Binary organogelators which show light and temperature responsiveness

Abstract

The gelation ability of 10 alkylammonium (CnH(2n+1)NH3+ where n=4-11, 12 and 16) anthracene-9-carboxylates (1n) has been evaluated. In cyclohexane, 1(4), 1(5), 1(6) and 1(7) only provided precipitates whereas 1(11), 1(12) and 1(16) provided very viscous solutions. In contrast, 1(8) 1(9) and 1(10) resulted in gels. The critical gelation concentration of 1(10) was very low (5.0 x 10(-4) mol dm(-3)). SEM observations showed that in the gel phase the morphology changes from straight fibrils to frizzy fibrils with the increase in n, whereas in the sol phase the formation of the sheet-like, two-dimensional aggregate is recognized. When the cyclohexane 1(10) gel was photoirradiated (lambda > 300 nm), the UV-VIS absorption bands assignable to monomeric anthracene were decreased and the gel was changed into the sol. It was confirmed by dark-field optical microscopy that the fibrillar bundles supporting the gel formation gradually disappear with photoirradiation time. When this sol was warmed at 30 degrees C in the dark, the gel was not regenerated but the precipitation of 1(10) resulted. When this sol was heated once at the bp of cyclohexane and cooled to 15 degrees C, the solution was changed into the gel again. This finding indicates that the fibrillar structure required for the gel formation is not reconstructed at 30 degrees C but obtained only when the hot cyclohexane solution is cooled.

Photoinduced Crystallization in Ionic Liquids: Photodimerization-induced Equilibrium Shift and Crystal Patterning

“…20 It is also considered that the dimers D-2COOH form hydrogen bonding with two carboxylic acid groups of the neighboring photodimers, which promote segregation of the crystals in IL. It is to note that the photodifferentiation phenomenon found in this study has not been reported for the previous [4+4] cycloaddition reaction of anthracene carboxylic acids in organogels, 12,21 liquid crystals, 22,23 and ionic liquids, 24,25 probably due to the presence of organic solvents or the use of 2-anthracenecarboxylate, whose pK a is less influenced by photodimerization.…”

“…11 Here, we describe a new photoresponsive IL that shows photoinduced crystallization phenomena. It is formed from a well-known Brønsted acid (9-anthracenecarboxylic acid, A-COOH) 12 (Figure 2a and Scheme S1, SI). The chemical composition and purity of the IL was confirmed by elemental analysis and 1 H NMR spectra ( Figure S1, SI).…”

Two‐Component Gel‐Phase Materials—Highly Tunable Self‐Assembling Systems

“…[20] Interestingly, this system, in addition to being thermally responsive, was also responsive to light. The two-components were anthracene-9-carboxylate (photo-responsive unit) and an alkylammonium group (the structuring unit).…”

Supramolecular Gels: Functions and Uses

“…7 Upon irradiation with a mercury lamp, the gel in cyclohexane at 15 uC transformed into a sol via photo-induced dimerization of the anthracene units leading to a non-gelator. However, warming this sol to 30 uC in the dark thermally dissociates the anthracene dimer, and the gelator is regenerated which leads to a precipitate.…”