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The influence of the regioregularity on the second-order nonlinear optical response of polythiophenes in solution was investigated. A series of chiral poly((S)-3,7- dimethyloctylthiophene)s with va...

The performance of catalyst transfer polymerization (CTP) reactions which depend on catalyst association was studied on 3,6-dioctylthiothieno[3,2-b]thiophene (TT) monomers. This monomer was selected because a strong association of the catalyst is expected, since the aromaticity of thienothiophene is largely maintained when the catalyst and thienothiophene associate. This study includes both reported and unreported Ni- and Pd-catalyst systems. It is found that no polymer formation can be observed using Ni-catalysts, whereas Pd-catalysts show a similar behavior as for other monomer systems. During the study of the Ni-catalyzed CTPs, the π-associated Ni0-complex has been isolated in situ and displayed a high stability in solution. It is shown that the associated complex interferes with the polymerization reaction and even prevents polymer formation. Furthermore, this complex prevented any Kumada-coupling reaction in the presence of the TT unit, as it serves as a “trapping site” for free Ni0 catalyst entities. Ni0-trapping 2 does not occur during polymerization of 3-alkylthiophene, confirming the presence of the π-associated Ni0-complex in this polymerization. This introduces a new convenient method of probing Ni0-association during all Ni-catalyzed reactions. Furthermore, these results establish the presence of an upper limit to the catalyst association strength -above which oxidative addition is prevented and the polymerization is inhibited- and they therefore add extra considerations for optimal catalyst design. ispartof: Macromolecules vol:47 issue:24 pages:8548-8555 status: published

The formation in solution of a supramolecular graft copolymer bearing conjugated blocks is demonstrated using diffusion ordered NMR spectroscopy (DOSY). A tailor-made poly(3-(2-ethylhexyl)thiophene) (P3EHT) with a phenol end group is synthesized. For this purpose, the chain-growth mechanism of the polymerization of 2-bromo-5-chloromagnesio-3-alkylthiophenes in the presence of a Ni(dppp) catalyst (dppp = 1,3-bis(triphenylphosphino)propane) is exploited, as it enables the use of functionalized initiators to introduce specific end groups. The so-obtained polythiophene was subsequently mixed in solution with poly(4-vinylpyridine) (P4VP) to enable phenol-pyridine hydrogen bonding. The formation of the supramolecular graft copolymer is studied using DOSY-measurements. Based on the results thereof, the amount of P3EHT attached to the P4VP is calculated and the association constant of the hydrogen bond is estimated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 804–809

Organic microcrystals obtained from an octupolar molecule are studied by polarized nonlinear optical microscopy. While two-photon fluorescence microscopy is employed to verify the monocrystallinity of the analyzed domains, second-harmonic generation microscopy allowed determination of the point group symmetry of the crystallites. This combined analysis revealed that the achiral, octupolar molecules form chiral and polar conglomerate structures; the former are confirmed by circular dichroism spectroscopy. We additionally present a convenient and straightforward image analysis protocol, based on polarization dependent second-harmonic generation microscopy. This allows assessing the local organization and homogeneity of crystalline structures, which is highly relevant for technological applications, with high resolution and sensitivity.

This paper presents the synthesis and characterization of low-bandgap materials based on cyclopenta[1,2-b;3,4-b′]dithiophene (CPDT). An array of electron-poor monomers is synthesized and used to prepare homo- and alternating donor–acceptor copolymers. This yields polymers with low bandgaps (Eg = 1.12–1.23 eV) and broad light absorption (400–1100 nm). The influence of the electron-withdrawing substituent and the donor material on the polymer properties is studied. It is demonstrated that the low bandgap is not a result of intramolecular charge transfer, but of a transition localized in the electron-poor CPDT monomer. The bandgap can be correlated with the substituent on the CPDT monomer and is relatively independent of other parameters, resulting in materials with an easily tunable bandgap.

A poly(3-octylthiophene)-block-poly(3-butylthiophene) block copolymer was synthesized in a one-pot block copolymerization reaction, starting from a functional o-tolyl initiator in order to maximize A–B diblock copolymer formation. First, the composition of this block copolymer is extensively studied using gel permeation chromatography (GPC) and 1H NMR measurements. A complete block copolymer formation is obtained with almost equal block length; B–A–B block copolymer contamination is shown to be very limited. In a second part, the self-assembly was analysed through differential scanning calorimetry (DSC), atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) measurements, focusing on the microphase separation. A direct visualization of the different microphases can be obtained with STM. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: Wouter Dujardin (ResearcherID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 29 September 2014; Accepted 22 December 2014; Accepted Manuscript published 22 December 2014; Version of Record published 8 January 2015 ispartof: RSC Advances vol:5 issue:12 pages:8721-8726 status: published

Recently, much research has been performed on developing low-bandgap polymers for e.g. harvesting solar energy. In the quest to improve these properties, little attention has been paid to their nonlinear optical properties, despite their interesting linear optical spectra and structural similarities to certain nonlinear optically active compounds. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b′] dithiophen-4-ylidenedioctylmalonate). The unexpectedly large nonlinear optical susceptibilities and the thermal and temporal stability of the material compare favorably to other novel nonlinear optical materials despite the lack of a donor-acceptor dye. Additionally, the polymer displays a very low absorption in the relevant wavelength region. These results demonstrate the promise of these materials for nonlinear optical devices. publisher: Elsevier articletitle: Optical second harmonic generation in a low-bandgap polymer journaltitle: Materials Chemistry and Physics articlelink: http://dx.doi.org/10.1016/j.matchemphys.2014.06.003 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved. ispartof: Materials Chemistry and Physics vol:147 issue:3 pages:356-359 status: published

Recent research has focused on developing low-bandgap polymers for harvesting solar energy, fine-tuning desirable properties including power conversion efficiency, carrier mobilities and broad light absorption. However, little attention has been paid to their nonlinear optical properties. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b']dithiophen-4-ylidenedioctylmalonate). Despite being amorphous and lacking a typical donor-acceptor dye, these films display large nonlinear optical susceptibilities. Coupled with their stability and low absorption in the relevant wavelength region, these polymer films compare favorably to other materials. Our results show the promise of low-bandgap polymers for nonlinear optical applications.

In this manuscript, the Kumada catalyst transfer polymerization (KCTP) of cyclopenta[2,1-b;3,4-b′]dithiophene (CPDT), a monomer consisting of two fused thiophene entities, is investigated. It is shown that this polymerization follows a controlled chain-growth mechanism. Furthermore, the formation of block copolymers with poly(3-alkylthiophene)s is investigated, and it is shown that these block copolymers can be formed if 3-alkylthiophene is used as the first block and CPDT as the second. The resulting all-conjugated block copolymers consist of two blocks with substantially different electronic and physical properties and it is shown that the blocks influence each other, resulting in a unique material with different properties compared to a blend. © 2013 American Chemical Society. ispartof: Macromolecules vol:46 issue:22 pages:8888-8895 status: published

Faraday rotation, the rotation of the polarization of light due to a magnetic field in the direction of propagation of the light, is used in applications ranging from quantum memory to the detection of biomagnetic fields. For these applications large Faraday rotation is necessary, but absorption of light is detrimental. In search of these properties, we have characterized the Verdet constant of a so far unexplored class of mesogenic organic molecules. We report their spectra and provide an interpretation. A Verdet constant of almost 2.5 × 105 deg T–1 m–1 is found around 520 nm. This Verdet constant is 3 orders of magnitude larger than the largest known for organic molecules in a region without spectral features. We attribute this enormous Faraday rotation to resonant enhancement by a triplet excitation that does not appear in the linear absorption spectrum and to near-resonant enhancement by low-energy singlet excitations. Furthermore we are able to switch the Faraday rotation by changing the liquid crystal phase of the compound. These results demonstrate a new class of Faraday rotating materials with great potential to replace current materials and improve existing applications. The inherent flexibility in the synthesis of this class of molecules opens a new field of research in Faraday rotation. ispartof: Chemistry of Materials vol:25 issue:7 pages:1139-1143 status: published

Polythiophenes with alcohol, tosylate, azide, ethynylene, carboxylic acid, and amine end groups were prepared by a combination of functionalized nickel initiators and postpolymerization reactions. The azide and ethynylene polymers were subsequently used in a click reaction to produce a conjugated block copolymer. Finally, a conjugated triblock-copolymer was synthesized by means of a chain growth polymerization initiated by a binuclear nickel initiator. ispartof: Macromolecules vol:44 issue:15 pages:6017-6025 status: published

This work reports a synthetic strategy to generate poly(3-alkylthiophene)s (P3ATs) with joint-simultaneous control of the molar mass and the regioregularity. A series of chiral P3ATs with different regioregularities is synthesized using a Pd(RuPhos)-catalyzed chain-growth polymerisation. All polymers have molar masses and polydispersities (PDI) that lie within a narrow region. Furthermore, it is shown that the Pd-catalyst forms all kinds of couplings [head-to-tail (HT), tail-to-tail (TT) and head-to-head (HH)] to a similar extent, which allows insertion of predictable amounts of regio-irregularities into the polymer chain. This enables a thorough study of the influence of the regioregularity on the properties of P3AT, which was performed using UV-vis and circular dichroism (CD) spectroscopy, differential scanning calorimetry (DSC) and atomic force microscopy (AFM) measurements. Unexpectedly, it is found that under “kinetic” conditions the highest crystallinity, π-stacking, supramolecular organisation and chiral expression are not obtained for fully regioregular P3AT with 100% HT couplings, but that a small amount of regio-irregularity increases these properties and the chiral expression. Under “thermodynamic” conditions (after annealing, very slow solvent evaporation or very slow cooling from the melt), this effect is less pronounced or not found. This behaviour can be explained by a higher degree of motional freedom within the non-perfect polymer chains due to the increased steric repulsion from the HH-couplings, which leads to a more easy stacking under “kinetic” conditions.