Dynamical decoupling of nitroxides in o-terphenyl: a study of temperature, deuteration and concentration effects

Abstract

We have characterized the temperature dependent transverse relaxation for 100 μM protonated and deuterated nitroxides in both protonated and deuterated o-terphenyl (OTP and dOTP) in distinct temperature regimes between 10 K and room temperature (RT). The choice of sample compositions allowed for a clear separation into slow and fast relaxation contributions based on a sum of two stretched exponential (SSE) parameterization between 10 and 60 K, and likewise at RT. The slow contribution is purely matrix dependent, while the fast process is determined by an interplay between a molecule and a matrix. Our systematic study of dynamical decoupling (DD) as a function of temperature (at 40, 80 K and RT), spin concentration, deuteration of nitroxide and/or OTP matrix and DD scheme for 1 to 5 refocusing pulses reveals that DD significantly prolongs phase memory times with respect to Hahn echo relaxation at 40 K, which we discuss in an SSE framework. At 80 K and RT, where (intra)molecular motions dominate relaxation, DD does not preserve electron spin coherence independent of the sample composition. Instead, we report a matrix nuclei dependent performance of the applied DD scheme at 40 K with Uhrig outperforming Carr-Purcell DD in OTP, and vice versa for a dOTP matrix.

Intermolecular background decay in RIDME experiments

“…A similar situation was observed earlier for nitroxide radicals and related to differences in intramolecular-and solvent-driven relaxation pathways. 55 In the present case, this finding might be attributed to the diversity of the local surrounding in the glassy matrix, as well as to the presence of several relaxation pathways. We thus conclude that in frozen glassy solutions, the relaxation data need to be described by a distribution of T m and T 1 times.…”

“…54 Note that in this work we used protonated PyMTA and the intramolecular interactions between the electron and the proton spins would still make an additional contribution to the electronic relaxation. 55 There is a clear concentration dependence of the shape of the transverse evolution decay for Gd-PyMTA. In a deuterated matrix, where the contribution by the electron-nuclear relaxation pathway is relatively weak, there is still a significant difference between the transverse relaxation curves measured at 100 mM and at 25 mM Gd-PyMTA concentration (Fig.…”

Counterion influence on dynamic spin properties in a V(iv) complex

“…Measurements were performed on 1 mM frozen solutions of 1–4 in o -terphenyl to minimize spin–spin interactions. We note that o -terphenyl is an under-explored solvent for pulsed studies yet affords three key advantages 48. First, it is a frozen glass at room temperature (melting point 58–59 °C; glass transition temperature at ca.…”

Storage and retrieval of microwave pulses with molecular spin ensembles

“…We first measure the phase memory time of diluted single crystal samples with the Hahn echo sequence and we then test two dynamical decoupling sequences: the Carr-Purcell-Meiboom-Gill (hereafter CP) sequence and the Uhrig Dynamical Decoupling (hereafter DD) sequence. These protocols are widely used to dynamically decouple the spins from environmental sources of decoherence and, hence, are expected to enhance T m [36][37][38][39] . Although the efficiency of CP and DD sequences has been previously investigated on spin impurities in inorganic matrices [40][41][42] and in organic molecules [43][44][45] (including radicals 39,46 ) coupled to conventional (3-dimensional) ESR cavities, their efficiency still needs to be tested on molecular spins in working conditions 1,21 .…”