Photochromism of dihydroindolizines Part IX: First attempts towards efficient self-assembling organogelators based on photochromic dihydroindolizines and N-acyl-1,ω-amino acid units
Six new photochromic materials 9–11, 13–15 based on photochromic dihydroindolizine (DHI) system covalently linked to ester, acid or sodium N-acyl-11 aminoundecanoate through amidic or urethane linkage have been synthesized. These new compounds have been synthesized via nucleophilic addition of 11-methyl 4-pyridaizine aminoundecanoate 3 and methyl 11-methoxycarbonyl 4-pryradizine aminoundecanoate 6 to spirocyclopropene 1. Developing and tuning of the photophysical properties of the synthesized compounds by amide and urethane substitutes in the 4-position of the pyridazine base part have been achieved. The absorption maxima (λmax) and the half-lives (t1/2) of the colored betaines were detected in all cases using multichannel UV/vis spectrophotometric measurements. Irradiation of DHI 9, 10, 13 and 14 in CH2Cl2 solution at ambient temperature leads to the formation of red to red-violet colored betaines 8, 10′ 12 and 14′, respectively. The kinetics of the bleaching process of betaines back to DHIs were found to take place in the second range in dichloromethane solution (53–96 s) and fit well the first order thermal back reaction. Some of these DHIs showed a higher photostability than the standard one. Interestingly, they are shown to act as efficient gelators for polar organic fluids, and obviously they exhibiting a thermosensitive response as low molecular mass organogelators. In these fluids, the aggregative properties are totally suppressed upon conversion to neutral carboxylic species. The gels of these carboxylate sodium salts are shown to be markedly affected by light irradiation. Supramolecular gelating assemblies can be disrupted by the photoinduced ring opening of the chromene subunit, so that the macroscopic flowing property is recovered. Upon a further thermal treatment, the system is reversibly converted back to the supramolecular network. Controlled gelation could be achieved using temperature, light or acidity as external stimuli. These new synthesized photochromic gels with their multi-addressable properties will find their applications as photoresponsive materials and nanotechnology.
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 200, Issue 1, 15 November 2008, Pages 57–67