Research - Nachwuchsgruppe Dr. Merle Röhr

Publication

New theoretical methods for the exploration of functional landscapes. R{ö}hr, Merle I. S. In International Journal of Quantum Chemistry. Wiley, 2021.
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Endohedral Hydrogen Bonding Templates the Formation of a Highly Strained Covalent Organic Cage Compound. Schäfer, Natalie; Bühler, Michael; Heyer, Lisa; Röhr, Merle I. S.; Beuerle, Florian. In Chemistry {\textendash} A European Journal. Wiley, 2021.
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Perspectives in Dye Chemistry: A Rational Approach toward Functional Materials by Understanding the Aggregate State. Bialas, David; Kirchner, Eva; Röhr, Merle I. S.; Würthner, Frank. In Journal of the American Chemical Society. American Chemical Society ({ACS}), 2021.
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Tuning phenoxyl-substituted diketopyrrolopyrroles from quinoidal to biradical ground states through (hetero-)aromatic linkers. Rausch, Rodger; Röhr, Merle I. S.; Schmidt, David; Krummenacher, Ivo; Braunschweig, Holger; Würthner, Frank. In Chem. Sci., bl -. The Royal Society of Chemistry, 2021.
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Strongly fluorescent halochromic 2{,}6-di-tert-butyl-phenol-functionalised phenyl-{,} thienyl- and furyl-substituted diketopyrrolopyrrole (DPP) dyes were deprotonated and oxidised to give either phenylene-linked DPP1˙˙ biradical (y0 = 0.75) with a singlet open shell ground state and a thermally populated triplet state (ΔEST = 19 meV; 1.8 kJ mol−1; 0.43 kcal mol−1) or thienylene/furylene-linked DPP2q and DPP3q compounds with closed shell quinoidal ground states. Accordingly{,} we identified the aromaticity of the conjugated (hetero-)aromatic bridge to be key for modulating the electronic character of these biradicaloid compounds and achieved a spin crossover from closed shell quinones DPP2q and DPP3q to open shell biradical DPP1˙˙ as confirmed by optical and magnetic spectroscopic studies (UV/vis/NIR{,} NMR{,} EPR) as well as computational investigations (spin-flip TD-DFT calculations in combination with CASSCF(4{,}4) and harmonic oscillator model of aromaticity (HOMA) analysis). Spectroelectrochemical studies and comproportionation experiments further prove the reversible formation of mixed-valent radical anions for the DPP2q and DPP3q quinoidal compounds with absorption bands edging into the NIR spectral region.
Energetics and optimal molecular packing for singlet fission in {BN}-doped perylenes: electronic adiabatic state basis screening. Singh, Anurag; Humeniuk, Alexander; R{ö}hr, Merle I. S. In Physical Chemistry Chemical Physics. Royal Society of Chemistry ({RSC}), 2021.
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Impact of substituents on molecular properties and catalytic activities of trinuclear Ru macrocycles in water oxidation. Meza-Chincha, Ana-Lucia; Lindner, Joachim O.; Schindler, Dorothee; Schmidt, David; Krause, Ana-Maria; Röhr, Merle I. S.; Mitrić, Roland; Würthner, Frank. In Chem. Sci., 11(29), bll 7654–7664. The Royal Society of Chemistry, 2020.
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Herein we report a broad series of new trinuclear supramolecular Ru(bda) macrocycles bearing different substituents at the axial or equatorial ligands which enabled investigation of substituent effects on the catalytic activities in chemical and photocatalytic water oxidation. Our detailed investigations revealed that the activities of these functionalized macrocycles in water oxidation are significantly affected by the position at which the substituents were introduced. Interestingly{,} this effect could not be explained based on the redox properties of the catalysts since these are not markedly influenced by the functionalization of the ligands. Instead{,} detailed investigations by X-ray crystal structure analysis and theoretical simulations showed that conformational changes imparted by the substituents are responsible for the variation of catalytic activities of the Ru macrocycles. For the first time{,} macrocyclic structure of this class of water oxidation catalysts is unequivocally confirmed and experimental indication for a hydrogen-bonded water network present in the cavity of the macrocycles is provided by crystal structure analysis. We ascribe the high catalytic efficiency of our Ru(bda) macrocycles to cooperative proton abstractions facilitated by such a network of preorganized water molecules in their cavity{,} which is reminiscent of catalytic activities of enzymes at active sites.

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