Fig. 2. Experimental (a, b) and simulated (c, d) MAS frequency dependence of εon/off (left axis, black), εB (left axis, red), and χdepo (right axis, blue) for trityl-nitroxide (a, c) and nitroxide–nitroxide (b, d) based biradicals. Nuclear polarization was determined via the 1H signal integral. The μw frequency was 263.67 GHz and the magnetic field set to the position giving maximum 1H signal intensity. Experimental data from Mentink-Vigier et al.48 is reproduced here in (b) as a comparison to the data in (a). Definitions for εon/off, εB, and χdepo and. the biradical geometry are given in the Materials and method, For trityl-nitroxide Ja,b/2π = 30 MHz, Da,b/2π = 23 MHz, and for AMUPol, Ja,b/2π = 15 MHz and Da,b/2π = 35 MHz.
