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

Abstract

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){C≡CC6 H4 (CH2 NMe3 -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 ((3) MMLCT) 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.

Recent Advances in Phosphorescent Pt(II) Complexes Featuring Metallophilic Interactions: Properties and Applications

“…Another example of supramolecular self-assembly of chiral structures has been reported by Yam and co-workers 56 who have shown how achiral alkynylplatinum(II) complexes can interact with carboxylic β-1,3-glucan motifs leading to chiral helicoidal structures (complex 6 in Chart 1). Interestingly, the handedness of this two-component helical assembly is affected by different parameters such as temperature, aging, components ratios, and mode of preparation and was tentatively rationalized in terms of kinetic vs. thermodynamic control.…”

Conjugated Polyelectrolyte‐Induced Self‐Assembly of Alkynylplatinum(II) 2,6‐Bis(benzimidazol‐2′‐yl)pyridine Complexes

“…6e, 7, 8d Extension of the work to the design of systems which self‐assemble into supramolecular architectures, for example metallogels,4b,c, 6b, g and molecular architectures like nanostructures,6d–f, 7b hairpin structures,6a,b helices,3 and molecular tweezers,8 has also been made. Recently, our group has demonstrated the self‐assembly of cationic alkynylplatinum(II) terpyridine complexes induced by the electrostatic interactions with polyanionic synthetic polyelectrolytes9a–d, 10 and biopolymers such as single‐stranded nucleic acids, aptamers, heparin and carboxylic curdlan,9e–g,k which shows remarkable UV/Vis absorption and near‐infrared (NIR) emission spectral changes. Label‐free detection and quantification of various biologically important macromolecules, including their conformational changes and enzymatic activities, can be achieved through the exploitation of such significant spectral changes arising from the assembly‐disassembly behavior of the platinum(II) complexes 9d–j.…”

Helical-Ribbon and Tape Formation of Lipid Packaged [Ru(bpy)3]2+ Complexes in Organic Media

“…Moreover, the assembly of metal complexes has been suggested as a basis for forming molecular device system such as biodiagnostics, photovoltaics, and organic light-emitting diodes [18,19]. Ideally, the characteristics of such systems would be tunable by controlling the spatial arrangement of the metal complexes, resulting in optical interaction among metal complexes with linkage of weakly non-covalent interaction such as hypochromic effect [20], aromatic interaction [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37], metallophilic interaction [38,39,40,41,42,43,44,45,46,47,48], and so on.…”