Regularized dynamical decoupling noise spectroscopy – a decoherence descriptor for radicals in glassy matrices

Abstract

Decoherence arises from a fluctuating spin environment, captured by its noise spectrum S(ω). Dynamical decoupling (DD) with n π pulses extends the dephasing time if the associated filter function attenuates...

Quantifying methyl tunneling induced (de)coherence of nitroxides in glassy ortho-terphenyl at low temperatures

“…It has been reported that classical rotation of tempone methyl groups gets slow on the ENDOR timescale below 80 K, 54 however, librations in general remain relevant below that temperature. 4 Moreover, the fast decaying contribution, which we attribute to methyl tunneling, 11 is not easily identifiable above 60 K, since the matrix-induced decoherence becomes very fast and a single stretched exponential suffices to fit the decay trace. This trend is also clearly visible in the extracted Gaussian rotation barrier distributions parameterized by V 3,av and σ shown in Fig.…”

“…where the matrix-induced decoherence is described by a stretched exponential function with phase memory time T m and stretched exponent ξ , based on assignment of this contribution to the slower of two stretched exponent terms in earlier work. 4,11 In the following we refer to this model as the methyl quantum rotor (MQR) model.…”

“…12,14 The faster contribution has only recently been attributed to methyl tunneling of the nitroxide's methyl groups by regularized noise spectroscopy. 11 A theoretical study predicted this effect for the two-pulse electron spin echo envelope modulation (ESEEM), i.e. Hahn echo, exa ETH Zurich, Laboratory of Physical Chemistry, Vladimir-Prelog-Weg 2, Zurich, Switzerland † Electronic Supplementary Information (ESI †) available: [details of any supplementary information available should be included here].…”

Intermolecular contributions, filtration effects and signal composition of SIFTER (single-frequency technique for refocusing)

“…Accordingly, each pulse sequence can be seen as a path for a (quasi-)decay of electron coherence due to the nuclei-related dephasing, and at the same time it can be seen as a filter function, selecting certain electron-nuclear frequencies and sup-pressing others. The latter process is often called dynamical decoupling (Soetbeer et al, 2021a). The first interpretation can also be seen as a type of filtering, albeit a different one: local nuclear configurations around electron spins might differ in the characteristic decay times, due to the strengths of the couplings or due to the different statistics of nuclear spinup and spin-down states.…”

Molecular dynamics and kinetics of isothermal cold crystallization with tunable dimensionality in a molecular glass former, 5′-(2,3-difluorophenyl)-2′-ethoxy-4-pentyloxy-2,3-difluorotolane

“…The molecular structure resembles o-terphenyl (OTP), the model glass-forming liquid, which is the subject of longstanding investigations. [45][46][47][48][49][50][51] OTP is broadly applied as a raw material for organic synthesis and pharmaceutical intermediate, and its derivatives are used in organic light-emitting diodes (OLEDs). [52][53][54] The chemically more complex molecule of DFP25DFT possesses polar groups and alkyl chains in alkoxy moieties that generally act as a trigger of crystallization.…”