Synthesis And Self-assembly Of Linear Rod-like Platinum Gelators

Supramolecular gels are soft materials that consist of networks self-assembled from low molecular weight gelators through various noncovalent interactions. Metallogels, namely, gels with metallic species, benefit from the rich photophysical, magnetic and electronic properties while maintaining the stimuli-responsive and self-healing of supramolecular materials. Recently, metallogels have received many research interests. In this thesis, a series of linear rod-like gelators with trans-platinum(II) dichloride coordinated to mono pyridyl ligands were designed and synthesized. The gelating and self-assembly properties were studied successfully. As a comparison, the counterparts with palladium and no metal species were also prepared and studied. The main works in this dissertation are abstracted as follows:1. A series of gelators were designed and prepared by acylation and palladium catalyzed cross coupling reactions. They all share a linear rod-like shape with two terminal long alkyl tails. For a systematic study, molecules with different metal centers, linkages and ligands were all synthesized.2. Two structurally similar gelators which only differ in the metal center (platinum and palladium) were studied. In n-hexane, they both self-assembled into nanofibers as evidenced by TEM and SEM. The fibers entangled to form a network that immobilized the solvents. Noteworthily, a much lower critical gelation concentration of the platinum complex was observed. In the two xerogels, the platinum complexes stacked more tightly as revealed by WAXD. UV-Vis studies concluded that metallophilic interactions were incoorperated in the supramolecular polymerization process and the platinum complex showed a stronger interaction over the palladium counterpart. All the results have showed that trans-bis(pyridine) dichloropalladium(Ⅱ) and platinum(Ⅱ) complexes are effective moieties to construct metallogels, and the platinum complexes possess better noncovalent interactions and photophysical properties.3. Two linear rod-like platinum complexes with a larger conjugated ligand part were prepared, and they only differed in the linkage (ester and amide). They both self-assemble into metallogels in nonpolar solvents; however, a very big contrast was observed. Unexpectedly, a much weaker gel was acquired upon replacing the ester linkage by the amide group. Though TEM both showed nanofibers in the two diluted gels, the amide one adopted clear helical packings while the ester one gave straight and rigid bundles. Solvent and concentrations dependent UV-Vis spectra have revealed the stacking fashions and mechanisms. The amide molecules were fixed by the intermolecular hydrogen bondings and adopted a helical face to face (H-type) stacking fashion while the ester molecules formed slipped (J-type) aggregates. The supramolecular polymerization mechanism for the ester gelator is a highly cooperative one but the amide one follows an isodesmic model. The results contributed to the rational design of metallogels as well as other functional supramolecular materials.4. The linear conjugated molecules with no metal centers were prepared and their self-assembly and gelation properties were studied. The melt points were much lower compared to the metallic counterparts. The molecule with ester links could not gelate common solvents but nanofibers were observed when precipited from n-hexane, as revealed by TEM and SEM. The one with amide linkers could successfully form tolune gels with the additional intermolecular hydrogen bonding. By comparing the results with those of the platinum gelators, some advantages could be known. Though it does not merit the construction of thermotropic liquid crystals, the incorporation of platinum dichloride group is a good method to form supramolecular gels. Such platinum gelators self-assemble with different supramolecular packing style and mechanism. They also show richer spectroscopic properties. Similar to the linear alkyne-platinum gelators, trans-bis(pyridine) platinum dichloride is also a new and effective supramolecular construction group.All the results have concluded that linear trans-bis(pyridine) platinum dichloride complexes are well candidates for supramolecular chemistry. Our results are very important to metallo and π supramolecular self-assembly.