Photochromic imidazolium based ionic liquids based on spiropyran

Abstract

We investigate the photo, solvate and thermochromic properties of a novel photoswitchable spiropyran derivative; SP Im in imidazolium based ionic liquids (ILs). SP Im was prepared by alkylation of the photoswitchable compound to an imidazolium cation and is added to imidazolium based ILs with increasing chain length to examine the stability of funtionalised cations its merocyanine (MC) and spiropyran (SP) forms and compared to standard spiropyran; BSP. The rate of thermal relaxation of the new derivative is found to be about ten times faster than that of BSP as reflected in rates of 13.9 x10 -3 s -1 and 1.0 x10 -3 s -1 for SP Im and BSP respectively in [C 6 mIm][NTf 2 ]. Since ILs are believed to form nano-structured domains it is proposed that the covalent attachment of the imidazolium side group of SP Im fully integrates the photoswitchable moiety into the non-polar region through side-chain association. In contrast, unbound BSP is relatively free to migrate between both polar and non-polar regions and the MC form is more readily stablised by the IL charge via through space interactions and spontaneous movement to charged nano-domains leading to enhancement of the MC lifetime. At higher concentrations, rheological and transport properties were investigated to determine the impact of covalent attachment of the BSP fragment to an imidazolium cation had upon the ionic liquid structure. Ionic Conductivity was found to decrease by up to 23% for SP Im with effects increasing with cation side-chain length. Unlike BSP, the photoswitching of the SP Im did not affect conductivity or viscosity values. This may indicate that the mobility of the photoswitchable compound and the resulting disruption of such movement may be critical to the evolution of this physical property.2

Atom transfer radical polymerization synthesis and photoresponsive solution behavior of spiropyran end‐functionalized polymers as simplistic molecular probes

“…The entropy of activation Δ S ± is a measure of the amount of reorientation of the system during the thermal relaxation from BMC‐PMMA to BSP‐PMMA and is related to degrees of freedom lost or gained from the aforementioned system. The positive Δ S ± values for both polymers indicate that when the BMC end‐group reverts to the BSP form, it gains degrees of freedom, for example, by solvation 40. The higher Δ S ± value of 63.47 J K −1 mol −1 for the higher molecular weight polymer indicates a more significant gain for this polymer.…”

DyeIonogels: Proton‐Responsive Ionogels Based on a Dye‐Ionic Liquid Exhibiting Reversible Color Change

“…One issue to overcome is the limited solubility of many active components such as dye molecules in ILs. There is thus a need to develop highly soluble active components, but so far, there are only a few examples . In this contribution, we therefore describe a new approach towards responsive ionogels exhibiting a reversible color change.…”

Hydroxyethylcellulose‐graft‐poly(2‐(dimethylamino)ethyl methacrylate) as physically adsorbed coating for protein separation by CE

“…Since their discovery, photochromic SPs have been incorporated into various materials, i.e., surface bound monolayers,7, 11–13 Langmuir monolayers,14 Langmuir‐Blodgett films,14 polymeric brushes,9, 15–17 photocontrollable surfactants,18 liquid crystalline materials,19 polymeric matrices,8, 15, 16, 20–36 organic/inorganic hybrid systems,37 colloidal particles,17, 38 ionic liquids (ILs)39–43 and initiators for radical polymerisations 44…”