Time-Resolved Electron Paramagnetic Resonance Spectroscopy

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Generally, there are different ways of detecting transient spin-polarised paramagnetic species with EPR. Probably the most common is to use a conventional cw-EPR spectrometer in a direct detection mode – such as not to restrict the achievable time resolution – and recording transients.

Figure 1: Schematic diagram of an EPR spectrometer for conventional continuous-wave and time-resolved measurements. The basic setup is identical in both cases. The sample is placed in a cavity (resonator) situated between the poles of the magnet. Microwave is fed into the cavity from a microwave source (MW source), and the microwave reflected is directed toward the detector by means of a circulator. For cw-EPR spectroscopy, a lock-in detection scheme is used for enhanced signal-to-noise ratio, comprising of additional modulation coils placed on the inside of the poles of the magnet, modulating the external magnetic field. The signal is detected phase-sensitive with respect to this external modulation. Typical modulation frequencies are in the range of 10–100 kHz, thus restricting the available time resolution technically to several tens of microseconds, whereas in practice, most spectrometers only allow a lower limit of about a millisecond. Due to the non-Boltzmann population of the energy levels of spin-polarized paramagnetic states created by light excitation through a pulsed light source, signals can be detected in a direct manner in TREPR spectroscopy, meaning excluding lock-in detection. This allows for a much higher time resolution down to a few nanoseconds. Taken from: Biskup, Till (2019): Structure–function relationship of organic semiconductors: Detailed insights from time-resolved EPR spectroscopy. Frontiers in Chemistry 7:10. doi: 10.3389/fchem.2019.00010

In principle, it is possible to use pulsed EPR techniques as well to obtain spectra of transient polarised species.


  • Biskup, Till (2019): Structure-function relationship of organic semiconductors: Detailed insights from time-resolved EPR spectroscopy, Frontiers in Chemistry 7:10
  • Forbes, Malcolm D.E.; Jarocha, Lauren E.; Sim, SooYeon; Tarasov, Valery F. (2013): Time-resolved electron paramagnetic resonance spectroscopy: History, technique, and application to supramolecular and macromolecular chemistry, Advances in Physical Organic Chemistry 47:1-83
  • Weber, Stefan (2017): Transient EPR, eMagRes 6:255-270
experiment/index.txt · Last modified: 2019/06/15 10:12 by till