Abstract
Poly[3-(6-bromohexyl)thiophene] (1) and poly[3-(12-bromododecyl)thiophene] (2) were synthesized by chemical polymerization of their respective monomers, 3 and 4, using FeCl3. NMR spectroscopy showed 81% of head-to-tail couplings and GPC showed M n = 51,500 and 91,100 with PDIs of 5.2 and 1.7 for 1 and 2, respectively. Conductivities of the I2- and FeCl3doped 1 were 18 and 7.5 S cm -1 and for 2 were 32 and 46 S cm -1 , respectively. Poly[3-(6iodohexyl)thiophene] (8) was prepared by SN2 displacement (>97%), using NaI, on 1. Poly[6-(3thienyl)-1-hexyl S-thioacetate] (10a) and poly[12-(3-thienyl)-1-dodecyl S-thioacetate] (10b) were prepared from 1 by post-polymerization SN2 reactions. They were insoluble in organic solvents and had 13 C CP-MAS NMR spectra consistent with the structures. Reaction of 1 with thiourea followed by basic hydrolysis gave poly[3-(6-mercaptohexyl)thiophene] (11). This thiol functionalized polymer was also insoluble in common organic solvents and it, too, had a 13 C CPMAS NMR spectrum consistent with the structure. Polymers 10a and 11 showed pressed pellet conductivities of 4 x 10 -5 and 2.3 x 10 -2 S cm -1 when doped with FeCl3, respectively and 8 x 10 -5 and 0.44 S cm -1 when doped with I2, respectively. TGA of polymers 1, 8 and 11 showed thermal decomposition in two stages.
Highlights
Because of their electrical conductivity and electroluminescent properties, polythiophenes have been under intense investigation for many years
Iodohexyl)thiophene] (8) was prepared by SN2 displacement (>97%), using NaI, on 1
Bromine and iodine containing polymers The monomers, (6-bromohexyl)thiophene (3) and 3-(12-bromododecyl)thiophene (4), were prepared as shown in Scheme 1 using a modification of the synthesis reported by Bäuerle.[9]
Summary
Because of their electrical conductivity and electroluminescent properties, polythiophenes have been under intense investigation for many years. This is to be compared with the significantly lower number average molecular weights of 12,300-23,400 obtained by Ng, et al for 1 using FeCl3 polymerization.[7] Films of 1 and 2 were deep red/burgundy in color with very similar UV-vis absorption maxima at 492 nm and 505 nm, respectively, and THF solutions of these two polymers showed similar absorption spectra with λmax of 436 and 438 nm, respectively, all close to the values reported for poly(3-hexylthiophene)[17,18,19] and poly(3-dodecylthiophene)[19] prepared using FeCl3.
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