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EPR studies of the dynamics and phase behaviour of dithiadiazolyl radicals derived from mesogenic precursors

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JournalMAGNETIC RESONANCE IN CHEMISTRY
DatePublished - Jan 2009
Issue number1
Volume47
Number of pages6
Pages (from-to)38
Original languageEnglish

Abstract

A series of liquid-crystalline materials based on 4-substituted cyanobiphenyls, RC6H4C6H4CN (R = C5H11, C6H13, C7H15, C8H17 and C12H25, commonly referred to as 5CB, 6CB, 7CB, 8CB and 12CB, respectively) were functionalised to give the corresponding dithiadiazolyl organic radicals RC6H4C6H4CNSSN* (compounds 1(center dot), 2(center dot), 3(center dot), 4(center dot)and 5(center dot), respectively). EPR spectra of n-C12H25C6H4C6H4CNSSN center dot (5(center dot)) reveal that it adopts a dimeric diamagnetic structure in the solid state with a small number of paramagnetic defect sites. Variable temperature electron paramagnetic resonance (EPR) studies reveal a thermally activated rotation about the molecular long axis at temperatures above 314 K. The energy barrier to rotation about the phenylene-dithiadiazolyl bond was estimated as 25 kJ mol(-1) using density functional theory (DFT). At elevated temperatures thermal annealing was also observed, quenching the sample's paramagnetism. Copyright (C) 2008 John Wiley & Sons, Ltd.

    Research areas

  • electron spin resonance, electron paramagnetic resonance, dithiadiazolyl, thiazyl, heterocyclic free radical, liquid-crystalline, pi-radical, free radical, ELECTRON-SPIN-RESONANCE, NEMATIC LIQUID-CRYSTALS, SOLID-STATE STRUCTURES, MAGNETIC-PROPERTIES, SPECTROSCOPY, PERSISTENT

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