Selected recent publications:
Pecyna, J.; Rončević, I.; Michl, J. “Insertion of Carbenes into Deprotonated nido-Undecaborane, B11H13(2-)”, Molecules 2019, 24, 3779.
Abstract: We have examined the insertion of carbenes carrying leaving groups into the [nido-B11H13]2- dianion to form the [closo-1-CB11H12]- anion. The best procedure uses CF3SiMe3 and LiCl as the source of CF2. It is simple, convenient, and scalable, and proceeds in 70-90% yield. Density functional calculations have been used to develop a mechanistic proposal that accounts for the different behavior of CF2, requiring only one equivalent of base for successful conversion of Na[nido-B11H14]- to [closo-1-CB11H12]-, and CCl2 and CBr2, which require more.
Wen, J.; Turowski, M.; Dron, P. I.; Chalupský, J.; Grotjahn, R.; Maier, T. M.; Fatur, S. M.; Havlas, Z.; Johnson, J. C.; Kaupp, M.; Michl, J. “Electronic States of 2,3-Diamino-1,4-naphthoquinone and its N-Alkylated Derivatives”, J. Phys. Chem. C 2020, 124, 60.
Abstract: Diaminoquinones with captodatively stabilized biradicaloid structure are candidates for singlet fission, but few such compounds are known. We report the solution spectroscopy and photophysics of 1,2,2,3-tetramethyl-2,3-dihydro-1H-naphtho[2,3-d]imidazole-4,9-dione (1): its steady-state and transient UV-visible absorption, linear dichroism in stretched poly(vinyl alcohol), and magnetic circular dichroism. We also describe the absorption spectra of the stable radical ions 1∙+ and 1∙− and of two parent structures, 2,3-diamino-1,4-naphthoquinone (2) and 2,3-bis(methylamino)-1,4-naphthoquinone (3). The spectra are interpreted and electronic transitions are assigned by comparison with results of DFT and MS-CASPT2 calculations.
Plutnar, J.; Givelet, C.; Lemouchi, C.; Dytrtová-Jaklová, J.; Teat, S. J.; Michl, J. “Mechanical vs. Electronic Strain: Oval-Shaped Alkynyl-Pt(II)-Phosphine Macrocycles”, Organometallics 2019, 38, 4633.
Abstract: Pyridine-terminated molecular rods and either (i) the cis-(dppp)(I)Pt(C≡C-triptycene-C≡C)Pt(I)(dppp) rod or (ii) the trans-(PEt3)2(I)Pt(C≡C-biphenyl-C≡C)Pt(I)(PEt3)2 rod assemble into macrocycles, characterized by NMR, IMS-ESI, and in two cases also single crystal X-ray diffraction. The former form rectangles with bidentate phosphine-containing cis-coordinated Pt(II)-alkyne corners. In the latter, the preference of the Pt centers for trans configuration overrules the preference of the triple bonds for linearity and NMR shows that they have oval structures with alternating bent rod and bent trans (C≡C)(Py)Pt(PEt3)2 components, in agreement with density functional theory calculations.
Miller, J. R.; Cook, A. R.; Šimková, L.; Pospíšil, L.; Ludvík, J.; Michl, J. “The Impact of Huge Structural Changes on Electron Transfer and Measurement of Redox Potentials: Reduction of ortho-12-Carborane”, J. Phys. Chem. B 2019, 123, 9668.
Abstract: A massive structural change accompanies electron capture by the 1,2-dicarba-closo-dodecaborane cage molecule (1). Bimolecular electron transfer (ET) by pulse radiolysis found a reduction potential of E0= -1.92 V vs. Fc+/0 for 1 and rate constants that slowed greatly for ET to or from 1 when the redox partner had a potential near this E0. Similarly, two electrochemical techniques could detect no current at potentials near E0, finding instead peaks or polarographic waves near -3.1 V, which is 1.2 V more negative than E0. Voltammetry could determine rate constants, but only near -3.1 V. DigiSim simulations require electrochemical rate constants near 1x10-10 cm/s at E0, a factor of 10-10 relative to molecules undergoing facile ET. This factor of 10-10 compared to ~10-5 for bimolecular ET presents a puzzle. We propose that a manifestation of one of the “Frumkin Effects” in which only part of the applied voltage is available to drive ET at the electrode provides a resolution to this puzzle.
Michl, J. “Singlet Fission: Toward More Efficient Solar Cells”, Substantia 2019, 3, 45.
Abstract: A survey is provided of the current status of singlet fission as a tool for bypassing the Shockley-Queisser limit on the efficiency of single-junction solar cells.