Synthesis and properties of α,ω-phenyl-capped bithiophene derivatives

Abstract

Nine different a,v-phenyl-endcapped bithiophenes were synthesised, and the effect of the different side chains on the liquid crystalline properties, alignment ability and charge carrier mobility have been studied. An increase in chain length leads to a decrease in the liquid crystalline-isotropic phase (clearing) transition temperature. Remarkably, introduction of an asymmetric carbon centre close to the p-conjugated segment resulted in the loss of the liquid crystalline phase. Alignment on rubbed polyimide was obtained for the liquid crystalline thiophene derivatives lacking heteroatoms in the side chain and for the chiral a,v-phenyl-endcapped bithiophene. Some bithiophenes showed bipolar charge transport in time-of-flight (TOF) measurements, with mobilities up to 3 6 10 23 cm 2 V 21 s 21 in the liquid crystalline state. Field effect transistors revealed mobility for holes up to 1 6 10 23 cm 2 V 21 s 21 (crystalline state). From the data set obtained, it can be concluded that the use of linear hydrocarbon chains as solubilising tails in these types of p-conjugated building blocks gives the best overall electronic performance. Results and discussion SynthesisThe different phenyl-endcapped bithiophene derivatives (Chart 1, 2-10) were synthesised according to Scheme 1. The

5,5′-Bis-(alkylpyridinyl)-2,2′-bithiophenes: synthesis, liquid crystalline behaviour and charge transport

“…This journal is © The Royal Society of Chemistry 2014 leads to materials with either identical or different alkyl chains (Scheme 3). The key reaction for the construction of the aromatic core of LC's of type 3 is the Negishi coupling of an arylzinc chloride with 2-bromo-5-iodopyridine (9). The reaction proceeds with good selectivity at the C-I site, producing 2-bromo-5-arylpyridines such as 13.…”

“…15 The aryl bromide 13 underwent Kumada coupling with n-tridecylmagnesium bromide in the presence of Ni(II)-catalyst to produce 14 in 63% yield. The aryl bromide 15, obtained by a standard bromination with NBS in DMF in 72% yield, underwent the sequence of lithiationtransmetallation to Zncoupling with 2-bromo-5-iodopyridine (9) to give new aryl bromide 16 in overall 52% puried yield. Alkylation of 16 with two different alkyl Grignard reagents (R ¼ n-C 7 H 15 and n-C 13 H 27 ) produced asymmetric 2h (43%) and symmetric 2g (26%), the latter which had also been prepared by Stille coupling (Scheme 2).…”

“…8 In addition, 5,5 0bis-(4-n-alkylphenyl)-2,2 0 -bithiophenes 1b,c with longer tails were also prepared, and the charge transport was examined by TOF and in OFET. 9 Mesogen 1b with n-octyl chains showed ambipolar charge transport with m h ¼ 4 Â 10 À3 cm 2 V À1 s À1 and m e ¼ 3 Â 10 À3 cm 2 V À1 s À1 determined by TOF, while OFET mobilities of 1b and 1c at 20 C were found to be 1 Â 10 À3 cm 2 V À1 s À1 and 1 Â 10 À4 cm 2 V À1 s À1 respectively. 9 Much higher OFET mobilities m h (0.14 cm 2 V À1 s À1 (I on /I off ratio 9 Â 10 4 ) and 0.18 cm 2 V À1 s À1 (I on /I off ratio 9 Â 10 6 )) were reported for 5,5 0bis-(4-n-alkylphenyl)-2,2 0 -bithiophenes 1d (butyl chains) and 1b (octyl chains), respectively, at higher substrate temperatures of 40 and 50 C. 10 Material 1b puried by vacuum sublimation and vacuum deposited 10 showed much faster charge transport in an OFET device in comparison with the same compound puried by chromatography and solution-processed from toluene 9 (0.18 cm 2 V À1 s À1 and 1 Â 10 À3 cm 2 V À1 s À1 , respectively).…”

“…An attempt to apply the general synthetic strategy outlined in Scheme 1 to the synthesis of isomeric liquid crystals of type 3 with the nitrogen atoms distant from the thiophene rings was less successful (Scheme 2). The Negishi coupling of 2-bromo-5iodopyridine (9) with the double zinc chloride derivative of 2,2 0bithiophene (2) resulted in the formation of the dibromide 10, but its subsequent alkylation reaction proved to be problematic due to poor solubility. The best result was obtained when an excess of Grignard reagent was added to a suspension of the starting dibromide and NiCl 2 (dppe) in boiling THF, but even in the best case the yield of the desired material 3b was only 20%.…”

Luminescent Organic Semiconducting Langmuir Monolayers

“…The synthesis of compound D2-Und-PTTP-TMS is shown in Scheme 1. The first step was the preparation of 5-(4-undec-10-en-1-yl-phenyl)-2,2′-bithiophene (Und-PTT) by Suzuki cross-coupling between 1-bromo-4-undec-10-enyl-benzene 35 and 2-(2,2′-bithien-5-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane. 36 After purification by column chromatography on silica gel, Und-PTT was obtained as a colorless solid in 85% isolated yield.…”