Determination of Hyperfine Coupling Constants of Fluorinated Diphenylacetylene Radical Anions by Magnetic Field-Affected Reaction Yield Spectroscopy

Abstract

Magnetic field-affected reaction yield (MARY) spectroscopy is a spin chemistry technique for detecting short-lived radical ions. Having sensitivity to transient species with lifetimes as short as nanoseconds, MARY spectroscopy usually does not provide detailed information on their magnetic resonance parameters, except for simple systems with equivalent magnetic nuclei. In this work, the radical anions of two fluorinated diphenylacetylene derivatives with nonequivalent magnetic nuclei and unknown hyperfine coupling constants (A HF) were investigated by MARY spectroscopy. The MARY spectra were found to be resolved and have resonance lines in nonzero magnetic fields, which are determined by the A HF values. Simple relationships between the positions of resonance MARY lines and the A HF values were established from the analysis of the different Hamiltonian block contributions to the MARY spectrum. The obtained experimental A HF values are in agreement with the results of quantum chemical calculations at the density functional theory level.

Recombination of X-ray-Generated Radical Ion Pairs in Alkane Solution Assembles Optically Inaccessible Exciplexes from a Series of Perfluorinated para-Oligophenylenes with N,N-Dimethylaniline

“…In the zero magnetic field, all four states are degenerate and the initially singlet pair is spread over all four states, and in a sufficiently high field, triplet states T + and T − are split away from singlet and T 0 by Zeeman interaction, and the initially singlet pair spreads over just two states out of the four, which increases the probability of its recombination in singlet state relative to the no-field case. This is certainly an oversimplification, and in reality, the situation can be much more interesting [110][111][112], especially for pairs comprising fluorinated radical anions often having very large hyperfine coupling constants [113][114][115][116], but this suffices to explain why an applied field of 200 Gauss, as used in this work, may be expected to change the intensity of emission.…”

Simple rules for resolved level-crossing spectra in magnetic field effects on reaction yields

“…where a k and n k are the HFC constants and spin projections for the kth nucleus. By the same token, an inhomogeneous spectrum, like a "semiclassical" Gaussian shape (Schulten and Wolynes, 1978), can be used in place of the sum k,n k a k n k . Substituting Eq.…”

Simple rules for resolved level crossing spectra in magnetic field effects on reaction yields

“…Several experimental reports of the resolved MARY spectra for systems with not equivalent nuclei with large HFC constants, in all cases fluorines, have been published. These include radical anions of 1,2,3-trifluorobenzene (Kalneus et al, 2007), pentafluorobenzene (Kalneus et al, 2006b), and recently several fluorosubstituted diphenylacetylenes (Sannikova et al 2019), again complemented with a radical cation having a narrow https://doi.org/10.5194/mr-2021-6…”