Supramolecular assembly of achiral alkynylplatinum(II) complexes and carboxylic β-1,3-Glucan into different helical handedness stabilized by pt⋯pt and/or π-π Interactions

Two-component ensembles of alkynylplatinum(II) terpyridine (tpy) complexes and carboxylic β-1,3-glucan (CurCOOH) have been investigated by using spectroscopic and microscopic techniques, as well as time-dependent UV/Vis absorption and circular dichroism (CD) experiments. Microscopic images of [Pt(tpy){CCC₆H₄(CH₂NMe₃-4)}](OTf)₂ (1) have revealed spherical nanostructures, whereas helical fibrous structures of different lengths, depending on the concentration of complex 1 and CurCOOH, were observed. The helical assemblies have been found to show low-energy metal-metal-to-ligand charge transfer (MMLCT) absorption and triplet MMLCT (³MMLCT) emission, which are indicative of Pt⋯Pt and/or π-π interactions between the complex 1 molecules. Interestingly, the ensemble has been demonstrated to show different handedness and even a change in handedness over time under different experimental conditions. Low temperatures, low concentrations of CurCOOH, high concentrations of complex 1, or successive addition of CurCOOH into complex 1 solution favor the formation of right-handed helical assemblies, whereas high temperatures, high concentrations of CurCOOH, low concentrations of complex 1, or single-batch addition of CurCOOH into complex 1 solution result in a fast chiroptical inversion of the ensemble solution, giving rise to the left-handed helical assemblies as the dominant species. The results have been rationalized by considering the competing kinetically and thermodynamically controlled assembly-elongation of the ensemble, which leads to the formation of right-handed and left-handed helical assemblies, respectively. The change in the handedness of the ensemble has been demonstrated to stem from the formation of two-component assemblies with supramolecular interactions, in contrast to the template- induced chiral amplification commonly observed in other systems. Two handed: Two-component ensembles of alkynylplatinum(II) terpyridine complexes and carboxylic β-1,3-glucan have been found to form supramolecular helical assemblies that are stabilized by Pt⋯Pt and/or π-π interactions (see figure). The systems show different handedness and even demonstrate a change in handedness over time under different experimental conditions. The results have been rationalized by considering the competing kinetic and thermodynamic assembly-elongation processes.