Dimensional Control and Morphological Transformations of Supramolecular Polymeric Nanofibers Based on Cofacially-Stacked Planar Amphiphilic Platinum(II) Complexes

• Published in: ACS nano Vol. 11; no. 9; pp. 9162 - 9175
• Main Authors: Robinson, Matthew E, Nazemi, Ali, Lunn, David J, Hayward, Dominic W, Boott, Charlotte E, Hsiao, Ming-Siao, Harniman, Robert L, Davis, Sean A, Whittell, George R, Richardson, Robert M, De Cola, Luisa, Manners, Ian
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 26.09.2017
• Subjects: seeded growth; supramolecular polymers; self-assembly; kinetic control; living supramolecular polymerization
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.7b04069

Square-planar platinum­(II) complexes often stack cofacially to yield supramolecular fiber-like structures with interesting photophysical properties. However, control over fiber dimensions and the resulting colloidal stability is limited. We report the self-assembly of amphiphilic Pt­(II) complexes with solubilizing ancillary ligands based on polyethylene glycol [PEG n , where n = 16, 12, 7]. The complex with the longest solubilizing PEG ligand, Pt-PEG 16 , self-assembled to form polydisperse one-dimensional (1D) nanofibers (diameters <5 nm). Sonication led to short seeds which, on addition of further molecularly dissolved Pt-PEG 16 complex, underwent elongation in a “living supramolecular polymerization” process to yield relatively uniform fibers of length up to ca. 400 nm. The fiber lengths were dependent on the Pt-PEG 16 complex to seed mass ratio in a manner analogous to a living covalent polymerization of molecular monomers. Moreover, the fiber lengths were unchanged in solution after 1 week and were therefore “static” with respect to interfiber exchange processes on this time scale. In contrast, similarly formed near-uniform fibers of Pt-PEG 12 exhibited dynamic behavior that led to broadening of the length distribution within 48 h. After aging for 4 weeks in solution, Pt-PEG 12 fibers partially evolved into 2D platelets. Furthermore, self-assembly of Pt-PEG 7 yielded only transient fibers which rapidly evolved into 2D platelets. On addition of further fiber-forming Pt complex (Pt-PEG 16 ), the platelets formed assemblies via the growth of fibers selectively from their short edges. Our studies demonstrate that when interfiber dynamic exchange is suppressed, dimensional control and hierarchical structure formation are possible for supramolecular polymers through the use of kinetically controlled seeded growth methods.