) (DBDCS) and (2Z,2′Z)‐3,3′‐(2,5‐bis(6‐(9H‐carbazol‐9‐yl)hexyloxy)‐1,4‐phenylene)bis(2‐(3,5‐bis(trifluoromethyl)phenyl)acrylonitrile) (m‐BHCDCS). Reversible RGB luminescence switching with a high ratiometric color contrast (λ_em=594, 527, 458 nm for red, green, and blue, respectively) was realized by different external stimuli such as heat, solvent vapor exposure, and mechanical force. It was shown that Förster resonance energy transfer in the bicomponent mixture could be efficiently switched on and off through supramolecular control.     

Charge-transfer complexation as a general phenomenon in the copigmentation of anthocyanins

Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmentation) is re-interpreted in terms of charge transfer from the copigment to the anthocyanin. Flavylium cations are shown to be excellent electron acceptors (E(red) approximately -0.3 V vs SCE). It is also demonstrated, for a large series of anthocyanin-copigment pairs, that the standard Gibbs free energy of complex formation decreases linearly with EA(Anthoc) - IP(Cop), the difference between the electron affinity of the anthocyanin, EA(Anthoc), and the ionization potential of the copigment, IP(Cop). Based on this correlation, copigmentation strengths of potential candidates for copigments can be predicted.     

邻苯三酚红修饰碳糊电极吸附伏安法测定痕量铜

报道了采用邻苯三酚红修饰碳糊电极测定痕量铜的方法。通过在邻苯二甲酸氢钾 -氢氧化钠 (p H4.5)介质中富集 ,Cu2 +和邻苯三酚红形成络合物富集于电极表面 ,然后转换到 0 .0 50 mol· L-1的 H3PO4 中 ,经阴极还原后再进行阳极溶出伏安法测定。Cu2 +浓度在 1 .6× 1 0 -9～ 2 .8× 1 0 -7mol·L-1范围内与二次导数峰电流呈线性关系 ,检出限达 8× 1 0 -10 mol·L-1。同时 ,对电极反应机理进行了探讨。应用于合金样的测定 ,取得满意的结果。     

Electrochemical and Spectroelectrochemical Studies on Pyridoxine Hydrochloride Using a Poly(methylene blue) Modified Electrode

The electrochemical redox processes of pyridoxine hydrochloride (VB₆) at a poly(methylene blue) film modified glass carbon electrode (PMBE) in a phosphate buffer solution (PBS, pH 8.0) were studied by cyclic voltammetry. The VB₆ electrode reaction with quasi‐reversible characteristics was diffusion‐controlled at low scan rates and adsorption‐controlled at high scan rates. The anodic peak current positive to 0.6 V (vs. SCE) was found to be proportional to the concentration of VB₆ in the range of 0.010 to 1.03 mg?mL^?1 with a detection limit of 1.34 μg mL^?1. Fluorescence and UV‐vis absorption spectroelectrochemical measurements suggest that the pyridine ring was not destroyed over the potential range from ?0.8 to 1 V (vs. SCE), and the electrocatalytic generation of pyridoxal was anodically started at 0.57 V.     

The effects of conductivity and electrochemical doping on the reduction of methemoglobin immobilized in nanoparticulate TiO2 films

Methemoglobin (bovine) is immobilized from aqueous phosphate buffer (pH 5.5) solution into thin porous TiO(2) (anatase) films at ITO electrode surfaces. Films of TiO(2) are produced in a deposition process employing 40 nm diameter TiO(2) nanoparticles suspended in dry methanol followed by calcination. The pore size in these films is sufficient for methemoglobin (ca. 6 nm diameter) to diffuse into the porous structure (over several hours) and to remain immobilized in electrochemically active form. The electrochemical reduction of methemoglobin immobilized in TiO(2) and immersed in aqueous phosphate buffer at pH 5.5 is observed in two steps with (i) a small quasi-reversible voltammetric response at -0.16 V vs. SCE (Process 1) and (ii) an irreversible reduction peak at ca. -0.5 V vs. SCE (Process 2). The irreversible response is recovered only after slow chemical re-oxidation of hemoglobin to methemoglobin. At sufficiently negative applied potential "electrochemical doping" of the TiO(2) host is observed to lead to a considerably enhanced reduction Process 1. TiO(2) can be temporarily switched from a non-conducting (irreversible electron transfer) into a conducting (reversible electron transfer) state.     

A combined computational and experimental study on DNA-photocleavage of Ru(II) polypyridyl complexes [Ru(bpy)2(L)]2+ (L = pip, o-mopip and p-mopip)

A combined computational and experimental study on DNA-photocleavage by Ru(II) polypyridyl complexes [Ru(bpy)2(L)]2+ 1-3 (bpy = 2,2-bipyridine; L: pip = 2-phenylimidazo[4,5-f]1,10-phenanthroline, o-mopip = 2-(2-methoxyphenyl)imidazo[4,5-f]1,10-phenanthroline and p-mopip = 2-(4-methoxyphenyl)imidazo[4,5-f]1,10-phenanthroline) has been carried out. The DNA-photocleavage behavior of these complexes was comparably measured by the gel electrophoresis experiments. The experimental results show that they can induce considerable DNA-photocleavage, and have different DNA-photocleavage efficiencies (phi) following the order phi (1) < phi (2) < phi (3). In order to understand their DNA-photocleavage mechanism and trend, the theoretical studies on the geometric and electronic structures of these complexes in the ground state (S0), the first singlet excited state (S1) and triplet excited states (T1), have been carried out using the density functional theory (DFT/TD-DFT), Hartree-Fock (HF) and configuration interaction singles (CIS) methods. In particular, the reduction potentials (E*red) of the excited complexes in aqueous solution, which seem to be closely responsible for the DNA-photocleavage behavior, were calculated to be 0.966 V (vs. SCE) for complex , 1.024 V (vs. SCE) for complex and 1.030 V (vs. SCE) for complex , respectively. Such computational results show that the reduction potentials of the excited complexes reach the theoretical range for oxidizing some DNA-bases, and follow the order E*red (1) < E*red (2) < E*red (3). Therefore, here, in addition to the general theoretical explanation of their DNA-photocleavage mechanism according to our recent report, a further explanation on the trend of their DNA-photocleavage efficiencies, i.e., phi (1) < phi (2) < phi (3), was reasonably carried out, on the basis of the calculated electrochemical properties in the excited states as well as general photochemical insights.     

Blue‐Emissive Cobalt(III) Complexes and Their Use in the Photocatalytic Trifluoromethylation of Polycyclic Aromatic Hydrocarbons

Room‐temperature luminescent Co^III complexes ( 1 and 2 ) are presented that exhibit intense ligand‐to‐metal and ligand‐to‐ligand charge transfer absorption in the low‐energy UV region (λ_abs≈360–400 nm) and low‐negative quasi‐reversible reduction events (E^1/2_(red)=?0.58 V and ?0.39 V vs. SCE for 1 and 2 , respectively). The blue emission of 1 and 2 at RT is due to the large bite angles and strong σ‐donation of the ligands, the combined effect of which helps to separate the emissive ³LMCT (triplet ligand‐to‐metal charge transfer) and the non‐emissive ³MC (triplet metal‐centered) states. 1 and 2 were found to be powerful photo‐oxidants (E =2.26 V and 2.75 V vs. SCE of 1 and 2 , respectively) and were used as inexpensive photoredox catalysts for the regioselective mono(trifluoromethylation) of polycyclic aromatic hydrocarbons (PAHs) in good yields (ca. 40–58 %).     

Preconcentration and voltammetric determination of trace myoglobin at a 6-mercaptopurine modified silver electrode

6-Mercaptopurine(6-MP) is covalently modified onto a silver electrode to construct a chemically modified electrode (CME). It exhibits the capability of selectively complexing myoglobin and can be applied as a selective biosensor for this compound. Myoglobin is accumulated onto the CME at 0.32 V (vs. SCE); after exchanging the medium it is determined by differential pulse stripping voltammetry. A cathodic stripping peak is obtained at 0.15 V (vs. SCE) by scanning the potential from 0.35 to –0.1 V. The peak currents are linearly proportional to the concentration of myoglobin in the range of 0.2 ～ 4 μg/mL with a relative standard deviation of 7.8%. The detection limit is about 0.1 μg/mL. The mechanism of the complexation is also discussed.     

酸性大红3R的电化学研究及应用

采用循环伏安法和方波伏安法考察了酸性大红3R在碳糊电极上的伏安行为和反应机理。当扫描速率为0.1 V/s时,在pH 1的0.05 mol/L H2SO4支持电解液中,酸性大红3R有一对峰电位分别是0.74 V和0.72 V（vs.饱和甘汞电极）的氧化峰和还原峰,并且显示吸附控制的2电子单质子的准可逆氧化还原过程。在最佳实验条件下,酸性大红3R的方波氧化峰峰电流与其浓度在2.12&#215;10^-5-3.39&#215;10^-4mol/L范围内呈线性关系,检出限为8.35&#215;10^-6mol/L,由此建立测定酸性大红3R含量的方波伏安法。该方法可用于计算酸性大红3R常规染羊毛与蚕丝的上染率,测定结果与分光光度法一致。     

Broad HOMO-LUMO gap tuning through the coordination of a single phosphine, aminophosphine or phosphite onto a Ru(tpy)(bpy)2+ core

The synthesis of new ruthenium(II) terpyridine bipyridine complexes bearing a phosphorus(III) ligand is presented. The steric and electronic properties of the phosphorus ligand were varied using aminophosphines, alkyl and aryl phosphites and the bulky tri(isopropyl)phosphine. All complexes were characterized by multi-nuclear NMR spectroscopy, mass spectrometry and X-ray diffraction analysis. The electronic properties of the complexes were probed by cyclic voltammetry, absorption and luminescence spectroscopy. The complexes do not show luminescence at room temperature, whereas at 77 K in an alcoholic matrix, emission is observed in the range 600-650 nm with lifetimes of 3.5-5.5 micros, originating from 3MLCT states. The MLCT transition spans over 65 nm, which corresponds to a variation of 0.4 eV in the HOMO-LUMO gap. The oxidation potential of the ruthenium varies over a broad range of 290 mV, from +1.32 V vs. SCE with L = PiPr3 to +1.61 V vs. SCE with L = P(OPh)3. This range is unprecedented upon the variation of a single monodentate ligand coordinated by the same heteroatom in the same oxidation and charge states. This work underlines the specific capacity of phosphorus in bringing up a large variety of electronic properties by changing its substituents.     

聚(3,4-乙撑二氧噻吩)导电织物的制备、结构及其电致变色性能

本文采用原位聚合法, 以耐酸性好的涤纶为基底, 制得了聚(3,4-乙撑二氧噻吩)/涤纶复合导电织物[Poly(3,4-ethylenedioxythiophene)/conducting terylene textile, PEDOT/CTT], 分析了该导电织物的形貌、导电性能及结构, 并对其电致变色性能进行了初步测试. 实验结果表明, 所得到的PEDOT/CTT具有良好的导电性和一定的电致变色性能, 有望在全固态电致变色织物的制备中获得应用.     

The voltammetric behavior of bone marrow of leukaemia and its clinical application

The electrochemical voltammetric behavior of bone marrow of leukaemia has been investigated by a self-devised cytosensing system. The two anodic peaks of erythrocytes (red blood cells, RBC) in bone marrow of leukaemia appeared at 0.73 +/- 0.03 and 0.83 +/- 0.02V vs. SCE, respectively, on the first scan. The anodic peak of leukocytes (white blood cells, WBC) appeared at 0.32 +/- 0.03V vs. SCE. The anodic peak of RBC at 0.83V disappeared when the patients were cured. The experimental results show that the voltammetric behavior of erythrocytes is in constant contact with the initial stage of leukaemia. The cyclic voltammetric behavior of 40 cases of leukaemia including acute myeloid leukaemia (AML) and chronic myeloid leukaemia (CML) and 10 cases of healthy volunteer peripheral blood was studied. The cyclic voltammetric behavior of erythrocytes may provide a simple and specific marker for diagnosis of leukaemia.     

Alternating Current Tensammetry of Tetraphenylborate (TPB) and its Application for Potassium Determination

Alternating‐current polarography of tetraphenylborate ion (TPB) in acetate buffer (pH 4 to 5) or 0.1 to 0.5 M NaCl produces a characteristic tensammetric (pseudocapacitive) peak at ?0.95 V (vs. SCE). Within a limited range (till about 0.2 mM), the tensammetric peak current is proportional to the TPB concentration but it levels off at higher concentration. TPB concentration can also be determined within 5 to 50 μM by measuring the capacity current at ?0.4 V or the differential pulse polarographic peak current at ?0.85 V. The tensammetric peak current was used to determine the solubility of potassium tetraphenylborate in acetate buffer and sodium chloride solutions. Also, a method for amperometric back‐titration of potassium ion was worked out and applied to the analysis of mineral water.