Time-resolved reaction yield detected magnetic resonance (RYDMR)

Radical Pairs in Solution

Radical pairs (RPs) are important reaction intermediates generated whenever two radicals encounter one another, a bond is cleaved homolytically or electron transfer between non-radical species takes place. The concept of a radical pair as a reaction intermediate is introduced and developed through simple pictorial analogies, indicating how RP behaviour is governed by interplay of spin and spatial motion. Such analogies are then extended to describe the experimental consequences of RPs in magnetic resonance and magnetochemistry experiments, including reference to the relevance of RPs in biological systems. Finally experimental techniques by which RPs can be observed directly are introduced and described in the context of the developed models.

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

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.

Theory of pulsed Reaction Yield Detected Magnetic Resonance

We propose pulse sequences for Reaction Yield Detected Magnetic Resonance (RYDMR), which are based on refocusing the zero-quantum coherences in radical pairs by non-selective microwave pulses and using the population of a radical pair singlet spin state as an observable. The new experiments are analogues of existing EPR experiments such as the primary echo, Carr-Purcell, ESEEM, stimulated echo and Mims ENDOR. All pulse sequences are supported by analytical results and numerical calculations. The pulse sequences can be used for more efficient and highly detailed characterization of intermediates of chemical reactions and charge carriers in organic semiconductors.