Viologen-based ionic liquid crystals: induction of a smectic A phase by dimerisation

Casella, Girolamo; Causin, Valerio; Rastrelli, Federico; Saielli, Giacomo

doi:10.1039/c3cp54628d

Cited by 51 publications

(45 citation statements)

References 23 publications

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“…[10][11][12] Redox active liquid crystals, without any ionic function, do not show electrochromism in the bulk state but only in electrolyte solutions. [16][17][18] Viologen-based liquid crystals deserve particular attention and a wide range of their derivatives were synthesized showing either the smectic [19][20][21][22] or columnar 23,24 phase. Bipyridinium salts, also known as viologens, are the most famous electrochromes, used as cathodic colouring components in EC devices.…”

Section: Introductionmentioning

confidence: 99%

Mesomorphism and electrochemistry of thienoviologen liquid crystals

Cospito

Beneduci

Veltri

et al. 2015

Phys. Chem. Chem. Phys.

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The thienoviologen series 4,4'-(2,2'-bithiophene-5,5'-diyl)bis(1-alkylpridinium)X2, with = counterion is a new class of electron acceptor materials which show very interesting electrochromic and electrofluorescence properties. Depending on the length, m, of the promesogenic alkyl chains, and on the counterion, thienoviologens might become liquid crystals. Here, we present the mesomorphic behaviour, and the electrochemical and spectroelectrochemical properties in solution of new thienoviologens of the series and (I = iodide; NTf2(-) = bis(tri-fuoromethylsulfonyl)imide) with m = 8, 12. Interestingly, we found that only the compounds are liquid crystals, exhibiting a calamitic behaviour in contrast to the homologous compounds of the series with m = 9-11 and X = NTf2(-), which showed columnar rectangular mesophases. The electrochemical study here reported allowed us to explain for the first time the anomalous behaviour of these thienoviologens already observed in cyclic voltammetry, where two apparently irreversible redox processes occur. This can be explained by a comproportionation reaction in which the neutral species rapidly reduces the dication to the radical-cation, due to its strong reducing power. Electrochemical reduction of the thienoviologens causes electrochromism since a new absorption band, occurring at 660 nm in the electronic spectra, appears with the negative potential bias applied. With a LUMO level of 3.64 eV, similar to those of the C60 and of other n-type materials, these compounds can find applications in several electronics devices, where their liquid crystalline properties can be used to control film morphology and geometry, provided they have good electron mobility.

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Section: Introductionmentioning

confidence: 99%

Mesomorphism and electrochemistry of thienoviologen liquid crystals

Cospito

Beneduci

Veltri

et al. 2015

Phys. Chem. Chem. Phys.

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“…[24][25][26] The dication bipyridinium salts are consideredt ob erod-like molecules with high structural similarity and at endency to form ILCs. [16,[27][28][29][30] From DSC analysis, it seems that the prepared salts containing [(C 10 )bpy(C 4 O)bpy(C 10 )][NTf 2 ]f orm ILC structures. As proof of this, an additional DSC experiment was performed between 25 to 250 8C( Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

Bis(bipyridinium) Salts as Multicolored Electrochromic Devices

Jordão

Cruz

Branco³

et al. 2017

ChemPlusChem

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Symmetrical and nonsymmetrical oxobis(bipyridinium) cations combined with iodide and bistriflimide anions were prepared. In the case of the bistriflimide‐based bis(bipyridinium) salts, two room‐temperature ionic liquids (RTILs) with a combination of linkers and terminal ethers, [(C3O)bpy(C4O)bpy(C3O)][NTf2]4 and [(C10)bpy(C4O)bpy(C3O)][NTf2]4, were obtained, with glass transition temperatures (between −6.9 and 6.0 °C) higher than those reported previously for salts of dication bipyridinium scaffolds (−17.5 to −30.0 °C). The prepared salt containing [(C10)bpy(C4O)bpy(C10)][NTf2] can form an ionic liquid crystal structure. The most promising salts were tested as efficient and reversible multicolored electrochromic devices through cyclic voltammetry studies and detailed characterizations of their electrochromic performances. In general, tetracations based on oxobis(bipyridinium) salts show higher chromatic contrast and lower coloration efficiency than similar dication salts. Exchange of the anion from iodide to [NTf2] increases the transition times and coloration efficiencies for all the prepared di‐ and tetracation salts. The electrochromic device stability of [(C3O)bpy(C4O)bpyC3O]I4 was tested by on/off cycling; this device loses around 23 % of the initial color after 8640 redox cycles and shows very good cycling stability compared with previously reported diiodide salts.

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“…Most reported ILCs contain single organic cation unit in one ILC molecule. Recently, ILCs containing multiple imidazolium units are reported by Schenkel, which can exhibit smectic A phase [29]; and viologen-based ILCs with bipyridinium cores are reported by Casella, which exhibit rich polymorphism including the ionic smectic A phase and an ordered smectic phase [30]. In particular, imidazolium-based ionic liquids attract considerable attention among these types of ILCs because they give low melting points with high chemical and electrochemical stability, and exhibit excellent ability in anisotropic ionic conductivity, organized reaction media or ordered solvents [31,32].…”

Section: Introductionmentioning

confidence: 99%