Interspin Distances in a Triarylmethyl Biradical from Two-Pulse Electron Spin Echo

Triarylmethyl (TAM) radicals and TAM-based biradicals are often used as spin labels in different applications. Pulsed dipolar spectroscopy (PDS) is developed for studying interspin distances in the important nanoscale range. Here, we describe synthesis of bis-triarylmethyl biradical and its study using a simple PDS approach based on two-pulse electron spin echo (2p ESE) spectroscopy. It is shown that despite the well-known problems of dead time, interference of electron-nuclear interactions, and fast signal decay, this approach can provide reliable information for the interspin distances. In this approach, strong dipole-dipole coupling can be easily accounted for in the data analysis.