Synthesis and characterisation of electrical conducting polymers co polymers based on omega functionalised 3 alkylthiophenes 2

Chapter Syntheses and Characterisation of Electrically Conductive and Fluorescent Poly[3-( bromoalkyl)thiophenes] 1. Introduction 1.1 Conducting polythiophene Amongst the many families of electrically conductive materials, functionalised polythiophenes have always occupied an important position. Apart from their good electrical properties, processibility, environmental stability and amenity to wide-ranging potential technological applications, their optical properties [1], thermochromistic [2], piezochromistic [3], luminescence [4] behavior are all attracting increasing research interests. Chemical modification of monomeric building blocks in these conducting polymers allows for the structural control and tailoring of the respective polymer properties. In particular, pendant functionalisation offers an attractive possibility of developing materials that, in addition to particular polymer electronic properties, incorporate specific properties of the pendant functionality [5]. It was also reported that the semiconducting conjugated polymers exhibit fluorescent characteristics, which made them potential materials for application as polymer light-emitting diodes (PLEDs) [6]. 32 1.2 Functionalised poly(3-alkylthiophene) A variety of chemically modified structures have been developed through substitution on the thiophene ring [7]. Attachment of pendant alkyl chains of suitable lengths at the 3-position of thiophene has been shown to afford a series of solvent processible and fusible poly(3-alkylthiophenes) [8]. Amongst the many poly(3-alkylthiophenes) formed, poly[3-( -substituted alkyl)thiophene] is of particular interest. It is anticipated that the functionalisation of the alkyl pendant chain with reactive -moieties in polythiophenes will produce novel kinds of practically useful polymers. These polymers would lend themselves to postpolymerisation treatment processes, particularly in the generation of electrically conductive composite materials for anti-static applications. Previous efforts in this direction include poly[3-( -hydroxyalkyl)thiophene] of different chain lengths [9], which demonstrated comparable conductivity to those of poly(3alkylthiophene) upon doping but reduced solubility due to the hydroxyl moieties. It has also been proven that the hydroxyl group is still an active functional group after polymerisation [10]. This creates the possibility of post-polymerisation treatment to generate new material. As the first step of developing new material that graft commodity polymer and conductive polymer, this chapter report the findings on the preparation and properties of functionalised polythiophene with -bromoalkyl substituents [viz. Poly(Th-Cn-Br) n=4, 6, 8, 10, 12]. These polymers are anticipated to be amenable to facile synthetic transformation to a range of other functional materials via the reactive halide moiety. 33 The syntheses of the monomeric 3-( -bromoalkyl)thiophenes have been reported briefly by Bäuerle et al. [11]. In this work, a straightforward FeCl3 polymerisation approach was utilised in order for preliminary data on the polymer properties to be evaluated. These functionalised polymers themselves may also be applicable in the field of sensors, microelectronic devices and/or electro-catalysis [12]. 34 1.3 Scope of the work in this chapter 1) To synthesise the following monomers: 3-( -bromobutyl) thiophene (THC4Br) 3-( -bromohexyl) thiophene (THC6Br) 3-( -bromooctyl) thiophene (THC8Br) 3-( -bromodecyl) thiophene (THC10Br) 3-( -bromododecyl) thiophene (THC12Br) 2) To characterise all monomers synthesised by structural techniques using analytical instruments such as Fourier Transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), mass spectrometry (MS) and elemental analysis. 3) To effect chemical polymerisation of the monomers synthesised by FeCl3 oxidative method to form the following polymers: (CH2)nBr [ S ]m n = pTHC4Br pTHC6Br pTHC8Br 10 pTHC10Br 4) 12 pTHC12Br To characterise all polymers formed by structural techniques using analytical instruments such as Fourier Transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC) and elemental analysis. 5) To study the conductivity of the polymers and the effects of dopants on conductivity. 35 6) To study the electro-optical properties of the polymers through ultraviolet absorption spectrometry (UV) and fluorescence emission spectrometry. 7) To determine the thermal properties of the polymers by thermogravimetry. 8) To analyse the surface characteristics of the polymers by X-ray photoelectron spectroscopy (XPS). 9) To test the possibility of effecting functional group transformation via the reactive -bromo moiety. 36 2. Experiment 2.1 Syntheses of monomers 2.1.1 Overview Monomers were synthesised in accordance to the method of Bäuerle et al. [11], which is depicted in Scheme 2.1. i Br(CH2)nBr + HO Br(CH2)nO OCH3 OCH3 (I) ii (CH2)nO S OCH3 iii Br BrMg(CH2)nO (IV) OCH3 (II) + S (III) iv (CH2)nBr S (V) Scheme 2.1 The n = 4, 6, 8, 10, 12 Monomer synthesis. Reagents and conditions: (i) KOH/MeOH, acetone, reflux; (ii) Mg, I2, anhydrous ether, reflux; (iii) Ni(dppp)Cl2, anhydrous Ether; (iv) HBr/Ac2O, 100 C -(p-methoxyphenoxy)alkyl bromides, easily prepared from , - dihaloalkanes and hydroquinone monomethyl ether (HCM), react readily with magnesium to give the corresponding Grignard compounds. The -(p- methoxyphenoxy)alkyl bromides (n = 4, 6, 8, 10, 12) undergo nearly quantitative Grignard reaction to afford its alkylmagnesium bromides Grignard reagent (n = 4, 6, 8, 10, 12). The nickel-catalysed Grignard coupling of 3-bromothiophene and 37 the alkyl magnesium bromides (n = 4, 6, 8, 10, 12) (0.1 – mol % Ni(dppp)Cl2 as catalyst in refluxing ether or THF*) leads to the terminally protected 3-[ -(pmethoxyphenoxy)alkyl] thiophenes, which after a single recrystallisation, can be obtained in 63 – 81% yield as a colourless, analytically pure solid. Of the numerous ether cleavage methods, that with hydrogen halide/acetic anhydride proved to be best suited for the cleavage of the HCM protecting group in 3-[ -(p-methoxyphenoxy)alkyl] thiophenes. These 3-substituted thiophenes were thus converted directly into 3-( -bromoalkyl)thiophenes. The best yields were obtained using HBr/Ac2O at 100 C/20-25 hr for 3-( -bromoalkyl) thiophenes. After separation of the simultaneously formed hydroquinone followed by chromatographic and distillative purification, halides were obtained as analytically pure compounds in 51 –76% yield. In an attempt to achieve a higher yield for the key monomer, the pmethoxyphenoxy protecting groups were replaced with p-methylphenoxy and pt butylphenoxy protecting groups for , -dibromodecane. The same procedure was followed except HCM was replaced with p-methylphenol and p-tbutylphenol respectively in the first step. The yields were compared. * For n = 8, 10, 12, THF was used due to the decreasing solubility of the alkymagnesium Grignard reagent in ether which caused practical difficulties in the transferring process. 38 2.2 Polymerisation The following polymers were formed: (CH2)nBr [ S ]m n = pTHC4 Br pTHC6Br pTHC8 Br 10 pTHC10 Br 12 pTHC12 Br Polymerisation was carried out using the method of Casa et al. [13]. Poly[3-( bromoalkyl)thiophenes] were obtained by dropwise addition of FeCl3 in nitromethane to a solution of the monomer in carbon tetrachloride. Since FeCl3 is insoluble in CCl4, FeCl3 (the active state of the oxidant) gradually precipitates and reacts with the monomer. This is a uniformed polymerisation method with the formation of a very fine powder suspension of the polymers. The as-synthesised polymers, i.e. complexed (doped) with FeCl3, could be completely changed to the neutral (undoped) state by soxhlet extraction with methanol and acetone in turn. The dedoping was evidenced from the disappearance of characteristic doping bands in the FT-IR spectrum, at 1150 cm-1 and 1350 cm-1. As a comparison, the method of Sugimoto et al. [14], the usual method for oxidative polymerisation using a suspension of FeCl3 in dry chloroform was also used for 3-( -bromohexyl)thiophene. This was effected by either rapid addition of the monomer solution in one portion (PBHT2) or adding the monomer solution dropwise generated the polymers (PBHT3). 39 3. Results and Discussion 3.1 Experiments on different protecting group According to the method of Bäuerle et al. (scheme 2.1), the p-methoxyphenoxy group was used as a protecting group and was later cleaved using hydrogen halide/acetic anhydride to afford the monomer. One of the by-products of the cleavage reaction was found to be 3-[ -(p-phenoxy)alkyl] thiophenes, which indicated that cleavage could also occur on the methoxy group. In the hope of eliminating this side reaction, p-methylphenoxy and p-tbutylphenoxy protecting groups were tested. It was found that the yields of the monomers were 32% and 20% respectively for these two protecting groups. The lower yield indicated that the presence of the methoxy group did help the cleavage of the protecting group in the original reaction. The electron donating effect of the methoxy group makes the protecting group electron rich, hence function as a better leaving group under acidic conditions. Replacing this methoxy group with methyl or p-tbutylphenoxy group could not compensate for this electron donating effect thus the yield was lower, even though the side reaction was eliminated. 40 -(p-methoxyphenoxy)butyl bromides 1H NMR (300MHz, CDCl3/TMS): =6.82-6.84 (d, 4H), 3.90-3.94 (t, 2H), 3.80(s, 3H), 3.49-3.51 (t, 2H), 2.01-2.11(m, 2H), 1.89-1.98(m, 2H), 1.51-1.61(m, 2H). -(p-methoxyphenoxy)hexyl bromides 1H NMR (300MHz, CDCl3/TMS): =6.83-6.85 (d, 4H), 3.91-3.95 (t, 2H), 3.81(s, 3H), 3.49-3.51 (t, 2H), 2.02-2.12(m, 2H), 1.90-1.99(m, 2H), 1.45-1.55(m, 6H). -(p-methoxyphenoxy)octyl bromides 1H NMR (300MHz, CDCl3/TMS): =6.81-6.83 (d, 4H), 3.92-3.95 (t, 2H), 3.78(s, 3H), 3.48-3.50 (t, 2H), 2.0-2.10(m, 2H), 1.88-1.97(m, 2H), 1.32-1.56(m, 10H). -(p-methoxyphenoxy)decyl bromides 1H NMR (300MHz, CDCl3/TMS): =6.83-6.84 (d, 4H), 3.89-3.94 (t, 2H), 3.80(s, 3H), 3.50-3.52 (t, 2H), 2.02-2.12(m, 2H), 1.90-2.0(m, 2H), 1.50-1.55 (m, 2H), 1.25-1.50(m, 12H). -(p-methoxyphenoxy)dodecyl bromides 1H NMR (300MHz, CDCl3/TMS): =6.81-6.83 (d, 4H), 3.90-3.95 (t, 2H), 3.81(s, 3H), 3.49-3.51 (t, 2H), 2.01-2.11(m, 2H), 1.90-1.99(m, 2H), 1.50-1.55 (m, 2H), 1.24-1.49(m, 20H). 62 Table 2.5 Percentage yields of Br-(CH2)n-OPhOMe and their melting points Br-(CH2)n-OphOMe n 10 12 (2) Yield (%) (with respect to HMC consumed) 75 80 70 63 83 Empirical M.p. ( C) Literature M.p. ( C) 42-44 47-49 54-56 59-60 62-64 42-43 46-47 52-53 58-59 64-65 -(p-methylphenoxy)decyl bromide. Potassium hydroxide (1.2 mole) in methanol (200 ml) was added to p-methylphenol (1 mol) in MeOH (50 ml) and the resulting solution was added dropwise in 90 to , - dibromodecane (2 mole) in acetone (400 ml). The mixture was refluxed for hr, concentrated and diluted with water. The organic layer was taken up in ether, and the ethereal extract was filtered from , -dimethoxyphenoxy alkane, washed with dilute sodium hydroxide and water, dried and distilled, giving recovered , -dibromodecane and -(p-methylphenoxy)decyl bromide. H NMR (300MHz, CDCl3/TMS): =7.25-7.26 (m, 2H), 6.92-6.94 (m, 2H), 3.90- 3.94 (t, 2H), 3.38-3.42 (t, 2H), 2.28 (s, 3H), 1.81-1.91(m, 2H), 1.71-1.78(m, 2H), 1.25-1.46(m, 8H). -(p-tbutylphenoxy)decyl bromide. (3) Potassium hydroxide (1.2 mole) in methanol (200 ml) was added to pt butylphenol (1 mol) in MeOH (50 ml) and the resulting solution was added 63 dropwise in 90 to , -dibromodecane (2 mole) in acetone (400 ml). The mixture was refluxed for hr, concentrated and diluted with water. The organic phase was taken up in ether, and the ethereal extract was filtered from , -dimethoxyphenoxy alkane, washed with dilute sodium hydroxide and water, dried and distilled, giving recovered , -dibromodecane and - (p-tbutylphenoxy)decyl bromide. H NMR (300MHz, CDCl3/TMS): =7.28-7.31 (m, 2H), 6.82-6.85 (m, 2H), 3.92- 3.96 (t, 2H), 3.39-3.43 (t, 2H), 1.76-1.86(m, 2H), 1.66-1.73(m, 2H), 1.25-1.46(m, 8H), 1.30 (s, 9H) (4) General procedure for the synthesis of 3-[ -(p- methoxyphenoxy)alkyl]thiophenes: -(p-methoxyphenoxy)alkyl bromides in 40 ml of anhydrous ether (THF for n=8, 10, 12) was added under inert atmosphere to magnesium turnings (0.15 mol) in 15 ml of ether, the reaction mixture was then refluxed for 5-6 hr. The Grignard solution of II was subsequently transferred via cannula to a second apparatus and added dropwise at C to Ni(dppp)Cl2 (0.1 mol%) and 3bromidethiophene (0.106 mol) over hr. The reaction mixture was refluxed for 12-15 hr before being hydrolysed by 40 ml of saturated NH4Cl solution and 150 ml of ice water followed by extraction with several portions of ether. Washing to neutrality and drying of the combined organic phases and 64 removal of the solvent in vacuum afforded a yellowish-white solid, which was recrystallised from n-hexane and methanol. Subsequent purification by silica gel chromatographic method with hexane and ethyl acetate as solvent afforded analytically pure IV. Table 1.6 depicts the results of this reaction. 3-[ -(p-methoxyphenoxy)butyl]thiophenes 1H NMR (300MHz, CDCl3/TMS): =7.24-7.26 (m, 1H), 6.92-6.96 (m, 2H), 6.81-6.84 (d, 4H), 3.92-3.96 (t, 2H), 3.80 (s, 3H), 2.70-2.73 (t, 2H), 1.75-1.86(m, 4H). MS(EI, m/e, %intensity): 262 (M+, 90%) 3-[ -(p-methoxyphenoxy)hexyl]thiophenes 1H NMR (300MHz, CDCl3/TMS): =7.23-7.26 (m, 1H), 6.91-6.95 (m, 2H), 6.80-6.83 (d, 4H), 3.93-3.97 (t, 2H), 3.81 (s, 3H), 2.70-2.73 (t, 2H), 1.61-1.86(m, 4H), 1.39-1.60 (m, 4H). MS(EI, m/e, %intensity): 290 (M+, 90%) 3-[ -(p-methoxyphenoxy)octyl]thiophenes 1H NMR (300MHz, CDCl3/TMS): =7.24-7.26 (m, 1H), 6.92-6.95 (m, 2H), 6.81-6.84 (d, 4H), 3.92-3.97 (t, 2H), 3.81 (s, 3H), 2.71-2.74 (t, 2H), 1.60-1.87(m, 4H), 1.34-1.58 (m, 8H). MS(EI, m/e, %intensity): 318 (M+, 90%) 3-[ -(p-methoxyphenoxy)decyl]thiophenes 1H NMR (300MHz, CDCl3/TMS): =7.23-7.26 (m, 1H), 6.91-6.95 (m, 2H), 6.80-6.83 (d, 4H), 3.93-3.97 (t, 2H), 65 3.81 (s, 3H), 2.70-2.73 (t, 2H), 1.51-1.78(m, 6H), 1.29-1.50 (m, 12H). MS(EI, m/e, %intensity): 346 (M+, 90%) 3-[ -(p-methoxyphenoxy)dodecyl]thiophenes CDCl3/TMS): H NMR (300MHz, =7.23-7.26 (m, 1H), 6.91-6.95 (m, 2H), 6.80-6.83 (d, 4H), 3.93- 3.97 (t, 2H), 3.81 (s, 3H), 2.70-2.73 (t, 2H), 1.51-1.78(m, 4H), 1.29-1.50 (m, 16H). MS(EI, m/e, %intensity): 374 (M+, 90%) Table2.6 Percentage yields of 3-[ -(p-methoxyphenoxy)alkyl]thiophenes and their melting points n 10 12 3-[ -(p-methoxyphenoxy)alkyl]thiophenes Yield (%) Empirical M.p. ( C) Literature M.p. ( C) 81 33-35 34-35 75 40-41 41-42 68 46-48 47-48 63 55-56 53-54 70 59-61 61-62 (5) 3-[ -(p-methylphenoxy)decyl]thiophene. -(p-methylphenoxy)decyl bromide (0.125 mol) in 40 ml of anhydrous ether was added under inert atmosphere to magnesium turnings (0.15 mol) in 15 ml of ether. The reaction mixture was then refluxed for 5-6 hr. The resulting Grignard solution was subsequently transferred using a cannula to another RBF and added dropwise at C to Ni(dppp)Cl2 (0.1 mol%) and 3bromothiophene (0.106 mol) in hr. The reaction mixture was refluxed for 12-15 hr before being hydrolysed by 40 ml of saturated NH4Cl solution and 66 150 ml of ice water. This is then followed by extraction with several portions of ether. Washing to neutrality and drying of the combined organic phases and removal of the solvent in vacuum afforded a yellowish-white solid, which was recrystallized from n-hexane and methanol. Further purification was carried out using silica gel chromatographic method with hexane and ethyl acetate as solvents to afford analytically pure 3-[ -(p-methylphenoxy)decyl]thiophene. H NMR (300MHz, CDCl3/TMS): =7.24-7.26 (m, 1H), 7.07-7.11 (m, 2H), 6.92- 6.96 (m, 2H), 6.81-6.84 (m, 2H), 3.92-3.96 (t, 2H), 3.62-3.67 (t, 2H), 2.30 (s, 3H), 1.73-1.81(m, 2H), 1.62-1.67(m, 2H), 1.25-1.46(m, 8H). (6) 3-[ -(p-tbutylephenoxy)decyl]thiophene. -(p-tbutylphenoxy)decyl bromide (0.125 mol) in 40 ml of anhydrous ether was added under inert atmosphere to magnesium turnings (0.15 mol) in 15 ml of ether. The reaction mixture was then refluxed for 5-6 hr. The resulting Grignard solution was subsequently transferred using a cannula to another RBF and added dropwise at C to Ni(dppp)Cl2 (0.1 mol%) and 3bromothiophene (0.106 mol) in hr. The reaction mixture was refluxed for 12-15 hr before being hydrolysed by 40 ml of saturated NH4Cl solution and 150 ml of ice water. This is then followed by extraction with several portions of ether. Washing to neutrality and drying of the combined organic phases and removal of the solvent in vacuum afforded a yellowish-white solid, which was recrystallised from n-hexane and methanol. Further purification was carried 67 out using silica gel chromatographic method with hexane and ethyl acetate as solvents to afford analytically pure 3-[ -(p-tbutylephenoxy)decyl]thiophene. H NMR (300MHz, CDCl3/TMS): =7.22-7.24 (m, 1H), 7.00-7.09 (m, 2H), 6.90- 6.94 (m, 2H), 6.79-6.82 (m, 2H), 3.89-3.95 (t, 2H), 3.60-3.64 (t, 2H), 1.711.79(m, 2H), 1.60-1.66(m, 2H), 1.32-1.48(m, 8H), 1.28 (s, 9H). (7) General procedure for the synthesis of 3-( -bromoalkyl)thiophene From 3-[ -(p-methoxyphenoxy)alkyl] thiophenes. A mixture of HBr (48%; 0.12 mol) and acetic anhydride (0.198 mol) was added under inert atmosphere to 3-[ -(p-methoxyphenoxy)alkyl] thiophenes (0.02 mol) and the reaction mixture was heated at 100 C for 20-25 hr. After dilution with water, the mixture was extracted several times with ether and the combined organic phases were washed to neutrality with saturated NaHCO3 solution. Drying of the organic phase and removal of the solvent afforded yellow-brown oil, from which hydroquinone was precipitated by addition of an n-hexane/ether mixture. The solution was then filtered, transferred to a short silica gel column and eluted with hexane. Removal of the solvent gave 3-( - bromoalkyl)thiophene. Further purification by Kugelrohr distillation (n=4, 6) or other chromatographic methods afforded an analytically pure, colorless oil. Table 2.7 depicts the results of this reaction. 68 3-( -bromodecyl)thiophene From 3-[ -(p-methylphenoxy)decyl]thiophene or 3[ -(p-tbutylephenoxy)decyl]thiophene. The same procedure as above, with the exception of the starting material, instead of 3-[ -(p-methoxyphenoxy)alkyl] thiophenes, t 3-[ -(p-methylphenoxy)decyl]thiophene or 3-[ -(p- butylephenoxy)decyl]thiophene was used. 3-( -bromobutyl)thiophene 1H NMR (300MHz, CDCl3/TMS): =7.22-7.25 (m, 1H), 6.92-6.93 (m, 2H), 3.37-3.42 (t, 2H), 2.59-2.64 (t, 2H), 1.70-1.89 (m, 4H). MS(EI, m/e, %intensity): 218 (M+, 40%), 220 (M+2, 40%). IR (cm-1): 3100, 3055, 2934, 2856, 1535, 1440, 1248, 1078, 774, 677, 553. Elemental Analysis: Calculated for {C8H11SBr} C: 43.8, H: 5.02, S: 14.6, Br: 36.5. Found: C: 45.6, H: 4.99 S: 15.2, Br: 34.2. 3-( -bromohexyl)thiophene 1H NMR (300MHz, CDCl3/TMS): =7.22-7.26 (m, 1H), 6.93-6.94 (m, 2H), 3.36-3.42 (t, 2H), 2.59-2.63 (t, 2H), 1.85-1.95 (m, 2H), 1.67-1.78 (m, 2H), 1.35-1.60 (m, 2H). MS(EI, m/e, %intensity): 246 (M+, 70%), 248 (M+2, 70%). IR (cm-1): 3108, 3059, 2938, 2855, 1540, 1445, 1218, 1078, 767, 678, 559. Elemental Analysis: Calculated for {C10H15SBr} C: 48.6, H: 6.08, S: 13.0, Br: 32.3. Found: C: 50.3, H: 6.20, S: 13.4, Br: 30.1. 3-( -bromooctyl)thiophene 1H NMR for (300MHz, CDCl3/TMS): =7.23-7.25 (m, 1H), 6.92-6.93 (m, 2H), 3.37-3.42 (t, 2H), 2.60-2.64 (t, 2H), 1.80-1.89 (m, 2H), 1.60-1.72 (m, 2H), 1.25-1.42 (m, 8H). MS(EI, m/e, %intensity): 274 (M+, 69 90%), 276 (M+2, 90%). IR (cm-1): 3102, 3057, 2934, 2858, 1537, 1448, 1220, 1076, 774, 675, 552. Elemental Analysis: Calculated for {C12H19SBr} C: 52.4, H: 6.91, S: 11.6, Br: 29.1. Found: C: 53.7, H: 7.18, S: 12.0, Br: 27.1. 3-( -bromodecyl)thiophene 1H NMR (300MHz, CDCl3/TMS): =7.22-7.26 (m, 1H), 6.92-6.94 (m, 2H), 3.37-3.43 (t, 2H), 2.59-2.64 (t, 2H), 1.81-1.90 (m, 2H), 1.61-1.72 (m, 2H), 1.25-1.42 (m, 12H). MS(EI, m/e, %intensity): 302 (M+, 75%), 304 (M+2, 75%). IR (cm-1): 3110, 2926, 2848, 1545, 1448, 1246, 1042, 761, 675, 566. Elemental Analysis: Calculated for {C14H23SBr} C: 55.5, H: 7.59, S: 10.6, Br: 26.4. Found: C: 55.2, H: 8.05, S: 9.74, Br: 27.0. Yield: 68% (from 3-[ -(p-methoxyphenoxy)decyl]thiophenes) 32% (from 3-[ -(p-methylphenoxy)decyl]thiophene) 20% (from 3-[ -(p-tbutylephenoxy)decyl]thiophene) 3-( -bromododecyl)thiophene 1H NMR (300MHz, CDCl3/TMS): =7.22-7.25 (m, 1H), 6.91-6.93 (m, 2H), 3.38-3.42 (t, 2H), 2.59-2.64 (t, 2H), 1.80-1.89 (m, 2H), 1.61-1.73 (m, 2H), 1.26-1.44 (m, 20H). MS(EI, m/e, %intensity): 330 (M+, 50%), 332 (M+2, 50%). IR (cm-1): 3110, 2928, 2845, 1542, 1454, 1220, 1088, 768, 643, 566. Elemental Analysis: Calculated for {C16H27SBr} C: 58.0, H: 8.16, S: 9.67, Br: 24.1. Found: C: 59.8, H: 8.45, S: 9.08, Br: 22.7. 70 Table2.7 Percentage yields of 3-( -bromoalkyl)thiophenes and their boiling points n 10 12 3-( -bromoalkyl)thiophene Yield (%) Empirical B.p. ( C) at 10-3 torr 64 55 75 75 70 90 68 108 63 120 Literature B.p. ( C) at 10-3 torr 60-65 80 90 105 120 (8) Poly[3-( -bromoalkyl)thiophenes] by the FeCl3 Route. A solution of anhydrous FeCl3 (17 mmol) in 16 ml of MeNO2 was added dropwise in 20 to a solution of poly[3-( -bromoalkyl)thiophenes] in 49 ml of CCl4. The reaction mixture was stirred for 40 min. and then poured into MeOH. The black solid was filtered and soxhlet-extracted with methanol and acetone to afford the polymer. The neutral polymers obtained were used for analytical purpose. All polymers obtained were in the form of black powder and could be dissolved totally (pTHC4Br, pTHC6Br and pTHC8Br) or partially (pTHC10Br and pTHC12Br) in common solvents like CHCl3, benzene and THF. Table 2.8 depicts percentage yield of this reaction. poly-[3-( -bromobutyl)thiophene] 1H NMR (300MHz, CDCl3/TMS): =6.95- 7.05 (m, 1H), 3.38-3.65 (t, 2H), 2.95(b, 1.4H), 2.67 (b, 0.6H), 1.80-2.1 (m, 4H), IR (cm-1): 3054, 3001, 2926, 2856, 1435, 1242, 814, 723, 635, 546. Elemental 71 Analysis: Calculated for {C8H9SBr} C: 44.3, H: 4.15, S: 14.8, Br: 36.8. Found: C: 48.0, H: 4.59, S: 15.8, Br: 31.6. poly-[3-( -bromohexyl)thiophene] 1H NMR (300MHz, CDCl3/TMS): =6.93- 7.02 (m, 1H), 3.36-3.48 (t, 2H), 2.85 (b, 1.5H), 2.60 (b, 0.5H), 1.85-1.95 (m, 2H), 1.67-1.80 (m, 2H), 1.35-1.60 (m, 6H). IR (cm-1): 3058, 3010, 2925, 2854, 1445, 1258, 829, 728, 639, 556. Elemental Analysis: Calculated for {C10H13SBr} C: 49.0, H: 5.31, S: 13.1, Br: 32.6. Found: C: 49.7, H: 5.67, S: 13.2, Br: 31.4. poly-[3-( -bromooctyl)thiophene] 1H NMR for (300MHz, CDCl3/TMS): =6.92-7.03(m, 1H), 3.37-3.42 (t, 2H), 2.81 (b, 1.9H), 2.58 (b, 0.1H), 1.82-1.95 (m, 2H), 1.65-1.82 (m, 4H), 1.45-1.58 (m, 10H). IR (cm-1): 3056, 3006, 2921, 2849, 1445, 1201, 827, 715, 638, 555. Elemental Analysis: Calculated for {C12H17SBr} C: 52.8, H: 6.23, S: 11.7, Br: 29.3. Found: C: 54.2, H: 6.59, S: 12.1, Br: 27.1. poly[3-( -bromodecyl)thiophene] 1H NMR (300MHz, CDCl3/TMS): =6.94- 7.04 (m, 1H), 3.37-3.43 (t, 2H), 2.83 (b, 1.2H), 2.59 (b, 0.8H), 1.81-1.90 (m, 2H), 1.51-1.82 (m, 5H), 1.25-1.42 (m, 12H). IR (cm-1): 3056, 3004, 2924, 2851, 1460, 1260, 828, 720, 643, 581. Elemental Analysis: Calculated for {C14H23SBr} C: 55.8, H: 6.98, S: 10.6, Br: 26.6. Found: C: 57.6, H: 7.18, S: 11.2, Br: 24.0. 72 poly-[3-( -bromododecyl)thiophene] H NMR (300MHz, CDCl3/TMS): =6.91-7.01(m, 1H), 3.38-3.42 (t, 2H), 2.82 (b, 1.2H), 2.56 (b, 0.8H), 1.80-1.89 (m, 2H), 1.61-1.73 (m, 2H), 1.26-1.44 (m, 20H). IR (cm-1): 3054, 3001, 2922, 2849, 1459, 1251, 820, 719, 643, 580. Elemental Analysis: Calculated for {C16H27SBr} C: 58.4, H: 7.60, S: 9.73, Br: 24.3. Found: C: 59.6, H: 7.94, S: 10.2, Br: 22.2. Table 2.8 Percentage yields of poly-3-( -bromoalkyl)thiophenes Poly-3-( -bromoalkyl)thiophenes N Yield (%) 78 67 80 10 65 12 73 (9) Doping with Iodine. 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Chem., 75, 1971, 991. 77 [...]... 3. 81(s, 3H), 3. 49 -3. 51 (t, 2H), 2. 02- 2. 12( m, 2H), 1.90-1.99(m, 2H), 1.45-1.55(m, 6H) -(p-methoxyphenoxy)octyl bromides 1H NMR (30 0MHz, CDCl3/TMS): =6.81-6. 83 (d, 4H), 3. 92 -3. 95 (t, 2H), 3. 78(s, 3H), 3. 48 -3. 50 (t, 2H), 2. 0 -2. 10(m, 2H), 1.88-1.97(m, 2H), 1 . 32 -1.56(m, 10H) -(p-methoxyphenoxy)decyl bromides 1H NMR (30 0MHz, CDCl3/TMS): =6. 83- 6.84 (d, 4H), 3. 89 -3. 94 (t, 2H), 3. 80(s, 3H), 3. 50 -3. 52 (t, 2H), 2. 02- 2. 12( m,... in polymers with lower solubility Table 2. 1 Polymer Summarised data of polymers formed GPC results Conductivity DPn pTHC4Br pTHC6Br pTHC8Br pTHC10Br pTHC12Br PHT PBHT2 PBHT3 Mn PDI 57 82 93 73 90 138 95 92 12 ,30 0 19,900 25 ,20 0 22 ,000 29 ,400 23 , 100 23 , 400 22 ,600 1.8 2. 0 1.8 2. 0 1.7 2. 7 1.9 2. 0 I2 doped (Scm-1) 4.7 7.9 10.4 8.4 7.5 9 .3 8 .2 7.9 HT dyads HH dyads % % 68 73 87 62 60 71 70 68 32 27 13 38... 2H), 2. 02- 2. 12( m, 2H), 1.90 -2. 0(m, 2H), 1.50-1.55 (m, 2H), 1 .25 -1.50(m, 12H) -(p-methoxyphenoxy)dodecyl bromides 1H NMR (30 0MHz, CDCl3/TMS): =6.81-6. 83 (d, 4H), 3. 90 -3. 95 (t, 2H), 3. 81(s, 3H), 3. 49 -3. 51 (t, 2H), 2. 01 -2. 11(m, 2H), 1.90-1.99(m, 2H), 1.50-1.55 (m, 2H), 1 .24 -1.49(m, 20 H) 62 Table 2. 5 Percentage yields of Br-(CH2)n-OPhOMe and their melting points Br-(CH2)n-OphOMe n 4 6 8 10 12 (2) Yield... %intensity): 26 2 (M+, 90%) 3- [ -(p-methoxyphenoxy)hexyl]thiophenes 1H NMR (30 0MHz, CDCl3/TMS): =7. 23 - 7 .26 (m, 1H), 6.91-6.95 (m, 2H), 6.80-6. 83 (d, 4H), 3. 93- 3.97 (t, 2H), 3. 81 (s, 3H), 2. 70 -2. 73 (t, 2H), 1.61-1.86(m, 4H), 1 .39 -1.60 (m, 4H) MS(EI, m/e, %intensity): 29 0 (M+, 90%) 3- [ -(p-methoxyphenoxy)octyl]thiophenes 1H NMR (30 0MHz, CDCl3/TMS): =7 .24 -7 .26 (m, 1H), 6. 92- 6.95 (m, 2H), 6.81-6.84 (d, 4H), 3. 92 -3. 97... 4H), 3. 92 -3. 97 (t, 2H), 3. 81 (s, 3H), 2. 71 -2. 74 (t, 2H), 1.60-1.87(m, 4H), 1 .34 -1.58 (m, 8H) MS(EI, m/e, %intensity): 31 8 (M+, 90%) 3- [ -(p-methoxyphenoxy)decyl]thiophenes 1H NMR (30 0MHz, CDCl3/TMS): =7. 23 - 7 .26 (m, 1H), 6.91-6.95 (m, 2H), 6.80-6. 83 (d, 4H), 3. 93- 3.97 (t, 2H), 65 3. 81 (s, 3H), 2. 70 -2. 73 (t, 2H), 1.51-1.78(m, 6H), 1 .29 -1.50 (m, 12H) MS(EI, m/e, %intensity): 34 6 (M+, 90%) 3- [ -(p-methoxyphenoxy)dodecyl]thiophenes... hydroxide and water, dried and distilled, giving recovered , -dibromobutane and -(p- methoxyphenoxy)butyl bromide 61 -(p-methoxyphenoxy)butyl bromides 1H NMR (30 0MHz, CDCl3/TMS): =6. 82- 6.84 (d, 4H), 3. 90 -3. 94 (t, 2H), 3. 80(s, 3H), 3. 49 -3. 51 (t, 2H), 2. 01 -2. 11(m, 2H), 1.89-1.98(m, 2H), 1.51-1.61(m, 2H) -(p-methoxyphenoxy)hexyl bromides 1H NMR (30 0MHz, CDCl3/TMS): =6. 83- 6.85 (d, 4H), 3. 91 -3. 95 (t, 2H), 3. 81(s,... 13 38 40 29 30 32 DPn is the average degree of polymerisation 44 3. 4 FT-IR and 1H NMR characterisation Figure 2. 2 depicts the FT-IR spectra of pTHC4Br, pTHC6Br, pTHC10Br, pTHC6Br after I2 doping and 3- ( -bromohexyl)thiophene In the spectra of neutral polymers, for example in the spectrum of pTHC6Br, the presence of the bromide moiety afforded absorption bands at 125 4 (-CH2- deformation), 645 and 556... taken up in ether, and the ethereal extract was filtered from , -dimethoxyphenoxy alkane, washed with dilute sodium hydroxide and water, dried and distilled, giving recovered , -dibromodecane and - (p-tbutylphenoxy)decyl bromide 1 H NMR (30 0MHz, CDCl3/TMS): =7 .28 -7 .31 (m, 2H), 6. 82- 6.85 (m, 2H), 3. 92- 3. 96 (t, 2H), 3. 39 -3. 43 (t, 2H), 1.76-1.86(m, 2H), 1.66-1. 73( m, 2H), 1 .25 -1.46(m, 8H), 1 .30 (s, 9H) (4)... hr, concentrated and diluted with water The organic layer was taken up in ether, and the ethereal extract was filtered from , -dimethoxyphenoxy alkane, washed with dilute sodium hydroxide and water, dried and distilled, giving recovered , -dibromodecane and -(p-methylphenoxy)decyl bromide 1 H NMR (30 0MHz, CDCl3/TMS): =7 .25 -7 .26 (m, 2H), 6. 92- 6.94 (m, 2H), 3. 90- 3. 94 (t, 2H), 3. 38 -3. 42 (t, 2H), 2. 28... affect the polymers conductivity drastically The result is in contrast to earlier observations by Kaeriyama et al [22 ] In their study of polyalkylthiophenes where it was found that the introduction of longer n-alkyl chains decreases the resulting conductivity in the doped state Furthermore, with our polymers, different polymerisation conditions appear to have only a slight influence on electrical conductivity . 19,9 00 2. 0 7.9 73 27 pTHC8Br 93 25 ,20 0 1.8 10.4 87 13 pTHC10Br 73 22 ,000 2. 0 8.4 62 38 pTHC12Br 90 29 ,400 1.7 7.5 60 40 PHT 138 23 , 100 2. 7 . 9 .3 71 29 PBHT2 95 23 , 4 00 1.9 8 .2 70 30 PBHT3 92 22 ,6 00 2. 0 7.9 68 32 DPn is the average degree of polymeri s ation . 45 3. 4 FT - IR and 1 H NMR characterisation . Chapter 2 Syntheses and Characterisation of Electrically Conductive and Fluorescent Poly [3- ( - bromoalkyl)thiophenes] 32 1. Introduction 1.1 Conducting p olythiophene Amongst the