Chapter One - Time-Resolved Electron Paramagnetic Resonance Spectroscopy: History, Technique, and Application to Supramolecular and Macromolecular Chemistry
The experimental technique of time-resolved (direct detection) electron paramagnetic resonance (TREPR) spectroscopy, and its role in the elucidation of free-radical structure, dynamics, and reactivity within the field of “spin chemistry,” is presented and discussed. Significant detail regarding the construction and execution of the experiment, which requires only minor modification of a commercial electron paramagnetic resonance spectrometer, is provided for the first time. Special requirements for the resonator, sample geometry, light source, timing sequences, and all additional required equipment are explained. Chemically induced electron spin polarization (CIDEP) mechanisms (radical pair mechanism (RPM), triplet mechanism, spin–correlated radical pair (SCRP) mechanism, and radical-triplet (RT) pair mechanism), which are commonly observed in this experiment, are briefly described in terms of their physical origin and their unique spectral appearance. Finally, examples of the use of TREPR in the study of modern problems in supramolecular and macromolecular chemistry are presented. These examples, which include the effect of electrostatics on the behavior of micellized radical pairs and the role of RT pairs in the study of polymer chain dynamics in the dilute condition, are selected because they contain particularly clear examples of each CIDEP mechanism.