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Publisher: London : RSC Publishing × Subject: Chemical reactions ×

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    Thermally triggered optical tuning of π-conjugated graft copolymers based on reversible Diels–Alder reaction
    (London : RSC Publishing, 2016) Ahner, J.; Micheel, M.; Kötteritzsch, J.; Dietzek, B.; Hager, M.D.
    In order to design a π-conjugated polymer film with tunable optical properties by thermally triggered activation of energy transfer after processing, two monodisperse phenylene ethynylene based oligomers with different optical properties were synthesized and attached to aliphatic polymers as π-conjugated side chains. Subsequently, the exchange of the side chain chromophores between the prepared donor and acceptor graft polymers in the solid state based on a reversible Diels–Alder reaction was studied in detail. The resulting donor–acceptor graft copolymer exhibits intra polymer energy transfer upon excitation of the donor moiety. The photophysical properties of the original and exchanged graft copolymers were investigated by means of absorption and emission spectroscopy. This novel concept opens the possibility for optical tuning of π-conjugated polymer films after processing as well as applications as thermally triggered sensor systems.
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    Gas hydrates model for the mechanistic investigation of the Wittig reaction “on water”
    (London : RSC Publishing, 2016) Ayub, Khurshid; Ludwig, Ralf
    Theoretical mechanistic details for “on water” Wittig reaction of a stabilized ylide with benzaldehyde are presented and compared with a similar reaction under neat conditions. A gas hydrate structure consisting of 20 water molecules has been applied as a water surface for the reaction. The model is chosen to capture non-bonding interactions over a larger area in order to better account for the “on water” effect. The calculated acceleration for the cis-selective Wittig reaction is more than that for the trans-selective Wittig reaction. The “on water” acceleration for the Wittig reaction is due to greater number of non-bonding interactions in the transition state, compared to the starting material. The greater acceleration for the cis-selective Wittig over the trans-selective Wittig has been rationalized on the basis of non-bonding interactions in addition to hydrogen bonding. Besides accelerating the reaction, water also affects the pathway for the reaction. Decomposition of cisOP2 to alkene is estimated as a barrierless process. Moreover OP2 is more stable than OP1 for both cis and trans-selective Wittig reactions, opposite to what is observed for the neat reaction.
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    Mixed-halide triphenyl methyl radicals for site-selective functionalization and polymerization
    (London : RSC Publishing, 2021) Chen, Lisa; Arnold, Mona; Blinder, Rémi; Jelezko, Fedor; Kuehne, Alexander J. C.
    Derivatives of the stable, luminescent tris-2,4,6-trichlorophenylmethyl (TTM) radical exhibit unique doublet spin properties that are of interest for applications in optoelectronics, spintronics, and energy storage. However, poor reactivity of the chloride-moieties limits the yield of functionalization and thus the accessible variety of high performance luminescent radicals. Here, we present a pathway to obtain mixed-bromide and chloride derivatives of TTM by simple Friedel–Crafts alkylation. The resulting radical compounds show higher stability and site-specific reactivity in cross-coupling reactions, due to the better leaving group character of the para-bromide. The mixed halide radicals give access to complex, and so far inaccessible luminescent open-shell small molecules, as well as polymers carrying the radical centers in their backbone. The new mixed-halide triphenyl methyl radicals represent a powerful building block for customized design and synthesis of stable luminescent radicals.