Sensitivity optimization in pulse EPR experiments with photo-labels by multiple-echo-integrated dynamical decoupling

Abstract

Photo-excited triplet states represent a new class of spin labels in pulse electron paramagnetic resonance (EPR), attracting increasing attention because of their unique spectroscopic properties. Despite certain advantages, the use of photo-labels has also some challenges, e.g. low repetition rates due to technical laser-related limitations and intrinsic properties of the labels. The application of additional pulse trains for multiple refocusing of the electron spin echo and integration of all observed echoes can significantly enhance sensitivity at a given repetition rate. In this work, we demonstrate that the use of Carr–Parcel–Meiboom–Gill (CPMG) blocks followed by multiple echo integration is a promising route for sensitivity gain in pulsed EPR utilizing photo-excited triplet states, including light-induced pulsed dipolar spectroscopy (LiPDS). The reduction of accumulation time by a factor of 5.3 has been achieved using a commercial pulsed EPR spectrometer with the implementation of a CPMG block and an external digitizer. The methodology of using CPMG refocusing with multiple echo integration in light-induced pulsed EPR experiments is discussed, aiding future applications of this approach in LiPDS experiments.