Influence of Pressure on the Intramolecular Spin Exchange in a Short Imidazolium-Nitroxide Biradical

Abstract

A short-chain imidazoline-type nitroxide biradical R₅^NO–CH=N–N=C(CH₃)–R₅^N, B2, with nitroxide rings R₅^N and R₅^NO as 1-oxyl-2,2,5,5-tetramethyl-3-imidazoline and 1-oxyl-2,2,5,5-tetramethyl-3-N-oxide imidazoline, respectively, has been studied using X-band electron paramagnetic resonance (EPR) spectroscopy in CH₃CN solutions at variable temperature T and pressure P. Changes of the solution viscosity on the intramolecular electron spin exchange in B2 is characterized by calculating the value of the exchange integral |J/a|, where a denotes the ¹⁴N hyperfine splitting (hfs) constant. It is revealed that the intramolecular dynamics in B2 do not follow the Debye–Stokes–Einstein law, while the Arrhenius dependence is fulfilled. Probable reasons of such behavior are discussed.