Short-lived excited triplet states studied by time-resolved EPR spectroscopy

Abstract

In this review, we present an overview of the application of time-resolved electron paramagnetic resonance (TREPR) to the study of excited triplet states. After a brief discussion of background and experimental methods, triplet properties clarified by TREPR are reviewed to show how TREPR provides rich information about electronic and molecular structures and dynamic properties of the lowest excited triplet states. The review includes discussion of the properties of non-phosphorescent triplet states, various interactions (configurational, vibronic and spin–orbit) and triplet properties, molecular distortions, and triplet states related to excited-state proton transfer. For each topic, typical examples are taken mainly from work carried out in the authors’ laboratories in Kyoto and Sendai over the last two decades. Finally, recent new advances are reviewed briefly by focusing attention on two topics: excited triplet states in liquid solution and multiplet excited states generated by triplet–radical interactions.