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Lombeck F.,Albert Ludwigs University of Freiburg | Lombeck F.,Optoelectronics Group | Matsidik R.,Albert Ludwigs University of Freiburg | Komber H.,Leibniz Institute fur Polymerforschung Dresden e.V. | Sommer M.,Albert Ludwigs University of Freiburg
Macromolecular Rapid Communications | Year: 2015

Direct arylation (DA) of 2-chlorothiophene and 2-chloro-3-hexylthiophene with 4,7-dibromo-2,1,3-benzothiadiazole is used to synthesize 4,7-bis(5-chloro-2-thienyl)-2,1,3-benzothiadiazole (TBTCl2) and 4,7-bis(5-chloro-4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (DH-TBTCl2) in one step. Suitable conditions of the Suzuki polycondensations (SPC) of TBTCl2 and DH-TBTCl2 with the carbazole comonomer CbzPBE2 are established, furnishing PCDTBT and P(Cbz-alt-TBT) with high molecular weight and yield. Compared with control samples made from the corresponding dibromides, high-temperature NMR and UV-vis spectroscopy indicate similar properties for PCDTBT but an increased content of Cbz-Cbz homocouplings for P(Cbz-alt-TBT). (Chemical Equation Presented) © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.

Matsidik R.,Albert Ludwigs University of Freiburg | Martin J.,Albert Ludwigs University of Freiburg | Schmidt S.,Albert Ludwigs University of Freiburg | Obermayer J.,Albert Ludwigs University of Freiburg | And 6 more authors.
Journal of Organic Chemistry | Year: 2015

Pd-catalyzed direct arylation (DA) reaction conditions have been established for unsubstituted furan (Fu) and thiophene (Th) with three popular acceptor building blocks to be used in materials for organic electronics, namely 4,7-dibromo-2,1,3-benzothiadiazole (BTBr2), N,N-dialkylated 2,6-dibromonaphthalene-1,4,5,8-bis(dicarboximide) (NDIBr2), and 1,4-dibromotetrafluorobenzene (F4Br2). Reactions with BTBr2, F4Br2, and NDIBr2 require different solvents to obtain high yields. The use of dimethylacetamide (DMAc) is essential for the successful coupling of BTBr2 and F4Br2, but detrimental for NDIBr2, as the electron-deficient NDI core is prone to nucleophilic core substitution in DMAc as solvent but not in toluene. NDIFu2 is much more planar compared to NDITh2, resulting in an enhanced charge-transfer character, which makes it an interesting building block for conjugated systems designed for organic electronics. This study highlights direct arylation as a simple and inexpensive method to construct a series of important donor-acceptor-donor building blocks to be further used for the preparation of a variety of conjugated materials. © 2014 American Chemical Society.

Lombeck F.,Albert Ludwigs University of Freiburg | Lombeck F.,Optoelectronics Group | Komber H.,Leibniz Institute fur Polymerforschung Dresden e.V. | Gorelsky S.I.,University of Ottawa | Sommer M.,Albert Ludwigs University of Freiburg
ACS Macro Letters | Year: 2014

Homocouplings are identified as major side reactions in direct arylation polycondensation (DAP) of 4,7-bis(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (TBT) and 2,7-dibromo-9-(1-octylnonyl)-9H-carbazole (CbzBr2). Using size exclusion chromatography (SEC) and NMR spectroscopy, we demonstrate that both TBT and Cbz homocouplings occur at a considerable extent. TBT homocoupling preferentially occurs under phosphine-free conditions but can be suppressed in the presence of a phosphine ligand. Cbz homocoupling is temperature-dependent and more prevalent at higher temperatures. By contrast, evidence for chain branching as a result of unselective C-H arylation is not found for this monomer combination. These results emphasize that particular attention has to be paid to homocouplings in direct arylation polycondensations as a major source of main-chain defects, especially under phosphine-free conditions. © 2014 American Chemical Society.

Keivanidis P.E.,Imperial College London | Ho P.K.H.,National University of Singapore | Friend R.H.,Optoelectronics Group | Greenham N.C.,Optoelectronics Group
Advanced Functional Materials | Year: 2010

Organic photodiodes are presented that utilize solution-processed perylene diimide bulk heterojunctions as the device photoactive layer. The polymer (9,9â-dioctylfluorene-co-benzothiadiazole; F8BT) is used as the electron donor and the N,Nâ-bis(1-ethylpropyl)-3,4,9,10-perylene tetracarboxylic diimide (PDI) derivative is used as the electron acceptor. The thickness-dependent study of the main device parameters, namely of the external quantum efficiency (EQE), the short-circuit current (ISC), the open-circuit voltage (VOC), the fill factor (FF), and the dark current (ID) is presented. In as-spun F8BT:PDI devices the short-circuit EQE reaches the maximum of 17% and the VOC value is as high as 0.8 V. Device ID is in the nA mm-2 regime and it correlates with the topography of the F8BT:PDI layer. For a range of annealing temperatures ID is monitored as the morphology of the photoactive layer changes. The changes in the morphology of the photoactive layer are monitored via atomic force microscopy. The thermally induced coalescence of the PDI domains assists the dark conductivity of the device. ID values as low as 80 pA mm-2 are achieved with a corresponding EQE of 9%, when an electron-blocking layer (EB) is used in bilayer EB/F8BT:PDI devices. Electron injection from the hole-collecting electrode to the F8BT:PDI medium is hindered by the use of the EB layer. The temperature dependence of the ID value of the as-spun F8BT:PDI device is studied in the range of 296-216 K. In combination with the thickness and the composition dependence of ID, the determined activation energy Ea suggests a two-step mechanism of ID generation; a temperature-independent step of electric-field- assisted carrier injection from the device contacts to the active-layer medium and a thermally activated step of carrier transport across the device electrodes, via the PDI domains of the photoactive layer. Moreover, device ID is found to be sensitive to environmental factors. Minimizing the dark. The correlation between EQE and dark current in bulk heterojunction F8BT:PDI photodiodes is studied for a range of photoactive-layer thicknesses and reverse-bias voltages. For a given value of reverse bias operation, the improvement of the EQE reduces and the dark current increases as the photoactive layer becomes thinner. Dark current originates from the injection of electrons in the electron-accepting molecules (PDI) and from the subsequent carrier transport through the PDI network. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Komber H.,Leibniz Institute fur Polymerforschung Dresden e.V. | Mullers S.,Albert Ludwigs University of Freiburg | Lombeck F.,Albert Ludwigs University of Freiburg | Lombeck F.,Optoelectronics Group | And 3 more authors.
Polymer Chemistry | Year: 2014

A combined experimental and theoretical study on the synthesis and solution isomerization behavior of main chain copolymers with multiple spiropyran incorporation is presented. A series of alternating copolymers P(SP-alt-C x) of spiropyran (SP) and flexible linkers (Cx, x = 6,8,10) is synthesized by Suzuki polycondensation (SPC). Careful 1H NMR polymer end group analysis is carried out to reveal termination reactions that limit molecular weight. Although methylene indoline and salicyl aldehyde end groups are found arising from SP cleavage during polymerization, acceptable Mn,SEC up to 34 kg mol-1 is achieved. P(SP-alt-C x) can be transformed into the corresponding protonated form of the red alternating merocyanine (MC) polymer, P(MCH+-alt-Cx), in quantitative yield by direct acidification or pulsed ultrasound. The origin of the latter method lies in the sonochemical degradation of chloroform, which provides a continuous source of hydrochloric acid. Deprotonation of P(MCH +-alt-Cx) occurs upon the addition of a base resulting in the blue form P(MC-alt-Cx), as characterized by UV-vis spectroscopy and confirmed by density functional theory (DFT) calculations of model compounds. DFT further reveals P(MCH+-alt-Cx) to be the thermodynamically most stable form. It is proposed that the para-linkage to the phenyl-based comonomer Cx decreases acidity of protonated merocyanine and hence increases stability of P(MCH+-alt-Cx), which poses a marked difference compared to the commonly employed 6-nitro-substituted analogs. © 2014 The Royal Society of Chemistry.

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