Synthesis and Electropolymerization of 2-(3-Thienylethyl)-3-thiopheneacetate

Conducting polymers offer great promise in the development of electronic devices, displays and sensors. In that regard, biomolecules can be attached to these polymers via functional groups, but the presence of such groups oftentimes hinders polymerization.1-3 One strategy is to polymerize a functionalized monomer precursor of a conducting polymer, followed by reaction of the dangling functional groups of the polymer with appropriately functionalized labels. An attractive functionalized thiophene for that purpose is 3-thienylethanol. Unfortunately, however, this monomer is not polymerizable.1,2 Thus, 3-thienylethanol has been esterified, followed by co-polymerization with 3-methylthiophene (3-MT), and subsequent hydrolysis of the ester to the free alcohol.1,2 Here, we present a viable alternative, whereas we have synthesized monomer 1 from commercially available 3-thiopheneacetic acid and 2-(3-thienylethanol). Monomer 1 was electropolymerized both by itself and as a copolymer with 3- methylthiophene (3-MT). The ester linkage was reduced with LiAlH4, and the resulting hydroxyl groups were re-esterified by reaction with acetyl chloride. The functional group transformations were followed by FT-IR

Protection of 2-(3-Thienyl)ethanol with 3-Thienylacetic Acid and Hard Cross- Linked Conducting Films by Electropolymerization of the Ester

The ester (compound 1) of 2-(3-thienyl)ethanol (T-etOH) with 3-thienylacetic acid was synthesized as a monomer whose two thiophene groups could be electropolymerized independently, becoming members of different polymer chains in a highly-crosslinked highly-insoluble polymer. Indeed, 1 was electropolymerized successfully alone and together with 3-methylthiophene (3MeT). Films of poly(1) are hard (3H, as opposed to less than 6B for poly(3MeT)), and the close proximity of the polymeric strands creates pi-stacking interactions. The behavior of 1 suggests that by: (a) limiting the potential used for the oxidation of monomeric esters of T-etOH at the foot of their oxidation waves (less than 1.8 V vs. Ag/AgCl); and, (b) compensating for the decrease in the electrogenerated radical concentration by increasing the monomer concentration, practically all esters of T-etOH should be electropolymerizable. This was confirmed by durable film formation from the archetypical ester of T-etOH, the 2-(3-thienyl)ethyl acetate (T-etOAc), whose homo-electropolymerization is reported for the first time

Au279(SR)84: The Smallest Gold Thiolate Nanocrystal That Is Metallic and the Birth of Plasmon

We report a detailed study on the optical properties of Au279(SR)84 using steady-state and transient absorption measurements to probe its metallic nature, timedependent density functional theory (TDDFT) studies to correlate the optical spectra, and density of states (DOS) to reveal the factors governing the origin of the collective surface plasmon resonance (SPR) oscillation. Au279 is the smallest identified gold nanocrystal to exhibit SPR. Its optical absorption exhibits SPR at 510 nm. Powerdependent bleach recovery kinetics of Au279 suggests that electron dynamics dominates its relaxation and it can support plasmon oscillations. Interestingly, TDDFT and DOS studies with different tail group residues ( 12CH3 and 12Ph) revealed the important role played by the tail groups of ligands in collective oscillation. Also, steady-state and timeresolved absorption for Au36, Au44, and Au133 were studied to reveal the molecule-to-metal evolution of aromatic AuNMs. The optical gap and transient decay lifetimes decrease as the size increases

Silica Aerogels Doped with Ru(II) Tris 1,l0-Phenanthro1ine)-Electron Acceptor Dyads: Improving the Dynamic Range, Sensitivity and Response Time of Sol-Gel Based Oxygen Sensors

Complexes 1 and 2 were characterized in fluid and frozen solution and as dopants of silica aerogels. The intramolecular quenching efficiency of pendant 4-benzoyl-N-methylpyridinium group (4BzPy) is solvent dependent: emission is quenched completely in acetonitrile but not in alcohols. On the other hand, N-benzyl-N'-methylviologen (BzMeV) quenches the emission in all solvents completely. The differences are traced electrochemically to a stronger solvation effect by the alcohol in the case of 1. In fiozen matrices or absorbed on the surfaces of silica aerogel, both 1 and 2 are photoluminescent. The lack of quenching has been traced to the environmental rigidity. When doped aerogels are cooled to 77K, the emission shifts to the blue and its intensity increases in analogy to what is observed with Ru(II) complexes in media undergoing fluid-to-rigid transition. The photoluminescence of 1 and 2 from the aerogel is quenched by oxygen diffusing through the pores. In the presence of oxygen, aerogels doped with 1 can modulate their emission over a wider dynamic range than aerogels doped with 2, and both are more sensitive than aerogels doped with Ru(II) tris(1,l0- phenanthroline). In contrast to frozen solutions, the luminescent moieties in the bulk of aerogels kept at 77K are still accessible, leading to more sensitive platforms for oxygen sensors than other ambient temperature configurations

Au38(SPh)24: Au38 Protected with Aromatic Thiolate Ligands

Au38(SR)24 is one of the most extensively investigated gold nanomolecules along with Au25(SR)18 and Au144(SR)60. However, so far it has only been prepared using aliphatic-like ligands, where R = 12SC6H13, 12SC12H25 and 12SCH2CH2Ph. Au38(SCH2CH2Ph)24 when reacted with HSPh undergoes core-size conversion to Au36(SPh)24, and existing literature suggests that Au38(SPh)24 cannot be synthesized. Here, contrary to prevailing knowledge, we demonstrate that Au38(SPh)24 can be prepared if the ligand exchanged conditions are optimized, under delicate conditions, without any formation of Au36(SPh)24. Conclusive evidence is presented in the form of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), electrospray ionization mass spectra (ESI-MS) characterization, and optical spectra of Au38(SPh)24 in a solid glass form showing distinct differences from that of Au38(S-aliphatic)24. Theoretical analysis confirms experimental assignment of the optical spectrum and shows that the stability of Au38(SPh)24 is not negligible with respect to that of its aliphatic analogous, and contains a significant component of ligand 12ligand attractive interactions. Thus, while Au38(SPh)24 is stable at RT, it converts to Au36(SPh)24 either on prolonged etching (longer than 2 hours) at RT or when etched at 80 \ub0C

Crystal Structure and Theoretical Analysis of Green Gold Au30(S-tBu)18 Nanomolecules and Their Relation to Au30S(S-tBu)18

We report the complete X-ray crystallographic structure as determined through single-crystal X-ray diffraction and a thorough theoretical analysis of the green gold Au30(S-tBu)18. While the structure of Au30S(S-tBu)18 with 19 sulfur atoms has been reported, the crystal structure of Au30(S-tBu)18 without the \u3bc3-sulfur has remained elusive until now, though matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) data unequivocally show its presence in abundance. The Au30(S-tBu)18 nanomolecule not only is distinct in its crystal structure but also has unique temperature-dependent optical properties. Structure determination allows a rigorous comparison and an excellent agreement with theoretical predictions of structure, stability, and optical response

Isolation and Demonstration of the Elusive Concentration-gradient Paramagnetic Force

Using classical electrochemistry, it is demonstrated that the concentration-gradient paramagnetic force, FC, is a body force proportional to B2 acting parallel to the concentration gradient of electrogenerated radicals. FC can balance gravity, holding volumes of solution wherein mass transfer continues to take place by diffusion. In contrast to usual levitation forces, FC does not depend on field gradients and may be present even in homogeneous magnetic fields. Understanding the properties of FC is relevant to magnetic confinement and levitation and is speculated even to propulsion with objects having permanent susceptibility gradients

Non-additive Voltammetric Currents from Multicomponent Systems of Redox-active Substances

Mixtures of two redox-active compounds with dissimilar diffusion coefficients produce non-additive mass-transfer limited currents. Similarly, in the potential range where three redox-active species, decamethylferrocene (dMeFc), ferrocene (Fc) and N-methylphenothiazine (MePTZ), are oxidized simultaneously (Eo\u27MePTZ \u3e Eo\u27Fc \u3e Eo\u27dMeFe) with rates controlled by linear diffusion, electrogenerated radicals diffusing outwards from the electrode react with original species diffusing towards the electrode from the bulk; thus, Fc.+ reacts with dMeFc producing Fc and dMeFc.+, while MePTZ.+ reacts with both Fc and dMeFc producing MePTZ together with Fc.+ and dMeFc.+. These processes replace the flux of dMeFc with Fc at the second current plateau (referring to normal pulse voltammetry), and the fluxes of both dMeFc and Fc with MePTZ at the third plateau. Analogous results have been obtained and analyzed with two other multicomponent systems undergoing multiple sequential electron transfers, namely dMeFc/Fc/TPTA and dMeFc/TTF (TPTA: tri-N-p-tolylamine; TTF: tetrathiafulvalene). Since the diffusion coefficients of the three species are different, the mass-transfer limited currents of the second and third oxidation waves are not equal to the sum of the currents that each component would have produced if it were in the solution alone. Numerical simulations of the experimental voltammograms using diffusion coefficients measured independently support this mechanism. Multicomponent systems are encountered frequently in practice and our results identify one significant (∼10%) source of error in quantitative voltammetric analysis. Ways around the problem are summarized in the conclusions section

Monolayer-Protected Clusters: Versatile Materials of Electrochemical Importance

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