Leos Valenta

All Publications

• Fluorination Affects the Force Sensitivity and Nonequilibrium Dynamics of the Mechanochemical Unzipping of Ladderanes. Journal of the American Chemical Society Horst, M., Holm, S., Valenta, L., Kouznetsova, T. B., Yang, J., Burns, N. Z., Craig, S. L., Martínez, T. J., Xia, Y. 2024

  Abstract

  When multiple reaction steps occur before thermal equilibration, kinetic energy from one reaction step can influence overall product distributions in ways that are not well predicted by transition state theory. An understanding of how the structural features of mechanophores, such as substitutions, affect reactivity, product distribution, and the extent of dynamic effects in the mechanochemical manifolds is necessary for designing chemical reactions and responsive materials. We synthesized two tetrafluorinated [4]-ladderanes with fluorination on different rungs and found that the fluorination pattern influenced the force sensitivity and stereochemical distribution of products in the mechanochemistry of these fluorinated ladderanes. The threshold forces for mechanochemical unzipping of ladderane were decreased by α-fluorination and increased by γ-fluorination; these changes correlated to the different stabilizing or destabilizing effects of fluorination patterns on the first transition state. Using ab initio steered molecular dynamics (AISMD), we compared the product distributions of synthesized and hypothetical ladderanes with different substitution patterns. These calculations suggest that fluorination on the first two bonds of ladderane gives rise to a larger fraction of dynamic trajectories and a larger fraction of E-alkene product through a mechanism resulting from larger momentum because of the greater atomic mass of fluorine. Fluorination on the third and fourth rungs instead gives a larger fraction of E-alkene product primarily due to electronic effects. These combined experimental and computational studies of the mechanochemical unzipping of fluorinated ladderanes provide an example of how relatively simple substituents can affect the extent of nonstatistical dynamics and, thus, mechanochemical outcomes.

  View details for DOI 10.1021/jacs.4c11912

  View details for PubMedID 39535496

• Tailoring Magnetism of Graphene Nanoflakes via Tip-Controlled Dehydrogenation. Physical review letters Zhao, C., Huang, Q., Valenta, L., Eimre, K., Yang, L., Yakutovich, A. V., Xu, W., Ma, J., Feng, X., Juricek, M., Fasel, R., Ruffieux, P., Pignedoli, C. A. 2024; 132 (4): 046201

  Abstract

  Atomically precise graphene nanoflakes called nanographenes have emerged as a promising platform to realize carbon magnetism. Their ground state spin configuration can be anticipated by Ovchinnikov-Lieb rules based on the mismatch of pi electrons from two sublattices. While rational geometrical design achieves specific spin configurations, further direct control over the pi electrons offers a desirable extension for efficient spin manipulations and potential quantum device operations. To this end, we apply a site-specific dehydrogenation using a scanning tunneling microscope tip to nanographenes deposited on a Au(111) substrate, which shows the capability of precisely tailoring the underlying pi-electron system and therefore efficiently manipulating their magnetism. Through first-principles calculations and tight-binding mean-field-Hubbard modeling, we demonstrate that the dehydrogenation-induced Au-C bond formation along with the resulting hybridization between frontier pi orbitals and Au substrate states effectively eliminate the unpaired pi electron. Our results establish an efficient technique for controlling the magnetism of nanographenes.

  View details for DOI 10.1103/PhysRevLett.132.046201

  View details for PubMedID 38335341