Time-resolved EPR studies of excited states: Some old and some new stories

Abstract

An overview of the application of the time-resolved electron paramagnetic resonance EPR(TREPR) technique to the study of excited molecules is presented. The TREPR technique has been used very successfully to study short-lived triplet states of numerous molecules at low temperatures. Here after a brief introduction of the technique a few examples of such studies are discussed to show how TREPR provides rich information about electronic structures and dynamic properties ofexcited triplet states. The examples include elucidation of the electronic structures and dynamic properties of the lowest excited triplet states of some azaaromatic molecules, molecules related to excited state proton transfer and fullerenes. Exciting new advances have been made recently in the application of TREPR to the study of excited molecules. These include observation of excited triplet states in solution, detection of excited multiplet (quartet and quintet) states, and applications of Modem EPR techniques such as two dimensional nutation spectroscopy and W-band EPR. Some examples of such advances are also reviewed.