Ultrasound Assisted Co-aggregation of a Two-component System with Multicolor Emission and Its Response to Acid

In this paper, a two-component gel/micro-crystal system including amino acid and imidazole-based derivatives with blue and red emission, respectively, is designed and obtained. The two emission colors are convenient for the study of the co-aggregation of the two molecules via double channel confocal laser scanning microscopy. The two-component system could response to ultrasound with the morphology change from the mixture of club-shaped microcrystals and helical fibers by a thermal process to homogenous fibers exposing to sonication. Further evidence for the co-aggregation of the two components was obtained from circular dichromism (CD), IR spectra and X-ray powder diffraction. The self-assembly process between the two components was also studied by optimized molecular geometry calculation. Moreover, the co-aggregation obtained by the sonication then heating-cooling process, could not be destroyed by repeated heating-cooling. The gel-sol process could be further repeated for many times, suggesting that the co-aggregated gel was thermal-stable. It can be deduced that sonication weakened the intermolecular interaction between congeneric molecules and promoted the intermolecular hydrogen bonding between the two components. The results indicate that cooperation of the sonication and thermal processes is an effective way to prohibit phase separation and to promote gelation in the gel/micro-crystal system. Thus, a light harvest system is achieved by co-aggregation of the two components at nanoscale by means of sonication. The emission color of these two-component gels can be tuned by changing the ratio of the two compounds. These gels are sensitive to acid, giving clear spectral variation, accompanied by a gel to so! transition. The morphology of the two-component system is changed from a fiber structure to vesicles without phase separation when responding to acid and metal ions. Moreover, both the gel state and the morphology can be reversed by further addition of alkali. This kind of multifunctional and tunable two-component gel should have potential applications on the fields of visible molecular recognition, controllable release, stimulus responsive and memory materials.