Kiryutin, Alexey S., Mikhail S. Panov, Alexandra V. Yurkovskaya, Konstantin L. Ivanov, and Geoffrey Bodenhausen. “Proton Relaxometry of Long-Lived Spin Order.” ChemPhysChem, January 2, 2019.
A study of long-lived spin order in chlorothiophene carboxylates at both high and low magnetic fields is described. Careful sample preparation (removal of dissolved oxygen in solution, chelating of paramagnetic impurities, reduction of convection) allows one to obtain very long-lived singlet order of the two coupled protons in chlorothiophene derivatives, having lifetimes TLLS of about 130 s in D2O and 240 s in deuterated methanol, which are much longer than the T1-relaxation times (18 and 30 s, respectively, at a field B0 = 9.4 T). In protonated solvents the relaxation times become shorter, but TLLS is still substantially longer than T1 . In addition, long-lived coherences are shown to have lifetimes TLLS as long as 30 s. Thiophene derivatives can be used as molecular tags to study slow transport, slow dynamics and slow chemical processes, as some of us have shown in recent years.