Suchergebnisse

In this work, the synthesis of N,N'-dialkyl-6,6'-dibromoisoindigo derivatives by continuous-flow chemistry is explored as a means to enhance material availability and structural diversity, in particular toward the application of isoindigo-based semiconductors in high-performance organic photovoltaic devices. The individual steps in the conventional batch synthesis protocol are evaluated and, when needed, adapted to flow reactors. To overcome the low solubility of non-alkylated 6,6'-dibromoisoindigo in common organic solvents, the flow condensation reaction between the 6-bromo-isatin and 6-bromo-oxindole precursors is evaluated in polar aprotic solvents. Dialkylation of 6,6'-dibromoisoindigo is readily performed in flow using a solid-phase reactor packed with potassium carbonate. In an alternative strategy, solubility is ensured by first introducing the N-alkyl side chains on 6-bromo-isatin and 6-bromo-oxindole (accessible via a high-yielding flow reduction of alkylated 6-bromo-isatin), followed by condensation using the conventional method in acetic-hydrochloric acid medium. The N, N'-dialkylated 6,6'-dibromoisoindigo derivatives indeed show enhanced solubility in the hot reaction mixture compared to the non-alkylated material but eventually precipitate when the reaction mixture is cooled down. Nevertheless, the condensation between both alkylated starting materials is achieved in flow without any blockages by keeping the outlet from the reactor heated and as short as possible. The latter strategy allows the preparation of both symmetrically and asymmetrically N-substituted isoindigo compounds. ; This work was supported by the project ORGANEXT (EMR INT4-1.2-2009-04/054), selected in the frame of the operational program INTERREG IV-A Euregio Maas-Rijn, and the IAP 7/05 project FS2 (Functional Supramolecular Systems), granted by the Science Policy Office of the Belgian Federal Government (BELSPO). We are also grateful for financial support by the Research Program of the Research Foundation - Flanders (FWO) (project G.0415.14 N and M. ERA-NET project RADESOL). G. Pirotte thanks Hasselt University for his PhD scholarship. J. Brebels and P. Verstappen acknowledge the Agency for Innovation by Science and Technology in Flanders (IWT) for their PhD grants. We further acknowledge Hercules for providing the funding for the LTQ Orbitrap Velos Pro mass spectrometer. Hasselt University and IMO-IMOMEC are partners within the Solliance network, the strategic alliance for research and development in the field of thin-film PV energy in the Eindhoven-Leuven-Aachen region.

Although controlled polymerization procedures for conjugated polymers have considerable advantages with respect to molar mass and end group control, the material scope has been very limited, in particular considering block copolymers and donor–acceptor type all-conjugated polymers, imposing considerable challenges upon the synthetic polymer community. In this work, a push–pull monomer consisting of a thiophene (donor) and a pyridine (acceptor) unit is synthesized and subsequently polymerized via Kumada catalyst-transfer polymerization using a nickel catalyst (GRIM polymerization). In this way, an alternating donor–acceptor copolymer is obtained via a chain-growth mechanism. Furthermore, an all-conjugated block copolymer containing a poly(3-hexylthiophene) block and the alternating copolymer is successfully prepared in a one-pot procedure as well. The diblock structure is confirmed by comparison of the thermal, electrochemical, and spectroscopic properties of the block copolymer and its constituting polymer parts. ; This work was supported by the IAP 7/05 project "Functional Supramolecular Systems", granted by the Science Policy Office of the Belgian Federal Government (BELSPO). We are also grateful for financial support by the Research Program of the Research Foundation−Flanders (FWO) (project G.0415.14N). S.G. acknowledges Hasselt University for her (BOF) doctoral grant. TA Instruments is acknowledged for the RHC equipment.

Three extended molecular chromophores, differing in their central acceptor moiety and specifically designed as electron donor components for small molecule organic solar cells, are synthesized via a two-fold-C-H arylation protocol. Upon removal of the side products inherent to the applied direct (hetero) arylation procedure, a record power conversion efficiency of 5.1% is achieved. ; We acknowledge financial support from the Science Policy Office of the Belgian Federal Government (BELSPO; IAP 7/05 project FS2), the Agency for Innovation by Science and Technology in Flanders (IWT; PhD grants J. Brebels and T. Vangerven) and the Research Programme of the Research Foundation - Flanders (FWO; M.ERA-NET project RADESOL and projects G.0415.14N/G.0B67.15N).

Conjugated polymers and small molecules based on alternating electron-donating (D) and electronaccepting (A) building blocks have led to state-of-the-art organic solar cell materials governing efficiencies beyond 10%. Unfortunately, the connection of D and A building blocks via cross-coupling reactions does not always proceed as planned, which can result in the generation of side products containing D-D or A-A homocoupling motifs. Previous studies have reported a reduced performance in polymer and small molecule solar cells when such defect structures are present. A general consensus on the impact of homocouplings on device performance is, however, still lacking as is a profound understanding of the underlying causes of the device deterioration. For differentiating the combined effect of molecular weight and homocouplings in polymer solar cells, a systematic study on a small molecule system (DTS(FBBTh2)2) is presented. The impact of homocouplings on nanomorphology, thermal, and electro-optical properties is investigated. It is demonstrated that small quantities of homocouplings (<10%) already lead to suboptimal device performance, as this strongly impacts the molecular packing and electronic properties of the photoactive layer. These results highlight the importance of material purity and pinpoint homocoupling defects as one of the most probable reasons for batch-to-batch variations. ; The authors thank Hasselt University and the Research Foundation Flanders (FWO) for financial support. The collaboration between Hasselt and Mons is supported by the Science Policy Office of the Belgian Federal Government (BELSPO; IAP 7/05 project FS2). T.V. and M.D. acknowledge the Agency for Innovation by Science and Technology in Flanders (IWT) for their Ph.D. grants. K.V. and J.B. thank the German Federal Ministry for Education and Research (BMBF) for funding through the InnoProfille project "Organische p-i-n Bauelemente 2.2". The M-ERA.NET project "RADESOL" is funded under the EU Seventh Framework Programme (FP7/2007-2013) Grant 234648/O70. J.W.A. acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 681881). The authors further acknowledge Huguette Penxten for the CV measurements. The research in Mons is also supported by FNRS-FRFC and the European Commission/Walloon Region (FEDER−BIORGEL project). D.B. is an FNRS Research Director. The authors finally acknowledge TA Instruments for the RHC equipment.