An electron resonance investigation of molecular motion in the smectic A mesophase of a liquid crystal

Luckhurst, G. R.; Setaka, Morio; Zannoni, Claudio

doi:10.1080/00268977400101511

Cited by 91 publications

(37 citation statements)

References 27 publications

(43 reference statements)

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“…Dans le cas prCsent P4 (cos P') a kt6 dCduit de P2 (cos P') mesurk expCrimentalement en admettant que l'axe molCculaire A M effectue un mouvement alCatoire de iutation 2 l'intkrieur d'& cane centrC sur AL (Fig. 4) (16) ou que ce mouvement dipend d'un potentiel de la forme U(P1)/kT ---A sin' p' (17). Une Ctude en cours sur la dkpendance angulaire de la relaxation de "P dans le systkme NaDBP/H20 montre que ce second modkle rend le mieux compte des rksultats expkrimentaux, de sorte que nous l'avons Cgalement adopt6 pour le calcul des largeurs de raies des radicaux nitroxydes.…”

Section: Largeurs De Raiesunclassified

Orientation et dynamique moléculaire de sondes paramagnétiques en phase lamellaire dibutylephosphate de sodium/eau

Chachaty¹

1984

Can. J. Chem.

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R e~u le 24 mai 1983' C. CHACHATY. Can. J. Chem. 62, 1246Chem. 62, (1984. Les solutions aqueuses de dibutylephosphate de sodium (NaDBP) en concentrations de 3 a 4 mol L--' forment, entre 280 et 340 K , une phase cristalline liquide lamellaire. On Ctudie par rpe I'orientation ct la dynamique moltculaire dans cette phase, de sondes paramagnktiques telles que I'ion vanadyle et les radicaux nitroxydes, tempoamine, tempone et tempobutanamide.L'ion V02+ forme, avec le groupe phosphate, un complexe dont I'axe magnttique z est orient6 en moyenne selon la normale au plan lamellaire. La mobilitd moltculaire h i'interface entre les couches d'eau et de DBP-est donnCe par le temps de corrClation de nutation de I'axe z que I'on dtduit de la largeur totale du spectre par la relation empirique TR = a[I -(AII/Axx)I1'. Les parametres a = 2,95 X lo-" s et b = -1,42 sont dttermints par des mesures en fonction de la viscositd, des largeurs de raies et de l'anisotropie du couplage hyperfin de vO" La tempoamine et la tempone se localisent dans les domaines polaires de la mCsophase avec une reorientation rapide autour de la direction N-0 orientte en moyenne selon le directeur de la phase lamellaire. L'anisotropie de rkorientation de ces radicaux est attribuable selon les cas h la formation de liaisions hydrogene avec les groupes phosphates ou les molCcules d'eau interstitielles. On Ctablit quelques corrClations entre la rpe de ces sondes paramagnttiques et la rmn de ' H et "P des molCcules de substrat.C . CHACHATY. Can. J. Chem. 62, 1246 (1984). Aqueous solutions of sodium dibutylphosphate (NaDBP) give rise to lamellar liquid crystalline phase between 280 and 340 K for NaDBP concentrations ranging from 3 to 4 mol L-'. The orientation and dynamic behaviour of several paramagnetic probes such as the vanadyl ion, tempoamine, tempone and tempobutanamide dissolved in this phase have been investigated by esr.The vanadyl ion binds to the phosphate group, forming a complex. the z magnetic axis of which is on the average perpendicular to the lamellar plane. The molecular mobility at the H20/DBP-interface is given by the reorientation correlation time of the z axis, which is derived from the total width of the spectrum, using the empirical relation rR = a[1 -( A~~/ A~) ]~. The parameters a = 2.95 X lo-" s and b = -1.42 are obtained from the viscosity dependence of the esr line widths and of the anisotropic hyperfine couplings.The tempone and tempoamine are localized in the polar domains of the mesophase, reorienting rapidly about the N-0 direction which is, on the average, parallel to the director of the lamellar plane. The anisotropic motion of these radicals is assigned to hydrogen bonding which occurs, according to the cases, with water molecules or phosphate groups. Some correlations are established between the esr of spin probes and ' H and "P nmr experiments on substrate molecules.

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Section: Largeurs De Raiesunclassified

Orientation et dynamique moléculaire de sondes paramagnétiques en phase lamellaire dibutylephosphate de sodium/eau

Chachaty¹

1984

Can. J. Chem.

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“…We begin with the strong-collision model; the evaluation of the linewidth coefficients requires the order parameter P4 and this was calculated from the values for A s with the results given in table 5. This procedure contrasts with previous linewidth studies employing doublet states where the angular linewidth coefficients were employed to determine/~4 [3,4,7]. The components of the zero-field splitting tensor in the principal coordinate system, xyz, for the ordering tensor were found to be …”

Section: The Angular Linewidth Coefficientsmentioning

confidence: 97%

“…500 G.R. Luckhurst et al Nitroxide monoradicals are the most common spin probes and the theory needed to understand the linewidths of such doublet state species dissolved in anisotropic environments is well advanced [2][3][4][5]. Indeed it has been employed to considerable advantage in the study of membranes [5,6] as well as nematic [7] and smectic liquid crystals [4].…”

Section: Introductionmentioning

confidence: 99%

“…Consequently the spectrum of the spin probe may often exhibit a characteristic linewidth variation and, because of the anisotropic nature of the environment, this variation will depend on the sample orientation with resepct to the magnetic field. An understanding of such lincwidth effects is important not only as an aid to a correct spectral analysis but also because the linewidths contain valuable information relating to both the dynamic and static behaviour of the system [2][3][4]. 500 G.R.…”

Section: Introductionmentioning

confidence: 99%

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Spin relaxation for biradical spin probes in anisotropic environments

1975

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The large zero-field splitting of certain biradicals makes them important candidates for spin probes of anisotropic systems such as liquid crystals and membranes. The electron resonance spectrum of a biradical dissolved in a liquid crystal may be influenced by the zero-field splitting in two quite distinct ways. Firstly the line positions are affected because the spin probe is partially oriented by the liquid crystal solvent. In addition the zero-field splitting coupled with the molecular reorientation constitutes a powerful spin relaxation process and so may determine the widths of the spectral lines. Here we develop a theory of such line broadening, within the limit of fast motion, and show how it results in an angular dependence of the linewidths. The application of the theory is illustrated by studying the line broadening for a nitroxide biradical dissolved in a nematic mesophase. An analysis of the angular dependence of the linewidths suggests that the diffusion model provides a better account of molecular reorientation in a liquid crystal than the strong-collision approach. Finally we draw attention to the potential value of the theory for understanding the linewidth variations in the deuteron magnetic resonance spectra of liquid crystals.

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“…Application of continuous-wave (CW) EPR with spin probes to LCs has been pioneered in the group of Professor Geoffrey Luckhurst from the University of Southampton with the prominent contributions by Professor Claudio Zannoni who was the group member at the time. Their early papers established theoretical foundations for the analysis of the angular variation of EPR line shapes and spin relaxation of spin probes in anisotropic environments with applications to radical, biradical and triradical spin probes in LCs [1][2][3]. Later at the University of Bologna, Claudio continued to unravel the potential of EPR spectroscopy in LC research alongside other spectroscopic techniques.…”

Section: Introductionmentioning

confidence: 99%

EPR spectroscopy and molecular dynamics modelling: a combined approach to study liquid crystals

Oganesyan

2018

Liquid Crystals

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An electron resonance investigation of molecular motion in the smectic A mesophase of a liquid crystal

Cited by 91 publications

References 27 publications

Orientation et dynamique moléculaire de sondes paramagnétiques en phase lamellaire dibutylephosphate de sodium/eau

Orientation et dynamique moléculaire de sondes paramagnétiques en phase lamellaire dibutylephosphate de sodium/eau

Spin relaxation for biradical spin probes in anisotropic environments

EPR spectroscopy and molecular dynamics modelling: a combined approach to study liquid crystals

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