- UV polymerization of oligothiophenes and their application in nanostructured heterojunction solar cells
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Thin films of 2,2′-bithiophene (2T) and 2,2′-5′,2″- terthiophene (3T) are polymerized by UV irradiation. The polymerization process can be observed by UV-vis and photoluminescence spectroscopy. If 2T is used as starting material, predominantly 4T (quarterthiophene) is formed, while 6T (sexithiophene) is formed if 3T is used as starting material. The same polymerization reaction occurs if solutions of 2T or 3T in chloroform or toluene are used or if a film of nanocrystalline titanium dioxide (nc-TiO2) is soaked with a 2T or a 3T solution. In the latter case the pores are (partly) filled with 4T or 6T, which acts as hole conductor. A photovoltaic response is observed when nc-TiO2/4T or nc-TiO2/6T interpenetrating structures are irradiated with visible light. The increase of oligomer length from 2T to 3T and the corresponding decrease in orientational freedom of the molecules strongly affects the ease of polymerization and the structural order of the compounds formed.
- Huisman, Carolien L.,Huijser, Annemarie,Donker, Harry,Schoonman, Joop,Goossens, Albert
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- Thallium(III) Trifluoroacetate-Trifluoroacetic Acid in the Chemistry of Polythiophenes. 1. Polymers from 2,2'-Bithiophene and 2,2',5',2''-Terthiophene. Mechanistic Aspects
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A new chemical method of simultaneous polymerization and doping of 2,2'-bithiophene (1) and 2,2',5',2''-terthiophene (2) using thallium(III) trifluoroacetate (TTFA) in trifluoroacetic acid (TFA) is reported.These reactions have been carried out at 20 deg C and at 72 deg C observing no remarkable differences in the quality of the polymers, which are undoped or compensated and purified to their neutral state by extraction with different solvents, and redoped in I2 atmosphere.Infrared spectra and conductivity measurements of the polymers, either as grown from the reaction mixture or after being redoped with I2, qualify them as good semiconductors, and their electron paramagnetic resonance (EPR) spectra show characteristic single lines with Lorentzian shapes and narrow line widths attributed to unpaired electrons delocalized along the carbon backbone chains. 2,2',5',2'',5'',2''',5''',2'''',5'''',2'''''-Sexithiophene (α-sexithiophene; 3) has been isolated and identified from one of the polymers during the purification process.EPR of the radical cation of 3 in CH2Cl2-TFA shows a symmetric multiplet which consists of a quintet (a4H = 2.18 G) of septets (a6H = 1.10 G).Variable-temperature EPR studies of 3 revealed the formation of its diamagnetic ?-dimer at low temperature in equilibrium with the radical cation.EPR and electronic spectra of reaction mixtures of 1 and 2 with TTFA/TFA show that 3 is the shortest oligomer whose radical cation is stable enough to be detected. 2 is protonated in TFA and it is suggested that 2 dimerizes to 3 in the presence of TTFA, through an oxidative coupling involving its conjugate acid.
- Gimenez, Elena,Carilla, Josep,Fajari, Lluis,Aleman, Carlos,Julia, Luis
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- Solution-phase microwave-assisted synthesis of unsubstituted and modified α-quinque- and sexithiophenes
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The facile synthesis of poorly soluble unsubstituted and modified α-quinque- and sexithiophenes under microwave irradiation in the liquid phase is described. The use of microwave irradiation allowed these compounds to be prepared in a few minutes and at high yields by means of the Suzuki cross-coupling reaction. Unsubstituted sexithiophene was obtained in 10 min via the one-pot borylation/Suzuki reaction, purified according to a very simple procedure, and isolated in 84% yield. The efficient synthesis of two new methylated quinque- and sexithiophenes displaying liquid crystalline properties is reported. A new microwave-assisted methodology for the conversion of aldehyde-terminated quinque- and sexithiophenes into the corresponding cyano derivatives is also described. The use of microwaves was extended to the Sonogashira coupling reaction and found to be very effective in the preparation of a quinquethiophene containing acetylenic spacers. The electronic and optical characterization of this compound is reported and discussed in relation to that of unsubstituted quinquethiophene.
- Melucci,Barbarella,Zambianchi,Di Pietro,Bongini
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p. 4821 - 4828
(2007/10/03)
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- A novel approach to a one-pot synthesis of unsubstituted oligo(α-thiophenes)
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Oligo(α-thiophenes) α-4T and α-8T were prepared by the following one-pot sequential conversions: thiophene (T) → α-2T → α-4T → α-8T. PdCl2-induced coupling of a mono-α-mercuration derivative of each of the n-mers T, α-2T, and α-4T was applied in these conversions.
- Buzhansky, Ludmila,Feit, Ben-Ami
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p. 7523 - 7525
(2007/10/03)
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- STUDY OF PHOTOGENERATED NONLINEAR EXCITATIONS IN A POLYTHIOPHENE MODEL COMPOUND: α-SEXITHIENYL
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Photogeneration of nonlinear excitations in the six thiophene unit oligomer of polythiophene has been studied.The formation of polarons is inferred from the observation of IRAV modes associated with midgap electronic transitions confirming the theoretical expectations that these electronic excitations are stable in short oligomers.
- Zamboni, R.,Ruani, G.,Taliani, C.,Pal, A. J.
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p. 113 - 116
(2007/10/02)
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- A CONVENIENT SYNTHESIS OF 2,5-THIENYLENE OLIGOMERS; SOME OF THEIR SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES
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Key words: 2,5-Thienylene oligomers, UV spectra, oxidation potentials, cyclic voltammetry.A convenient synthesis of a number of oligomeric thiophenes and oligomeric methyl-, and ethyl-substituted thiophenes as bulding blocks for novel conducting polymers is reported.The synthesis is based on a NiCl2(dppp) (dppp=Ph2PCH2CH2CH2PPh2) catalyzed coupling reaction between appropriately substituted bromothiophenes and Grignard compounds derived of them.The λmax of the UV spectra of the unsubstituted oligomeric thiophenes increases, as expected, with the number of thiophene units in the oligomers.Also, as expected, the oxidation potential Eox of these compounds decreases with increasing the number of thiophene units.In the series of the methyl- or ethyl-substituted oligomeric thiophenes such a clear cut relationship is not observed.This behavior is discussed on the basis of diminishing coplanarity due to steric hindrances by the alkyl groups in the 3,3'-positions, which results in a blue shift of the λmax of the UV spectra and decreased stability of the radical cation formed upon electrooxidation, manifesting itself by a higher oxidation potential.
- Pham, Chiem Van,Burkhardt, A.,Shabana, R.,Cunningham, David D.,Mark, Harry B.,Zimmer, Hans
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p. 153 - 168
(2007/10/02)
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- Thiophene Oligomers: Synthesis and Characterization
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The series of thiophene oligomers from bithienyl to α-sexithienyl has been synthesized according to the methods reported in the literature and some variation introduced by us.UV-visible, FT-IR, 13C-nmr and mass spectra of thiophene oligomers have been recorded and also cyclic voltammograms.Results are compared with data available in literature and are discussed in terms of conjugation length and coplanarity.Keywords: thiophene oligomers, 2,5-thienylene oligomers, 13C-nmr, FT-IR, spectroscopy
- Martinez, F.,Voelkel, R.,Naegele, D.,Naarmann, H.
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p. 227 - 232
(2007/10/02)
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- PREPARATION OF α-QUATER-, α-SEXI, AND α-OCTITHIOPHENES
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α-Quaterthiophene (1), α-sexithiophene (2), and α-octithiophene (3) (the highest member of α-oligothiophenes ever synthesized) were prepared from α-bithiophene, α-terthiophene, and α-quaterthiophene, respectively, via monobromination with N-bromosuccinimide followed by reductive coupling reaction with an activated nickel(0) reagent.
- Nakayama, Juzo,Konishi, Toru,Murabayashi, Shigeru,Hoshino, Masamatsu
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p. 1793 - 1796
(2007/10/02)
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- THE SYNTHESIS OF ALPHA-THIOPHENE OLIGOMERS VIA ORGANOBORANES
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Oligomers containing from 2 to 6 thiophene units attached by their 2 and 5 positions were synthesized unambiguously by iodine oxidation of a suitable ate complex obtained by stepwise reactions of 9-BBN with methanol, a 2-lithiothiophene, boron trifluoride etherate, and a second 2-lithiothiophene.This is a one-pot procedure, carried out under nitrogen between -80 deg C and 0 deg C.
- Kagan, Jacques,Arora, Sudershan K.
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p. 4043 - 4046
(2007/10/02)
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- THE SYNTHESIS OF ALPHA-THIOPHENE OLIGOMERS BY OXIDATIVE COUPLING OF 2-LITHIOTHIOPHENES
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Alpha-thiophene oligomers containing an even number of thiophene rings can be obtained with very good yields by reacting a suitable thiophene precursor with 0.5 equivalent of lithium diisopropylamide in dry THF, followed by the oxidation of the α-lithio derivative with cupric chloride.The Scheme is illustrated with the synthesis of 2,2'-bithienyl, α-quaterthienyl, and α-sexithienyl in 83, 85, and 73 percent yields from thiophene, 2,2'-bithienyl, and α-tertthienyl respectively.
- Kagan, Jacques,Arora, Sudershan K.
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p. 1937 - 1940
(2007/10/02)
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