Synthesis, characterization and electrochemical properties of new functional polythiophenes

Synthetic Metals 160 (2010) 2681–2686

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Synthetic Metals journal homepage: www.elsevier.com/locate/synmet

Synthesis, characterization and electrochemical properties of new functional polythiophenes E. Salatelli a,∗ , L. Angiolini a , A. Brazzi a , M. Lanzi a , E. Scavetta b , D. Tonelli b a b

Dipartimento di Chimica Industriale e dei Materiali, Università di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy

a r t i c l e

i n f o

Article history: Received 28 January 2010 Received in revised form 21 July 2010 Accepted 25 October 2010 Available online 26 November 2010 Keywords: Conducting polymers Cyclic voltammetry Functional polythiophenes

a b s t r a c t Novel fully soluble polythiophene derivatives containing halogen or ester moieties at the end of a tetramethylenic side chain were synthesized using either the direct oxidative polymerization procedure of functionalized thiophene or the post polymerization functionalization of the preformed polymeric precursor. The structures of the polymers were characterized and their physical properties carefully ¯ n up to 30,550 g/mol) and thermostable products were investigated. High average molecular weights (M obtained. The absorption wavelength of the polymers in different solvents can be tuned up by varying the composition of solvent mixtures. Cyclic voltammetry measurements displayed good charge transport properties, strongly related to the kind of substituent linked to the side chain. © 2010 Elsevier B.V. All rights reserved.

1. Introduction In the recent years, inherently conducting polymers (ICP) such as polyaniline [1], poly(paraphenylene) [2] and polypirrole [3] have been extensively studied due to their remarkable electrical, optical and biological properties [4]. Among ICPs, polythiophene has received a particular attention although technological applications are limited because of its insolubility, due to high crystallinity, and, in consequence, poor processability. The introduction of substituents on the thiophene rings is probably the simplest way of tuning the chemical and physical properties of this class of polymers and many examples can be found in the literature. E.g., the introduction of linear alkyl side chain leads to the obtainment of soluble, easily filmable and processable poly(alkylthiophenes) (PATs) [5–7] while the employment of hydrophilic substituents yields watersoluble derivatives [8,9]. In addition, the incorporation of suitable functionalities into the polythiophenic backbone improves some properties and induces chemical changes which can have important effects on the structural and electronic properties of the final material. In this context, PAT derivatives functionalized with ester groups have been reported in early studies [10–13] demonstrating the important role played by this substituent for the increase of solubility and light absorption properties of the products. More-

∗ Corresponding author. Tel.: +39 51 2093685. E-mail address: [email protected] (E. Salatelli). 0379-6779/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2010.10.026

over, ␤-substituted polythiophenes ␻-functionalized with bromide groups can be very interesting and useful starting materials to obtain further ␤-substituted polymeric derivatives. In fact, the terminal bromide atom at the end of the alkyl side-chain can easily react with other functional groups leading, for example, to polythiophenes bearing side-chain carboxy acids, carboxy acid derivatives or amines [14]. The possibility to improve, modulate and modify the chromic properties of these PATs varying the functional group inserted in the side chain, leading to polymeric chemosensors acting as optical transducers towards specific trigger molecules, is very intriguing and makes these innovative materials very useful in systems based on their solvatochromic [15], ionochromic [16] or affinochromic [17] properties. To the light of these findings, aim of this work is the synthesis of two new PAT derivatives, namely poly[3-(4bromo)butylthiophene] (PT4Br) and poly[3-(4-butanoyloxy) butylthiophene] (PT4Bu), bearing, respectively, an halogen and an ester group at the end of a butylenic spacer (see Scheme 1). Both the above polymers were obtained by direct polymerization of the corresponding monomers using an optimized oxidative polymerization procedure, while PT4Bu was also prepared using an indirect route involving the post-functionalization of a polymeric precursor in order to find a more simple, quick, efficient and economically convenient polymerization procedure. The polymeric products were fully characterized by 1 H NMR, FT-IR and UV–vis spectroscopies, GPC, TGA and DSC techniques and also by means of cyclic voltammetry in order to evaluate their properties in terms of charge transport.

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O (CH2) 4 Br S

O

(CH2) 4 OC(CH2)2CH3

Na+ -OC(CH2)2CH3

T4Br

T4Bu

S

DMF

FeCl3 CCl4/CH3NO 2 FeCl3 CCl4/CH3NO2

PT4Bu2 (CH2) 4 Br S

O Na+ -OC(CH2)2CH3 DMF

O

(CH2) 4 OC(CH2) 2CH3

PT4Bu1

S

PT4Br Scheme 1. Synthetic pathways of PT4Br, PT4Bu1 and PT4Bu2.

2. Experimental 2.1. Measurements All reagents were purchased from Aldrich Chemical Co. and used without further purification when not otherwise mentioned. Solvents were purified by normal procedures, stored over molecular sieves and handled in a moisture-free atmosphere. 1 H NMR spectra of monomers and polymers were recorded at room temperature with a Varian Gemini 300 (300 MHz) or a Varian Mercury 400 (400 MHz) spectrometer using 5–10% solutions in CDCl3 and TMS as the internal standard. FT-IR of the monomers (pure liquids) and polymers (films) was carried out on KBr disks using a Perkin Elmer 1750 or Spectrum One spectrophotometer. UV–vis spectra in CHCl3 or CHCl3 /MeOH mixtures were carried out at 21 ◦ C on solutions prepared with spectroquality solvents at a constant polymer concentration of 7 × 10−5 mol l−1 in terms of one repeating unit, using a Perkin Elmer Lambda 19 spectrophotometer. Average molecular weights and polydispersity values of the polymers were determined by gel permeation chromatography (GPC) analysis in THF, using polystyrene standards for calibration, with an apparatus equipped with a HPLC pump Lab Flow 2000, a Rheodyne 7725i injector, a UV–vis detector Linear Instruments 200 operating at 254 nm, and a Phenomenex Phenogel mixed bed 5 ␮m MXM or MXL column. DSC thermal analyses were carried out on a TA Instruments 2920 operating under nitrogen, at a scan rate of 10 ◦ C/min. The reported thermal transition values refer to the second cycle of heating. Thermogravimetric measurements were carried out on a TA Instruments 2050 operating in oxidizing (air) atmosphere at a heating rate of 20 ◦ C/min to determine the decomposition temperature of the samples. Mass spectra were recorded on a Thermo Finnigan MAT 95 XP spectrometer. Cyclic voltammetry was performed with an Autolab PGSTAT100 (Ecochemie, Utrecht, The Netherlands) potentiostat/galvanostat interfaced with a PC under GPES software, with the aim of studying the charge/discharge behaviour of the synthesized polymers. All electrochemical tests were carried out in a single-compartment three-electrode cell, at room temperature, under N2 atmosphere. A 3 mm diameter glassy carbon (GC) disk electrode was used as the working electrode, an aqueous saturated calomel electrode (SCE) was the reference electrode, and a Pt wire was the auxiliary electrode. The working electrode was polished with an aqueous

alumina (Logitech) slurry of decreasing grain size (1 and 0.3 ␮m) on a polishing cloth. After each step the surface was rinsed with doubly distilled water. Finally the electrode was poured into a water ultrasonic bath for 5 min, to remove any trace of alumina. After the polishing treatment, 20 ␮l of a CHCl3 solution (about 2 mg ml−1 ) of the sample was dropped on the GC surface and air-dried. In such a way a thin film of the material under investigation was obtained on the GC surface. All the electrochemical experiments were carried out in CH3 CN (Aldrich, anhydrous, +99.8% pure, packaged under nitrogen) using 0.2 M tetrabutylammonium hexafluorophosphate (TBAPF6 , Fluka, puriss. ≥99%) as supporting electrolyte. 2.2. Monomers synthesis 2.2.1. 3-(4-Bromo)butylthiophene (T4Br) 3-[4-(-4-Methoxy)phenoxy]butylthiophene (1.85 g, 7.0 mmol), prepared according to Ref. [18], was reacted with HBr in acetic anhydride as reported [12] giving 0.56 g (37% yield) of T4Br. 1 H NMR (CDCl , ppm) ı 7.27 (d, 1H, H ), 6.94 (m, 2H, H and ␣ ␣ 3 H␤ ), 3.44 (t, 2H, –CH2 Br), 2.67 (t, 2H, thiophene–CH2 –), 2.00–1.68 (m, 4H, –CH2 –). 2.2.2. 3-(4-Butanoyloxy)butylthiophene (T4Bu) 0.56 g (2.6 mmol) of T4Br and 0.57 g (5.2 mmol) of sodium butyrate in 7 ml of anhydrous N,N-dimethylformamide (DMF) were reacted for 2 h at 90 ◦ C under stirring and inert atmosphere. The mixture was then poured into 10 ml of distilled water and extracted several times with n-hexane. The collected organic phases were dried (Na2 SO4 ), evaporated to dryness and the crude product submitted to column chromatography purification (SiO2 /n-hexane:dietylether, 9:1) giving 0.43 g (75% yield) of pure T4Bu. 1 H NMR (CDCl , ppm) ı 7.25 (d, 1H, H ), 6.95 (m, 2H, H and ␣ ␣ 3 H␤ ), 4.10 (t, 2H, –CH2 OCO–), 2.64 (t, 2H, thiophene–CH2 –), 2.23 (t, 2H, –CH2 CO–), 1.68 (m, 6H, –CH2 –), 0.95 (t, 3H, –CH3 ). Mass (m/z) relative intensity: 226 (37, M+ ). 2.3. Polymers synthesis 2.3.1. Poly[3-(4-bromo)butylthiophene] (PT4Br) A solution of 5.6 mmol of anhydrous FeCl3 in 6 ml of dry CH3 NO2 was dropped over 20 min in a solution of 1.7 mmol of T4Br in 20 ml of dry CCl4 . The mixture was stirred for 40 min at room temper-

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Table 1 Relevant data for the synthesized polymers. Sample PT4Br PT4Bu1 PT4Bu2 a b c d

Yield (%) c

75 69d 68c

¯ n (g/mol) M 29,500 30,400 30,550

¯ w /M ¯n M

DPa

Regioregularity (%)b

1.84 1.73 1.60

136 61 136

67 61 69

Average polymerization degree. Determined by 1 H NMR. Calculated as (gram of polymer/gram of monomer) × 100. Calculated as (gram of functionalized polymer/gram of starting polymer) × 100.

ature under a gentle flux of inert gas and then 50 ml of freshly distilled THF was added. After stirring for further 5 min, the mixture was transferred in a separatory funnel and added with 20 ml of CHCl3 . The solution was repeatedly washed with 2% aqueous HCl up to complete elimination of the ferric ion (aqueous extracts tested with aqueous 5% NH4 SCN till negative reaction), dried (Na2 SO4 ), filtered and evaporated to dryness. The crude polymer (0.325 g, 88% yield) was then fractionated by precipitation with methanol (100 ml) from a concentrated CHCl3 solution (5 ml) giving 0.277 g of pure PT4Br (75% yield). 1 H NMR (CDCl , ppm) ı 7.06, 7.03, 7.01 and 6.98 (4s, 1H, H ), 3 ␤ 3.45 (t, 2H, –CH2 Br), 2.80 and 2.55 (2bm, 2H, thiophene–CH2 –), 2.01–1.69 (m, 4H, –CH2 –).

extracted several times with CHCl3 . The collected organic phases were dried (Na2 SO4 ), filtered, evaporated to dryness giving 0.043 g (96% yield) of crude polymer. It was then dissolved in 10 ml of CHCl3 and slowly added, under stirring, to 100 ml of MeOH, filtered on a Teflon septum (0.45 ␮m pore size) and washed several times with methanol, yielding 0.18 mmol of fractionated polymer. The latter was finally dissolved in 5 ml of freshly distilled THF and the resulting solution dropped into 50 ml of MeOH. After filtration on a Teflon membrane (0.20 ␮m pore size) 0.14 mmol (0.031 g, 69% yield) of purified PT4Bu1 was collected. The 1 H NMR was the same as that of PT4Bu2.

2.3.2. Poly[3-(4-butanoyloxy)butylthiophene] (PT4Bu2) by direct route A solution of 5.6 mmol of anhydrous FeCl3 in 6 ml of dry CH3 NO2 was dropped over 20 min in a solution of 1.6 mmol of T4Bu in 20 ml of dry CCl4 . The mixture was stirred for 40 min at room temperature under a gentle flux of inert gas and then 50 ml of freshly distilled THF was added. After stirring for further 5 min, the mixture was transferred in a separatory funnel and added with 20 ml of CHCl3 . The solution was repeatedly washed with 2% aqueous HCl up to complete elimination of the ferric ion (aqueous extracts tested with aqueous 5% NH4 SCN till negative reaction), dried (Na2 SO4 ), filtered and evaporated to dryness. The crude polymer (0.330 g, 92% yield) was then fractionated by precipitation with methanol (100 ml) from a concentrated CHCl3 solution (10 ml) leading to 0.244 g of pure PT4Bu2 (68% yield). 1 H NMR (CDCl , ppm) ı 7.05, 7.02, 7.00 and 6.98 (4s, 1H, H ), 3 ␤ 4.10 (t, 2H, –CH2 OCO–), 2.82 and 2.58 (2bm, 2H, thiophene–CH2 –), 2.25 (t, 2H, –CH2 CO–), 1.69 (m, 6H, –CH2 –), 0.95 (t, 3H, –CH3 ).

Two different polymerization routes were followed for the synthesis of the ester-functionalized polythiophene PT4Bu (Scheme 1). Initially, the synthesis of PT4Bu was carried out through an indirect route, involving the exhaustive nucleophilic substitution by sodium butyrate of the bromine atom of PT4Br, prepared in turn by oxidative polymerization of 3-(4-bromo)butylthiophene. The second pathway was based on the direct polymerization of 3-(4butanoyloxy)butylthiophene, obtained by the same nucleophilic reaction conducted on the brominated monomer instead of its polymeric derivative. To the light of the substantially similar reaction yields obtained (Table 1), both the experimented pathways can be effectively applied for the obtainment of the ester-functionalized polymer. The direct route, leading to PT4Bu2, gives a polymer with similar molecular weight to PT4Bu1. However, the indirect route advantageously involves the synthesis of PT4Br, a very useful intermediate easily convertible to other ␻-functionalized polyalkylthiophenes with different features. In both cases, the adopted procedure was the oxidative polymerization via iron trichloride, the most common method for the generation of PATs [19,20]. In fact, this way is particularly simple, cost-effective and leads to the obtainment of polythiophene homopolymers or copolymers [21] with high molecular weights, appreciably polydispersity and regioregularity generally higher than 70% [22]. In order to afford highly purified polymers with

2.3.3. Poly[3-(4-butanoyloxy)butylthiophene] by indirect route (PT4Bu1) PT4Br (0.045 g, 0.2 mmol) and 0.079 g (0.7 mmol) of sodium butyrate were added to a 1:1 (v/v) mixture (20 ml) of anydrous THF/DMF and stirred at 60 ◦ C for 3 days under inert atmosphere. The reaction mixture was then poured into 150 ml of distilled water and

3. Results and discussion

Table 2 Relevant FT-IR frequencies (cm−1 ) for monomers and polymers. Assignment

T4Br

T4Bu

PT4Br

PT4Bu1

PT4Bu2

 C–H, thiophene, ␣ hydrogen  C–H, thiophene, ␤ hydrogen  CH3, antisymmetric  CH2, antisymmetric  CH2 , symmetric C O  C C, thiophene, antisymmetric  C C, thiophene, symmetric  C–O, antisymmetric  C–O, symmetric  C–H out of plane, 2, 3, 5 trisubstituted thiophenic ring  C–H out of plane, monosubstituted thiophenic ring  C–Br

3102 3047 – 2936 2857 – 1537 1457 – – – 772, 685 630, 559

3103 3050 2962 2936 2873 1734 1537 1458 1254 1180 – 774, 686 –

– 3055 – 2925 2855 – 1512 1457 – – 831 – 642, 560

– 3064 2958 2931 2871 1734 1514 1459 1253 1180 835 – –

– 3056 2961 2936 2873 1733 1514 1456 1254 1180 834 – –

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E. Salatelli et al. / Synthetic Metals 160 (2010) 2681–2686 Table 3 UV–vis max and max values of polymers and average conjugation length (nL )a in pure chloroform (A) and after methanol additions (B). Sample

max (A) (nm)

max (B)

nL (A)

nL (B)

PT4Br PT4Bu1 PT4Bu2

428 423 429

48 9 10

5 4 5

8 5 6

a

Fig. 1. 1 H NMR spectra in CDCl3 of T4Br, PT4Br and PT4Bu1. The inset shows the expanded integrated region of the spectrum related to the methylene group linked to thiophene ring.

narrow polydispersity, the crude polymeric samples were accurately fractionated using a CHCl3 /MeOH mixture (1:5, v/v), thus giving polymeric fractions that were completely soluble in various organic solvents such as chloroform, methylene chloride and THF, ¯ w /M ¯ n ) ranging in the 1.6–1.8 interval with a polydispersity index (M (Table 1). The regioregularity, determined by 1 H NMR analysis (see below) expressed in terms of HT-linked dyads was in the 61–69% range, in agreement with the values usually found with this polymerization procedure. The comparison of the FT-IR spectra of the monomers with the related polymers (see Table 2) suggests that the desired structures with good polymerization degrees and devoid of ␣–␤ and ␤–␤ linkages between thiophene rings were obtained. Moreover, no evident broad absorptions were observed in the 1390–1030 cm−1 range, proving the effectiveness of the adopted procedure of dedoping and purification of the polymers from residual FeCl3 . In Fig. 1 the 1 H NMR spectra of monomer T4Br, the corresponding polymer PT4Br and polymer PT4Bu1, obtained by post-polymerization functionalization of PT4Br, are reported. The relatively high molecular weights evaluated by GPC analysis are in agreement with the absence of resonances attributable to chain end groups. Moreover, the polymerization regioselectivity is confirmed by the integral ratio of the signals at 2.86 and 2.62 ppm, assigned to HT and HH–TT dyads, respectively [23], leading to the percent extent of regioregularity reported in Table 1. The comparison between PT4Br and PT4Bu1 spectra evidences the complete conversion of the halogenide into the ester functionality. In fact, the –CH2 Br triplet at 3.45 ppm is completely missing in

Calculated from Ref. [22].

the spectrum of PT4Bu1, which instead clearly shows the signals of the butanoyloxy functionality, i.e. –CH2 OCO– (4.10 ppm), –CH2 CO– (2.25 ppm) and –CH3 (0.95 ppm). The 1 H NMR spectrum of PT4Bu2 obtained by direct polymerization, not reported in Fig. 1, was identical to that of PT4Bu1 and inserted in Supplementary Information. It is however important to underline that to obtain a PT4Bu1 sample completely devoid of any residual trace of bromine functionality, the polymer was subjected to an accurate purification procedure involving the use of different solvent/non solvent systems, exploiting the quite different solubilities between the ester-functionalized polymer and its precursor. The thermal properties of the synthesized polymers were examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA in air of PT4Br shows an initial loss of halogenide group at approximatively 290 ◦ C, followed by the sidechain (at ca. 400 ◦ C) and finally the backbone decomposition at higher temperature (ca. 600 ◦ C). A more complex trend is followed by PTBu1 and PTBu2, starting to lose weight at 168 and 175 ◦ C, respectively. The DSC thermograms recorded during the heating process show a second-order transition (Tg ) centered at 19 ◦ C (PTBr), 16 ◦ C (PTBu1) and 24 ◦ C (PTBu2). No melting or crystallization peaks were observed, in agreement with the essentially amorphous character of this kind of polymers. The UV–vis absorptions of the polymers were measured in chloroform solution and after gradually increasing the additions of methanol (poor solvent) up to solute aggregation. In pure chloroform, the wavelengths of the absorption maxima related to the ␲–␲* electronic transition of thiophene ring, were nearly the same, in the 423–429 nm range (Table 3). A bathochromic shift (max ) was observed in the spectral profile of each polymer upon increasing the amount of poor solvent, indicating a progressive change from a fully solvated random conformational arrangement of the macromolecules to more ordered conformations involving increased main chain electronic conjugation originated by the presence to a larger extent of coplanar thiophene repeating units. The red shift was particularly evident for the brominated sample (Fig. 2) while for the ester-functionalized samples this effect was notably reduced, probably because of their more sterically crowded backbone hindering the possibility of generation of coplanar aromatic rings. A well defined isosbestic point is also evident in the spectra of PT4Br which suggests the presence in solution of two chromophoric species, the solvated, disordered, one and that possessing a progressively higher microaggregated ordered state [24]. This finding suggests that the bromide group plays an important role in controlling the side-chain mobility and, consequently, the rotational freedom of the polymeric chains. In the presence of methanol, an appreciable more planar backbone conformation and therefore a more extended conjugation length (nL ) is favoured. Indeed, the nL values in pure solvent (CHCl3 ), as evaluated using the Jiang formula [25], relating the number of conjugated thiophene rings to the frequency of the absorption maximum, are substantially the same for our polymeric samples, corresponding to 4 conjugated repeating units for PTBu1 and to 5 for PTBu2 and

E. Salatelli et al. / Synthetic Metals 160 (2010) 2681–2686

Fig. 2. UV–vis spectra of PT4Br in CHCl3 /CH3 OH mixtures (v:v): (a) pure CHCl3 , (b) 5:1, (c) 2:1, (d) 1:1, (e) 1:2, (f) 1:5.

PTBr (Table 3). Upon MeOH addition, a conformational rearrangement takes place leading to an increase in the number of coplanar thiophene rings. Based on the bathochromic shift, this increase can be estimated to be equal to only 1 ring for PT4Bu1 and PT4Bu2 but to 3 rings for PT4Br. Thus, this latter sample is therefore more prone to chromic transitions induced by surrounding physico-chemical changes (solvent polarity, temperature, concentration) than the ester-functionalized samples and can be more effectively employed as a chromic sensor in systems based on chemorecognition principles [26]. The first cyclic voltammetric curves recorded at GC electrodes coated with PT4Bu1 or PT4Br are reported in Fig. 3. The esterfunctionalized sample PT4Bu2 gave voltammetric signals as those recorded for PT4Bu1 (CV reported as Supplementary Information). In all cases, the first sweep was carried out on the material as it is, prior to the electrochemical study. The samples can be oxidatively doped, as demonstrated by cyclic voltammetry. In particular, PT4Bu1 turns to the electrically conductive state when an anodic potential of ca. +0.550 V is applied to the electrode, showing two clear anodic peaks at about 0.70 and 0.95 V vs. SCE whose cathodic counterpart, associated with the undoping process, is spread over a broad potential interval.

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The cyclic voltammogram of PT4Bu1 was stable and reproducible through repeated scannings (about 20 cycles), indicating a good reversibility of the charge/discharge process for this polymer, which is an important feature for a possible use of this polymer in the sensors field or as electroactive layer in organic cells. The dependence of the first anodic peak current on the square root of the potential scan rate was also investigated for PT4Bu1 and PT4Bu2. The plot reported for PT4Bu1, as Supplementary Information, results linear in the range of potential scan rate from 0.05 to 0.1 V s−1 thus confirming that the polymers charge process in diffusion controlled. However, the polymer was sensitive to overoxidation when the scan was carried out at a potential higher than +1.40 V, resulting in the depletion of the electrochemical activity of the sample. The effect of overoxidation is clearly evidenced in the subsequent potential scans (responses not shown). The value of the overoxidation potential is of sound relevance in view of potential applications for a given material. In the case of PT4Br, the p-doping potential is shifted to a higher potential by more than 200 mV with respect to that of the ester derivative. Moreover, the reversibility of the doping–dedoping process is poorer, as the p-doping potential shifts to more anodic potential and at the same time the material progressively loses its electroactivity, already at the second voltammetric cycle. It therefore appears that PT4Br does not display any electrochemical reversibility behaviour. Since most of the conductive polymers can be synthesized also by electrochemical methods the ester-functionalized polymer could be directly electrodeposited on the GC electrode and the extent of oxidation and the nature of the counterion easily controlled. In such a way the modified electrode could find application in the field of chemical or biochemical sensors due to its ability to mediate the electron flow [27].

4. Conclusions A new functional polythiophene derivative, namely poly[3(4-butanoyloxy)butylthiophene], can be prepared through two different, substantially equivalent, synthetic methods, by direct polymerization of ester-functionalized thiophene or by quantitative ester functionalization of the brominated polymeric precursor. The thermal and solvatochromic performances of the brominated polymeric sample appear improved with respect to those observed for the ester-functionalized samples, probably as a consequence of reduced steric requirements and more extended main chain electronic conjugation degree. The electrochemical characterization of polymers-coated GC surfaces indicates that the materials can be charged/discharged in the potential range 0.6–1.3 V, although the process is reversible and reproducible only for the ester functionalized derivatives. The possibility to obtain homogeneous, thick and self-consistent films of this ester-functionalized polymer, together with its low hysteresis showed during the charge–discharge processes, makes this material particularly suitable for application in electrical or electrooptical devices.

Acknowledgements Financial support from Consortium INSTM and PRIN 2007 (2007 WJMF2W) project is gratefully acknowledged.

Appendix A. Supplementary data Fig. 3. Cyclic voltammograms of PT4Bu1/GC and PT4Br/GC (first and second cycle) in CH3 CN containing 0.2 M TBAPF6 at 0.050 V s−1 potential scan rate. The switching potential is +1.40 V.

Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.synthmet.2010.10.026.

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