Photochromic Room Temperature Ionic Liquids Based on Anionic Diarylethene Derivatives

Abstract

Two photochromic room-temperature ionic liquids (RTILs) based on anionic diarylethene derivative (DTE) were synthesized and characterized. Photochemical (quantum yields for ring closure and opening) and electrochemical (cyclic voltammetry) properties of the [ALIQUAT] 2 [DTE] and [P 6,6,6,14 ] 2 [DTE] compounds as amorphous salts have been investigated. All compounds (including the di-acid precursor and two RTILs) were studied in solution, in their intrinsically pure forms (RTIL as unique media) and in the solid state (BaSO 4 support). Combination with larger organic cations can stabilize the closed-ring form, apparently avoiding the formation of by-products without photodegradation. It is observed that the closed-ring reaction is faster in the case of RTILs comparing to the di-acid starting material. The coloration switches between transparent (initial state) to purple ([ALIQUAT] 2 [DTE]) or pink ([P 6,6,6,14 ] 2 [DTE]). The novel diarylethene-based RTILs as multi-coloured photochromic materials can open attractive perspectives for materials science applications.

Chromic Ionic Liquids

“…Another popular chromophore that undergoes a reversible ring-opening/closing photoisomerization is diarylethene, , which can be regarded as a stilbene derivative and exhibits a blue-shifted absorption band in the closed form with reduced π-conjugation. After the initial work aimed at developing ILs using diarylethene-based cations (all salts have T m > 100 °C), diarylethene involving two anionic 2-thiophene­carboxylates as aryl moieties (Figure b) was utilized to build ILs by combining them with methyltri­( n -octyl)­ammonium (N 8,8,8,1 ; T g ∼ 0 °C) and P 14,6,6,6 ( T g ∼ −34.8 °C) cations . Transparent thin films of each open form exhibit purple and pink colors, respectively, by UV irradiation, and visible-light irradiation of the closed forms readily induces back-isomerization to produce the original open forms.…”

“…Opening/closing isomerizations in (a) spiropyran (closed)/merocyanine (open)-based monocation and (b) diarylethene-based dianion and (c) the transformation between the monomer and oligomer in a cyclopentadienyl–arene Ru­(II) complex monocation …”

Photoresponsive ion‐pairing assemblies

“…Pursuing a different approach, Branco et al synthesized ion pairs comprising a diarylethene dianion 9 2− , possessing two carboxylate groups situated at the thiophene α-positions (Figure 6b). [24] Two countercations, specifically (C 8 H 17 ) 3 CH 3 N þ and (C 6 H 13 ) 3 C 14 H 29 P þ , were employed in tandem with this dianion. The resulting ion pairs, 2 (C 8 H 17 ) 3 CH 3 N þ -9 2− and 2(C 6 H 13 ) 3 C 14 H 29 P þ -9 2− , exist as brown liquids at r.t., exhibiting the glass transition temperatures of 0.6 and −38°C, respectively.…”

Development of cellulose-based polymeric structures using dual functional ionic liquids

“…The selected synthetic methodology to prepare the desired ionic liquids consisted in two followed steps: (i) preparation of hydroxide form of the desired cation, through an anion exchange reaction using a ion exchange resin (Amberlyst A26 (OH)) [52][53][54] and, subsequently, (ii) acid-base reaction using the selected carboxylate acid (acetic, propanoic, hexanoic) as illustrated in Scheme 1. This methodology has the advantage to prepare halide-free ILs, contrarily to the conventional metathesis reaction, which produces inorganic salts as by-product.…”

“…The desired ionic liquids were synthesised according to an adapted synthetic procedure already reported in the literature, which avoid the formation of inorganic salts during the ILs synthesis. [52][53][54][55] The ion-exchange resin, Amberlyst A26 (OH) (ca. 1.5 equivalents) was added to the halide salt of the desired cation ([BE]Cl or [DDA]Br, ca.…”