Photoelectrochemical properties and microstructuring of polythiophenes

Photoelectrochemical microstructuring processes have been applied to various classes of semiconductors and especially to intrinsically conducting polymers such as polythiophenes. In this work, a new technique was developed for photoelectrochemical post-structuring of conducting polymers deposited on Pt and p-Si. The surface of a conducting polymer is illuminated with a focused laser beam in a non-aqueous solution in the presence of tetrabutylammonium (TBA) salts. This results in local photoelectrochemical cathodic doping of the polymer and corresponding conductivity increase. Poly-3-phenylthiophene (P3PhT) and polybithiophene (PBT) were investigated in this work. In the case of P3PhT, colourless conducting films are formed, and the post-structuring process could be visualised using conventional optical microscopy. The obtained micropatterns were stable in air and in the anodic doping region, but could be removed by repeated cycling in a potential range including both anodic and cathodic doping. The microstructures were characterised by SEM, EDAX, SECM and other techniques.     

Formation of soluble complexes of cationic polypyridylphenylene dendrimers with DNA

The complexation of DNA with a dendrimer with the successive addition of the dendrimer solution to the solution of DNA leads to the appearance and accumulation of compact particles with a diameter of D _h = 100 ± 10 nm that coexist with particles whose dimensions coincide with those of free DNA molecules (D _h = 450 ± 50 nm). The fraction of large particles decreases regularly; moreover, when the equimolar ratio of charged groups of interacting components is achieved, these particles disappear. The coexistence of practically free DNA molecules and a compact soluble negatively charged complex is confirmed by a sedimentation assay. Further addition of the dendrimer up to a certain ratio of charged groups of the components, much higher than unity, brings about phase separation, while at a large excess of charge groups of the dendrimer (above fivefold), the system turns out to be fully single-phase and composed of compact (110 ± 10 nm) cationic soluble complexes. Owing to the positive charge and small size of complex particles no greater than a critical value of 150 nm, the particles possess an important ability to interact with a positively charged cell membrane and to enter a living cell via endocytosis.     

Interactions between cationic conjugated polyelectrolyte and DNA and a label‐free method for DNA detection based on conjugated polyelectrolyte complexes

The electrostatic complexes of single‐stranded deoxyribonucleic acid (ssDNA) and a cationic conjugated polyelectrolyte (CPE), poly{9,9‐di[3‐(1‐ethyl‐1,1‐dimethyl ammonio)propyl]‐2,7‐fluorenyl‐alt‐1,4‐phenylene dibromide} (PFN), were investigated. Fluorescence emission of PFN solution (10 μmol/L) can be drastically quenched to about one fourth of its original intensity in the presence of a trace amount (2.6 μmol/L) of ssDNA. The effect of oligonucleotide length on the fluorescence quenching behavior was also investigated. In contrast to single‐stranded DNA with 20 bases (ssDNA‐20), ssDNA with 40 bases (ssDNA‐40) induces a relatively higher quenching efficiency and larger red‐shift of PFN emission maximum. The binding constant of ssDNA‐20 and PFN is estimated to be 1.12 × 10²¹. At extremely low concentration (10 nmol/L), PFN can respond to 0.2 nmol/L (or 2 × 10^?10 mol/L) of ssDNA‐20 by significant enhancement of its emission intensity. The result is contrary to the observation in the relative higher concentration, and its mechanism is postulated. Based on the high binding ability of ssDNA with cationic CPE, a label‐free method for ssDNA detection is designed. It uses an electrostatic complex of cationic PFN and an anionic CPE, which exhibits fluorescence resonance energy transfer (FRET) between the two components. Addition of ssDNA improves the FRET extent, indicated by obvious change of fluorescence spectra of the conjugated polyelectrolyte complex. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Highly stable DNA triplexes formed with cationic phosphoramidate pyrimidine alpha-oligonucleotides

The ability of cationic phosphoramidate pyrimidine alpha-oligonucleotides (ONs) to form triplexes with DNA duplexes was investigated by UV melting experiments, circular dichroism spectroscopy and gel mobility shift experiments. Replacement of the phosphodiester linkages in alpha-ONs with positively charged phosphoramidate linkages results in more efficient triplex formation, the triplex stability increasing with the number of positive charges. At a neutral pH and in the absence of magnesium ions, it was found that a fully cationic phosphoramidate alpha-TFO (triplex-forming oligonucleotide) forms a highly stable triplex that melts at a higher temperature than the duplex target. No hysteresis between the annealing and melting curves was noticed; this indicates fast association. Moreover, the recognition of a DNA duplex with a cationic alpha-TFO through Hoogsteen base pairing is highly sequence-specific. To the best of our knowledge, this is the first report of stable triplexes in the pyrimidine motif formed by cationic alpha-oligonucleotides and duplex targets.     

A minimized fluorescent chemosensor array utilizing carboxylate-attached polythiophenes on a chip for metal ions detection

Chemosensor arrays have a great potential for on-site applications in real-world scenarios.However,to fabricate on chemosensor array a number of chemosensors are required to obtain various optical patterns for multianalyte detection.Herein,we propose a minimized chemosensor array composed of only two types of carboxylate-functionalized polythiophene derivatives for the detection of eight types of metal ions.Upon recognition of the metal ions,the polythiophenes exhibited changes in their fluorescence intensity and various spectral shifts.Although both chemosensors have the same polymer backbone and recognition moiety,only the difference in the number of methylene groups contributed to the difference in the fluorescence response patterns.Consequently,the metal ions in aqueous media were successfully discriminated qualitatively and quantitatively by the chemosensor microarray on the glass chip.This study offers an approach for achieving a minimized chemosensor array just by changing the alkyl chain lengths without the necessity for many receptors and reporters.     

Synthesis and characterization of new conjugated soluble polythiophenes with excellent reversible electrochemical properties

A series of five new conjugated polythiophene (PT) derivatives containing piperidinyl groups as a side chain were synthesized by ferric trichloride oxidization. All of the polymers were soluble in common organic solvents, and their high regioregularity were confirmed by ¹H‐NMR. The weight‐average molar masses ranged from 5931 to 22,955 g/mol with a low polydispersity index ranging from 1.18 to 1.79. The fluorescence emission maximum of poly[3‐(N‐methyl propionate–4′‐piperidine)methylene–thiophene] in the films was 725 nm in the yellow–red region, higher than that of the other PT derivatives. All five polymers exhibited reversible p‐doping/dedoping (oxidation/reneutralization) processes; this indicated that these polymers could be applied in electrical equipment in the doping state. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Recent advances in transistor performance of polythiophenes

Polythiophenes have long played a major role in the field of conducting polymers due to their relative ease of synthesis, good thermal and oxidative stability, high charge carrier mobility and ease of processing and they have found widespread use in electronic applications such as field-effect transistors (FETs), organic photovoltaics (OPVs), light-emitting diodes (LEDs) and electrochromic displays (ECDs). In this review, we summarize the most important synthetic approaches to thiophene-, thienothiophene- and other fused thiophene-based polymers, highlight a number of significant findings relating to their properties with an emphasis on device performance in organic field-effect transistors and reflect on existing challenges and future opportunities in the field.     

Advances in molecular design and synthesis of regioregular polythiophenes

Regioregular poly(3-alkylthiophene)s (rrP3ATs) are an important class of pi-conjugated polymers that can be used in plastic electronic devices such as solar cells and field-effect transistors. rrP3ATs can be ordered in three dimensions: conformational ordering along the backbone, pi-stacking of flat polymer chains, and lamellar stacking between chains. All of these features lead to the excellent electrical properties of these materials. Creative molecular design and advanced synthesis are critical in controlling the properties of the materials as well as their device performance. This Account reports the advances in molecular design of new functional polythiophenes as well as the associated polymerization methods. Many functionalized regioregular polythiophenes have been designed and synthesized and show fascinating properties such as high conductivity, mobility, chemosensitivity, liquid crystallinity, or chirality. The methods for the synthesis of rrP3ATs are also applicable to other functional side chains. Di- and triblock copolymers consisting of rrP3AT and polyacrylate or polystyrene have also been successfully synthesized, which can facilitate the assembly of the polythiophene segments. The synthesis of rrP3ATs has evolved into a simple and economical system in which the synthesis can be carried out quickly at room temperature and is thus suitable for large-scale manufacturing. Intensive study has revealed that the regioregular polymerization of 3-alkylthiophenes proceeds by a chain-growth mechanism and can be made into a living system. This feature enables precise control of the molecular weight and facile end-group functionalization of the polymer chains, leading to tailor-made regioregular polythiophenes for specific applications. In addition, researchers have recently designed and synthesized regiosymmetric polythiophenesthese are regioregular but not coupled in a head-to-tail fashionby various methods. These reports indicate that these regiosymmetric polymers show very high mobilities when used in field-effect transistors due to their highly ordered structure. The remarkable performance of regioregular polythiophenes in recent years has allowed for the rapid development in printable electronics and seems destined to lead to further advances in this field.     

Optoelectronic properties of thiazole‐based polythiophenes

In this work, two thiazole‐containing monomers N‐(thiazol‐2‐yl)?2‐(thiophen‐3‐yl)acetamide (ThDBTH) and N,N′‐([4,4′‐bithiazole]‐2,2′‐diyl)bis(2‐(thiophen‐3‐yl)acetamide) (Th₂DBTH) were synthesized through amidification reaction of 2‐(thiophen‐3‐yl)acetyl chloride with aminothiazole derivatives and characterized by FTIR and ¹H and ¹³C‐NMR. The monomers were subjected to electrochemical polymerization and optoelectronic properties of the resultant conducting polymers were investigated. Additionally, copolymerization of ThDBTH in the presence of thiophene was achieved. PThDBTH, PTh₂DBTH, and P(ThDBTH‐Th) exhibited optical band gaps of 2.15, 2.30, and 1.95 eV, respectively. Switching time and optical contrast of the polymers were evaluated via kinetic studies. The P(ThDBTH‐Th) revealed satisfactory switching time and appropriate optical contrast of 1.27 s and 24.97%, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42206.     

New regioregular polythiophenes functionalized with sulfur-containing substituents for bulk heterojunction solar cells

Organic photovoltaic devices fabricated with polythiophenic derivatives and single-walled carbon nanotubes (SWCNT)s have been assembled and tested. For this purpose, some new regioregular polythiophenes with different sulfur-containing groups in the terminal position of a hexamethylenic side chain were prepared using direct and indirect polymerization routes. The optical features of the synthesized polymers were examined and compared by registering their UV–Vis spectra in different solvent/non-solvent systems and in film; their thermal stability, electrical conductivity, cyclic voltammetry and photovoltaic properties were carefully analyzed. In particular, the two samples bearing the sulfinyl group in side chain showed better chromic responses, enhanced self-assembling capabilities, more extended conjugation length, higher electrical conductivity and very promising photovoltaic performances, when compared to those of analogous systems reported on up to now.     

Fluorescence detection of single-nucleotide polymorphism with single-strand triplex-forming DNA probes

Triple-helix-forming oligonucleotides (TFOs) are widespread in the genome and have been found in regulatory regions, especially in promoter zones and recombination hotspots of DNA. To specifically detect these polypurine sequences, we designed and synthesized two dual pyrene-labeled single-strand oligonucleotide probes (TFO-FPs) consisting of recognition, linker, and detection sequences. The hybridization processes of TFO-FPs with target polypurine oligonucleotides involve both Watson-Crick and Hoogsteen base-pairings. Through double sensing of oligonucleotide sequences, single mutations of target oligonucleotides are detected by monitoring changes in pyrene fluorescence. The high specificities of the probes are maintained over a wide temperature range without sacrifice of hybridization kinetics.     

Optical detection of thermal transitions in high polymers

This report describes a series of recent experiments in which various thermal transitions including stress relaxations and glass transitions in high polymers were characterized by observing birefringence changes during heating and cooling. An automatic recording device employing a hot stage, polarizing microscope, photocell, and chart recorder was employed in these investigations. A general discussion of the utility and advantages of the technique of thermo-optical analysis (TOA) as well as its deficiencies is presented. Characteristic birefringence–temperature profiles of a number of amorphous and semicrystalline polymers are included.     

阳离子PLGA纳米颗粒作为核酸疫苗递送载体的能力及其特性评价

目的对阳离子聚乳酸-羟基乙酸共聚物[poly(D,L-lactide-co-glycolide),PLGA]纳米颗粒作为核酸疫苗载体的能力及其特性进行评价。方法采用双重乳化法制备阳离子PLGA纳米颗粒,检测其粒径分布和表面电势,获得合成的最适方案。通过考察其形貌、吸附效率、抵抗核酸酶降解能力、细胞毒性、细胞摄取及转染真核表达质粒的能力,分析其作为核酸疫苗载体的适用性及可行性。结果由两种试剂修饰PLGA制备的纳米颗粒粒径分布、表面电势及分散性最佳;透射电镜及扫描电镜下观察粒径均一且呈规则球形;对质粒DNA的吸附效率可达65%;能够有效保护吸附于纳米颗粒的质粒DNA免受核酸酶降解;两种细胞系中的细胞毒性试验均显示细胞存活率高于80%;共聚焦显微镜下可观察到其能被细胞内化;间接免疫荧光试验结果表明,其能有效转染真核表达质粒并使其正确表达。结论成功制备了具有递送核酸疫苗能力的阳离子PLGA纳米颗粒,为核酸疫苗载体的发展奠定了理论基础。     

阳离子型Gemini表面活性剂共振光散射法测定DNA及相互作用机理的研究

在酸性介质(pH=3.51)中,脱氧核糖核酸(DNA)能显著地增强阳离子型Gemini表面活性剂(G14-4-14)的共振光散射信号,据此提出了G14-4-14共振光散射法测定DNA的新方法,并对介质酸度、离子强度、G14-4-14浓度及共存物质干扰等实验条件进行了优化。在最佳条件下绘制了工作曲线,该方法线性范围为0～2760μg.L-1,检出限为7.79μg.L-1,用于合成样品的测定,结果令人满意。以芘(pyrene)为荧光探针,应用稳态荧光法探讨了G14-4-14与DNA的相互作用,并运用红外光谱及共振光散射光谱初步探讨了G14-4-14与DNA相互作用的机理。     

Water‐soluble ionic polythiophenes for biological and analytical applications

Ionic polythiophenes are important conjugated polymers because of their excellent optical properties and water solubility. They are classified as cationic, anionic and zwitterionic conjugated polyelectrolytes. This review article describes concisely their biological and analytical applications. The specific detection of different negatively charged biomolecules such as DNA and adenosine triphosphate, anions like halides and toxic pseudo‐halide (CN ^?) and environmental pollutants, e.g. surfactants, is discussed. The conformational changes of cationic polythiophenes (CPTs ) induced by various analytes due to formation of ionic conjugates and the cooperative responses of all segments cause dominant signal amplification even in the presence of a small perturbation. In addition, reactive oxygen scavenging, antimicrobial photosensitizing and cell imaging applications of CPTs are documented. Use of anionic polythiophenes for sensing of protamine and cations like Cu²⁺ and Ca²⁺ is also discussed. Finally, sensing of DNA , peptides and surfactants by zwitterionic polythiophenes is included. The concluding part discusses future prospects. © 2016 Society of Chemical Industry     

Nanomorphology-driven two-stage hole mobility in blend films of regioregular and regiorandom polythiophenes

We report the nanomorphology-driven two-stage hole mobility in the blend films of regioregular and regiorandom poly(3-hexylthiophene) (P3HT) polymers of which regioregularity was 92.2% and 33.0%, respectively. The hole mobility of blend films was measured by employing a top-contact type organic field-effect transistor which has an aromatic polyimide gate insulating layer and silver source/drain electrodes. Results showed that the hole mobility of blend films was suddenly reduced as large as two orders of magnitude as the bulk regioregularity of blend films decreased from 89.8% to 86.3%, even though the hole mobility change was far less than one order of magnitude after and before this boundary condition. The discontinuous two-stage hole mobility trend has been attributed to the destruction of P3HT chain ordering/alignment in the blend films at the boundary blend composition, as evidenced from the huge changes in optical absorption coefficient, surface nanomorphology, and in-plane/out-of-plane nanostructures in the blend films.     

Electropreparation and electrochemical stability of polythiophenes in acetonitrile containing anhydrous HBF4

The electrooxidation behavior of thiophene and 3‐methylthiophene on a Pt surface in an acetonitrile + tetrabutylammonium tetrafluoroborate solution were investigated. The electropolymerization of these monomers was studied in neutral, acidic, and basic media. The effects of thiophene concentration and the added acid were elucidated. The polythiophene and poly(3‐methylthiophene) films formed were characterized by their cyclic voltammograms in a blank solution and dry conductivities were measured. Electrochemical properties of these polymers in the same medium were investigated in the absence and in the presence of added anhydrous acid and base. The behavior of the freshly prepared films was compared with that which lost its electroactivity as a result of electrooxidation using cyclic voltammetry, controlled potential coulometry, and FTIR spectroscopy. The mechanisms related to the formation of the polymers and their electroactivity loss were proposed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 312–322, 2000     

Flotation of rutile with anionic and cationic collectors

Results are presented which indicate the effect of pH and flotation-collector type upon the flotation rates of natural rutile particles. Above pH ～2.5, flotation rate decreases with increasing pH for anionic collectors and increases with increasing pH for a cationic collector. These results are in agreement with expectations from the known electrokinetic properties of the mineral. Also, for a fixed pH, the rate of flotation is influenced by the length of the carbon chain associated with the collecting ion, and, for any one collector, by its concentration in solution. Below pH ～2.5, the flotation rate with anionic collectors decreases with fall in pH, whereas with the cationic type a small increase in rate is shown as pH1 is approached.     

DNA recognition and superstructure formation by helix-turn-helix proteins

The way helix-turn-helix proteins recognize DNA is analysedby comparing their sequences, structures, and binding specificities.Individual recognition helices in these proteins bind to fourDNA base pairs with the same geometry. However, pairs of recognitionhelices in the protein dimers can have different separationsand orientations. These differences are used for discriminatingbetween DNAs which have different superstructures, in particular,different numbers of base pairs between sets of the four basepairs.