Time-resolved (CW) electron paramagnetic resonance spectroscopy: An overview of the technique and its use in organic photochemistry

Steady-state and time-resolved electron paramagnetic resonance (TREPR) experiments are described, Comparison of the TREPR continuous wave method to other time domain EPR techniques such as Fourier transform EPR (FT-EPR) is made, and the advantages and disadvantages of each are presented, The role played by several mechanisms of chemically induced dynamic electron spin polarization (CIDEP) in the appearance of the spectra is explained. The advantages of using higher frequency spectrometers than the standard X-band (9.5 GHz) are presented and discussed. Examples are presented that are relevant to organic photochemistry and electron donor-acceptor chemistry, The use of TREPR to study polymer photodegradation, polymer chain dynamics, free radical initiator chemistry and biradical spin exchange interactions is described. Emphasis is placed on magnetic field effects studied by multiple frequency TREPR in these systems. Finally, several future directions in the field are discussed in terms of new developments in microwave and magnetic field technology.