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Updated: Oct 14, 2025

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
Spinning Molecules, Spinning Spins: Modulation of an Electron Spin Exchange Interaction in a Highly Anisotropic
Alexander M Brugh1, Ruobing Wang2, Michael J Therien2
1Center for Photochemical Sciences, Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States.
Abstract:
An investigation of spin and conformational dynamics in a series of symmetric Cu-Cu porphyrin dimer solutions is presented using electron paramagnetic resonance (EPR) spectroscopy. Previous spectral simulations focused on the isotropic exchange interaction (J avg) between the Cu centers. In this work, an additional line broadening parameter (J mod) is explored in detail via variable temperature X-band EPR in liquid solution for several different structures. The J mod phenomenon is due to fluctuations in the spin exchange interaction caused by conformational motion of the porphyrin planes. The J mod parameter scales with the inverse of the rotational barriers that determine the Boltzmann-weighted torsional angle distribution between neighboring porphyrin planes. Arrhenius plots allow for extraction of the activation energies for rotation, which are 5.77, 2.84, and 5.31 kJ/mol for ethyne-bridged (porphinato)copper(II)-(porphinato)copper(II), butadiyne-bridged (porphinato)copper(II)-(porphinato)copper(II), and ethyne-bridged (porphinato)copper(II)-(porphinato)zinc(II)-(porphinato)copper(II) complexes, respectively. DFT calculations of these torsional barriers match well with the experimental results. This is the first report of a J mod analysis within a highly anisotropic hyperfine field and demonstrates the utility of the theory for extraction of dynamic information.
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