Thiophene pdf

A short summary of this paper. Download Download PDF. Translate PDF. E Warraga,b, Nerea R. Rodriguezb, Inas M.

Nashefc, Martin van Sint Annalandb, J. Ilja Siepmannd, Maaike C. Kroon Email: mkroon pi. The deuterated dimethyl sulfoxide DMSO was used as solvent for all the tested samples. Figure S. Solubility of thiophene in ethylene glycol and glycerol The solubility of thiophene in pure ethylene glycol and glycerol was tested.

The measurements were done following the cloud point method at Table S. Finally the halogen in the termi- nal position of the alkyl substituent was converted into a thiol function. The product is sensitive to oxidation under ambient conditions, e. LiClO4 p. Aldrich , was dried under reduced pressure. This highly reactive intermediate is not isolated and reacts with 1,6 dibromohexane at room temperature to give the 2-alkyl substituted thiophene. The driving force for the reaction is the exergonic formation of LiBr.

The reaction was carried out under ambi- ent conditions and gave a high yield of the regioselec- tively brominated 5-bromo-thien-2yl -bromohexane. This compound was converted to the appropri- V, 0. Monolayer preparation 3.

Contact angle measurements The platinum electrodes were cleaned and the crys- Static contact angles were measured by dipping the talline structure of the surface reorganised by glowing spherical Pt-working electrode partly in water and ac- in a hydrogen p.

The electrode was commodating the dipping depth until the meniscus near cooled under highly pure water and subsequently rinsed the electrode was horizontal. The measurements were with acetonitrile. The contact angle was cal- Pt substrates [15,16] in a 1 mM solution of the thiol in culated from the relation of immersion-height and acetonitrile for 1 s up to several hours.

Ungrafted radius of the electrode [18—20] molecules, that did not specifically adsorb onto the metal surface, were afterwards flushed off with acetoni- 3.

Ellipsometry trile in an ultrasonic bath for 2 min. After this treat- ment the samples were transferred directly into the The thickness of the deposited organic layer was electrochemical cell.

A lens and a small di- aphragm are added in order to reduce the illuminated area to ca. Characterization of adsorbed monolayers gence below 5 mrad [17].

The largest variations of ellipsometric parameters D and C with the layer 3. The voltammograms were analyzed with an according to electromagnetic theory. The and 1. The thickness varies a little in an oppo- LiClO4, in acetonitrile. In order to lower the impedance site way from the index n around 1. Otherwise the index of alkyl capacity of 1 mF was added between the electrolyte and thiol or alkyl silane monolayers is generally taken equal the reference electrode.

The working electrode was a to 1. Consequently we a Pt wire. All potentials ments have been performed at different locations and reported in the paper refer to this electrode.

Possible structures of the adsorbed molecule that might lead to an interaction between the aromatic b-positions. Photoluminescence measurements by solubilizing SAMs prepared on thin gold layers, using the procedure described in the following.

The SAMs were prepared as described above. Fluorescence spectra excitation and emission were detected with a SLM-fluorescence-spectrophotometer. Initially we verified whether the above described method produced samples that could be employed in spectrofluorimetric measurements. Aldrich solubilized in the same solvent. The comparison showed that the shape and the excitation and emission wavelengths of both samples were nearly identical. Results and discussion 4.

Electrochemical beha6ior of the monolayer Fig. Setting the reversal potential mined by considering the total oxidation of the mono- at 0. The surface concentration was confirmed by proportional to the scan rate over the range 50 to reductive desorption of the layer in 0. This cation in acetonitrile. An oxidation potential of is transferred. We attribute depend on the positive reversal potential Ea,r.

As a matter of fact, Fig. These results suggest the occur- of freedom for rotation out of the molecular plane, rence of an anodic over-oxidation of the organic layer, which leads to a significant intramolecular torsion of which is known to lead to a loss of electrochemical the molecule. The effective conjugation length is there- activity. Additionally, in the potential range between fore smaller than for the quasi-planar structure of 0.

The cov- potential in solution. The second, II, and following voltammetric cycles A comparison of the charges transferred during the Fig. Electrochemical coupling of hexyl-terthiophene 3T-hexyl onto an adsorbed monolayer of 3T-hexyl-S — on platin. V shows the disappearance of the previous oxidation peak appears at 0. The cathodic half-cycle shows peak, and the appearance of a new reversible electro- only a small corresponding reduction peak. The oxidation-wave is causing a significant loss of the reversibly transferred followed by a reversible reduction in the negative charges.

The currents are desorption of the SAM. This species be- comes unstable upon cycling to higher potentials. In a Fig. Emission spectra of the coupling product SAM-3T-hexyl — potential-scan up to 0. These electrochemi- film. The diffusion of ions into the polymeric SAM cal results strongly suggest the occurrence of an irre- apparently causes a disorder, that is detected by the versible reaction during the first oxidation of the increase of the angle-hysteresis.

The decrease of the terthiophene SAM. As the electrochemical oxidation of the SAM tion in the first positive sweep, which leads to a new has been carried out in a neutral, thiophene-free elec- molecular architecture, still grafted onto the elec- trolyte, in the absence of any reactive species, it must be trode surface; considered that such increase of conjugation length can 2.

Although a precise 3. Ellipsometry A. A layer in aqueous sulfuric acid 0. The reaction is well described and should 4. Contact angle measurement lead to a sexithiophene derivative. For the molecules. Such an assumption is however highly questionable. As a matter 4. C of fact, dimercapto-6T can be independently generated In view of the poor supporting evidence for the first on a gold or platinum electrode by electrochemical two hypotheses, we argue in favor of an electrochemical oxidative coupling of adsorbed 3T-hexyl-SH with 5- transformation discussed in the following.

However, the terthiophene radical cations, which, as largely described characteristics of such an adsorbed sexithiophene ap- in the literature [22], show a significant reactivity for pear very different from those obtained for the SAM. This coupling demands one electron from polaron and a dication bipolarons at 0.

Furthermore, under the same electrochemical oxidation potential. The newly obtained conjugation conditions, the oxidized SAM shows a rapid degrada- length depends on the position, in the terthiophene tion Fig. Thus, this whole more no decrease of the surface concentration 0. Once formed by an irreversible reaction con- 4.

As a matter of fact, the SAM offers a tion of one electron per terthiophene unit in this latter close packing for the terthiophene molecules, as is redox-process also agrees with the observed second and evident from the distance between two adjacent terthio- following voltammograms II.

In addition, the irre- phene planes which can be calculated from electro- versible dimerization of 3T into an oligothiophene chemical surface analysis. The calculated intermolecular derivative also agrees with the obtained spectral results, distance, comprised between 3. As already discussed in formation of p-dimers.

The occurrence of such p- hypothesis A, a classical a,a-coupling between terthio- dimers has already been considered in the literature phene radical cations cannot take place, as it would [21], and their contribution to the electrical and electro- require the formation of an exocyclic a, a-bond be- chemical properties of oligothiophenes is still debated.

In fact, calculations of a covalent bond between the conducting polymer of the electron spin densities in the radical-cation and the SAM. These was added to the electrolyte during the electrochemical calculations suggest that a b, b-coupling between two investigation of self-assembled monolayers of 3T-hexyl- terthiophene units is theoretically possible, all the more SH on platinum following the procedure described since these terthiophenes are closely packed.

Moreover, below. Anyway the b, b-coupling rate electrolyte. The voltammogram plings, that are known from classical polymerization, shows a shoulder at 0. The nega- terthiophene-based SAMs, when engaged between posi- tive sweep shows a sharp reduction wave at 0. Subsequently the working electrode was phene would be formed Scheme 2a. Steric constraint thoroughly rinsed with dichloromethane CH2Cl2 chro- considerations would favor Scheme 2a, although manorm, Prolabo under ultrasound in order to remove Scheme 2b provides a higher conjugated molecular the excess of di-hexyl-sexithiophene DHS , that was system.

A more precise attribution cannot be proposed formed in the electrolyte and precipitated on the elec- on the basis of the experimental data actually available. The rinsing procedure was repeated until the cyclic voltammogram 4.

Electrochemically induced interfacial reactions of no longer showed the signal of di-hexyl-sexithiophene. The suggested reactions in Scheme 2a, b imply that The obtained voltammetric cycle, Fig. The terthiophenes units unreacted. In that case the pendent voltammograms display a stable and highly reversible a-CH bonds of the terminal thiophene cycles of the electrochemical system, with two oxidation waves at immobilized molecules point upward [19] and should be 0.

All peak currents follow a linear func- thiophene derivatives, that would be introduced into tion of the sweep rate. This modified layer can be the electrolyte. The pre-treated with SAMs containing pendent aromatic shape and the peak potentials of the voltammogramm cycles [24]. Mekhalif et al. The occurrence of this platinum substrates, that had been pre-treated with an compound has been confirmed by the use of fluores- alkylthiol-functionalized benzene.

The increased adhe- cence spectroscopy Fig. This b, b dimerization is further confirmed monolayer of the coupling product hexyl-6T-hexyl-S- by the availability of the terminal a-CH positions of the Pt. During the positive sweep Fig. Nevertheless, a b, b- polaron and bipolaron in the hexyl-6T-hexyl-S-Pt coupling should occur only when the alignment of the within the positive halfcycle. We think Contact angle measurements were also employed to that in bulk systems, such as classical electropolymer- confirm the electrochemical reaction between the ad- ization, the b, b-coupling has only little relevance.

This gain [1] A. Kumar, G. Whitesides, Science Kim, G. Whitesides, L. Lee, S. Smith, M. Prentiss, coupling reaction. Ellipsometric data indicates an average thickness of [4] M. Porter, T. Bright, D. Allara, C. Chidsey, J. Obviously the yield of the [5] L. Dubois, B.