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Issue 10, 2019
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Living in the salt-cocrystal continuum: indecisive organic complexes with thermochromic behaviour

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Abstract

A family of multicomponent haloaniline/3,5-dinitrobenzoic acid molecular crystals with striking red-to-colourless temperature-induced thermochromism is identified and characterised. Four thermochromic pairs of 1 : 1 neutral cocrystals and ionic salts are identified which, unusually, grow concomitantly under the same conditions. The coloured cocrystals are found to be metastable, kinetically trapped during crystallisation, and convert via proton transfer to the more stable salt forms on heating. The colour of the neutral form and the temperature of the transition can be tuned through the halogen and by chemical substitution on the aniline component. From structural characterisation and first-principles modelling, we elucidate the origin of the metastability of the cocrystals and link structural changes through the phase transition to the striking visible colour change. By deliberately exploiting the uncertainty of the salt-cocrystal continuum, where the small pKa difference between components enables significant solid-state structural rearrangements induced by proton transfer, this work highlights a novel design paradigm for engineering new organic thermochromics with tailored physical properties.

Graphical abstract: Living in the salt-cocrystal continuum: indecisive organic complexes with thermochromic behaviour

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Publication details

The article was received on 05 Dec 2018, accepted on 07 Feb 2019 and first published on 07 Feb 2019


Article type: Paper
DOI: 10.1039/C8CE02066C
Citation: CrystEngComm, 2019,21, 1626-1634
  • Open access: Creative Commons BY license
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    Living in the salt-cocrystal continuum: indecisive organic complexes with thermochromic behaviour

    C. L. Jones, J. M. Skelton, S. C. Parker, P. R. Raithby, A. Walsh, C. C. Wilson and L. H. Thomas, CrystEngComm, 2019, 21, 1626
    DOI: 10.1039/C8CE02066C

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