Margaret Ching-Lam Yeung

Towards thermochromic and thermoresponsive near-infrared (NIR) luminescent molecular materials through the modulation of inter- and/or intramolecular Pt⋯Pt and π–π interactions

A series of mononuclear and dinuclear alkynylplatinum(II) terpyridyl complexes has been found to show inter- and/or intramolecular aggregation in fluid solution state at low temperature or even at room temperature. Drastic colour changes and near infra-red (NIR) emission enhancement as well as broad and poorly resolved resonance signals in the 1H NMR spectra were observed. Such aggregation processes have been probed by 1H NMR, electronic absorption and emission spectroscopy.

Phosphate derivative-induced supramolecular assembly and NIR-emissive behaviour of alkynylplatinum(II) terpyridine complexes for real-time monitoring of enzymatic activities

Polyanionic phosphate derivatives, ATP and phosphopeptide, were shown to induce the supramolecular assembly of cationic alkynylplatinum(II) terpyridine complexes via the formation of metal–metal and π–π stacking interactions with significant UV-vis, near-infrared (NIR) emission and circular dichroism spectral changes. The induced supramolecular assembly behaviours of these platinum(II) complexes were shown to be sensitive towards microenvironmental changes as well as the negative charge densities of the phosphate derivatives, providing the complexes with the capability of distinguishing the target substrates from their respective metabolic products by sole structural differences. Through the monitoring of the NIR emission spectral changes that are dependent on the extent of the assembly/disassembly of the platinum(II) complexes, the conversion of the target substrates catalyzed by ATPase, v-Src kinase and alkaline phosphatase could be signaled and probed on a real-time basis. The kinetic parameters of the enzymatic activities have also been determined.

Assembly of Heterometallic Silver(I)–Copper(I) Alkyl-1,3-diynyl Clusters via Inner-Core Expansion

New tetranuclear supramolecular precursors [(R-C≡C-C≡C)Ag]4 (R = iPr, tBu, and chx) are employed to construct a series of heterometallic silver(I)-copper(I) alkyl-1,3-diynyl cluster complexes (1-9) that bear a common CuAg3 core (normally trigonal-planar, but can be distorted to pyramidal) consolidated by cupro-argentophilic interaction under 3.12 Å, as found in 1 and 2. The photophysical properties of the multinuclear supramolecular precursors and selected complexes have been investigated. The present results strongly suggest that the assembly of medium-nuclearity clusters 3 to 9 is initiated by accretion of additional Ag(I) ions by the ubiquitous CuAg3 template through argentophilic (<3.4 Å) interaction, with cooperative cuprophilic enhancement (<2.76 Å) in the case of compound 9. To our knowledge, the present study provides the first report of conversion of a Group 11 homonuclear cluster into a heteronuclear one of higher nuclearity via inner-core expansion.

Anion Binding Properties of Alkynylplatinum(II) Complexes with Amide-Functionalized Terpyridine: Host–Guest Interactions and Fluoride Ion-Induced Deprotonation

Molecular sensors able to detect ions are of interest due to their potential application in areas such as pollutant sequestration. Alkynylplatinum(II) terpyridine complexes with an amide-based receptor moiety have been synthesized and characterized. Their anion binding properties based on host–guest interactions have been examined with the use of UV-vis absorption and emission spectral titration studies. Spectral changes were observed for both complexes upon the addition of spherical and nonspherical anions. Their titration profiles were shown to be in good agreement with theoretical results predicting a 1:1 binding model, and the binding constants were determined from the experimental data. Drastic color changes from yellow to orange–red were observed for one of the complexes upon titration with fluoride (F−) ion in acetone. These changes were ascribed to the deprotonation of the amide functionalities induced by F− ion, and this was confirmed by the restoration of spectral changes upon addition of trifluoroacetic acid to the F− ion–complex mixture as well as by electrospray ionization mass spectrometry (ESI-MS) data.

Molecular Engineering of Platinum(II) Terpyridine Complexes with Tetraphenylethylene-Modified Alkynyl Ligands: Supramolecular Assembly via Pt···Pt and/or π–π Stacking Interactions and the Formation of Various Superstructures

A series of platinum(II) terpyridine complexes with tetraphenylethylene-modified alkynyl ligands has been designed and synthesized. The introduction of the tetraphenylethylene motif has led to aggregation-induced emission (AIE) properties, which upon self-assembly led to the formation of metal-metal-to-ligand charge transfer (MMLCT) behavior stabilized by Pt···Pt and/or π-π interactions. Tuning the steric bulk or hydrophilicity through molecular engineering of the platinum(II) complexes has been found to alter their spectroscopic properties and result in interesting superstructures (including nanorods, nanospheres, nanowires, and nanoleaves) in the self-assembly process. The eye-catching color and emission changes upon varying the solvent compositions may have potential applications in chemosensing materials for the detection of microenvironment changes. Furthermore, the importance of the directional Pt···Pt and/or π-π interactions on the construction of distinctive superstructures has also been examined by UV-vis absorption and emission spectroscopy and transmission electron microscopy. This work represents the interplay of both inter- and intramolecular interactions as well as the energies of the two different chromophoric/luminophoric systems that may open up a new route for the development of platinum(II)-AIE hybrids as functional materials.

Molecular Design of Novel Classes of Luminescent Transition Metal Complexes and Their Use in Sensing, Biolabeling, and Cell Imaging

The design and synthesis of a number of luminescent transition metal complexes will be described, and their rich photophysical properties will be examined. Upon the incorporation of various functionalities to the ancillary ligands, not only will their electronic absorption and emission properties be tuned, but also they may serve as optical and luminescent sensors for ions and molecules of biological interest and as reagents and probes for biolabeling and cell imaging.

Living supramolecular polymerization achieved by collaborative assembly of platinum(II) complexes and block copolymers

Significance Living supramolecular polymerization has emerged as an efficient pathway for the fabrication of supramolecular assemblies with precisely controlled dimensions and diverse architectures. This work achieves living supramolecular polymerization by the collaborative assembly of two structurally dissimilar components, namely, the platinum(II) complexes and the block copolymers. This work largely broadens the scope of supramolecular monomers for living supramolecular polymerization and in the construction of supramolecular-based heterojunctions with large lattice mismatch, which represents a distinct advantage over the existing methods based on single-component systems in devising living supramolecular polymerization. This work may open up new, simple one-pot strategies for the fabrication of segmented supramolecular-based heterojunctions with different optical, charge transport, and catalytic properties for directional excitation energy, and electron and hole transport. An important feature of biological systems to achieve complexity and precision is the involvement of multiple components where each component plays its own role and collaborates with other components. Mimicking this, we report living supramolecular polymerization achieved by collaborative assembly of two structurally dissimilar components, that is, platinum(II) complexes and poly(ethylene glycol)-b-poly(acrylic acid) (PEG-b-PAA). The PAA blocks neutralize the charges of the platinum(II) complexes, with the noncovalent metal–metal and π–π interactions directing the longitudinal growth of the platinum(II) complexes into 1D crystalline nanostructures, and the PEG blocks inhibiting the transverse growth of the platinum(II) complexes and providing the whole system with excellent solubility. The ends of the 1D crystalline nanostructures have been found to be active during the assembly and remain active after the assembly. One-dimensional segmented nanostructures with heterojunctions have been produced by sequential growth of two types of platinum(II) complexes. The PAA blocks act as adapters at the heterojunctions for lattice matching between chemically and crystallographically different platinum(II) complexes, achieving heterojunctions with a lattice mismatch as large as 21%.

Transition Metal-Based Photofunctional Materials: Recent Advances and Potential Applications

This chapter highlights the importance of structure–property relationships in transition metal complexes for the construction of molecular- and supramolecular-based photofunctional materials and summarizes the recent advancements of this class of complexes with potential applications in the areas of energy, catalysis, materials, biology, and diagnostics.

Energy Landscape in Supramolecular Coassembly of Platinum(II) Complexes and Polymers: Morphological Diversity, Transformation, and Dilution Stability of Nanostructures

Establishment of energy landscape has emerged as an efficient pathway for improved understanding and manipulation of both thermodynamic and kinetic behaviors of complicated supramolecular systems. Herein, we report the establishment of energy landscapes of supramolecular coassembly of platinum(II) complexes and polymers, as well as the fabrication of nanostructures with enhanced complexity and intriguing properties from the coassembly systems. In the energy landscape, coassembly at room temperature has been found to only allow the longitudinal growth of platinum(II) complexes and block copolymers into core-shell nanofibers that are the kinetically trapped products. Thermal annealing can switch on the transverse growth of platinum(II) complexes and block copolymers to produce core-shell nanobelts that are the thermodynamically stable nanostructures. The extents of the transverse growth are found to increase with thermal annealing temperatures, leading to nanobelts with larger widths. Besides, rapid quenching of a hot coassembly mixture to room temperature can capture intermediate nanobelt- block-nanofiber nanostructures that are metastable and capable of converting to nanobelts upon further incubation at room temperature. Moreover, sonication treatment has been found to couple with the energy landscape of the coassembly system and open a unique energy-driven pathway to activate the kinetically forbidden nanofiber-to-nanobelt morphological transformation. Furthermore, based on the established energy landscapes, nanosphere- block-nanobelt nanostructures with distinct segmented architectures have been fabricated by thermal annealing of the ternary mixture of platinum(II) complexes, block copolymers, and polymer brushes in a one-pot and single-step procedure. Finally, the nanobelts and nanosphere- block-nanobelt nanostructures are found to possess intriguing morphological stability against acid and dilution, exhibiting characteristics that are important for promising biomedical applications.