Supramolecular assembly of platinum-containing polyhedral oligomeric silsesquioxanes: an interplay of intermolecular interactions and a correlation between structural modifications and morphological transformations

Supramolecular assembly of amphiphilic platinum(ii) Schiff base complexes: diverse spectroscopic changes and nanostructures through rational molecular design and solvent control

A new class of amphiphilic tetradentate platinum(ii) Schiff base complexes has been designed and synthesized. The self-assembly properties by exploiting the potential Pt⋯Pt interactions of amphiphilic platinum(ii) Schiff base complexes in the solution state have been systematically investigated. The presence of Pt⋯Pt interactions has further been supported by computational studies and non-covalent interaction (NCI) analysis of the dimer of the complex. The extent of the non-covalent Pt⋯Pt and π-π interactions could be regulated by a variation of the solvent compositions and the hydrophobicity of the complexes, which is accompanied by attractive spectroscopic and luminescence changes and leads to diverse morphological transformations. The present work represents a rare example of demonstration of directed cooperative assembly of amphiphilic platinum(ii) Schiff base complexes by intermolecular Pt⋯Pt interactions in solution with an in-depth mechanistic investigation, providing guiding principles for the construction of supramolecular structures with desirable properties using platinum(ii) Schiff base building blocks.

Impact of Ring-Closing on the Photophysical Properties of One-Dimensional π-Conjugated Molecular Aggregate

The self-assembled state of molecules plays a pivotal role in determining how inherent molecular properties transform and give rise to supramolecular functionalities and has long attracted attention. However, understanding the influence of morphologies spanning the nano- to mesoscopic scales of supramolecular assemblies derived from identical intermolecular interactions has been notoriously challenging due to dynamic structural change and monomer exchange of assemblies in solution. In this study, we demonstrate that curved one-dimensional molecular assemblies (supramolecular polymers) of lengths of around 70-200 nm, originating from the same luminescent molecule, exhibit distinct photoluminescent properties when they form closed circular structures (toroids) versus when they possess chain termini in solution (random coils). By exploiting the difference in kinetic stability between the toroids and random coils, we developed a dialysis protocol to selectively purify the former. It was revealed that these terminus-free closed structures manifest higher energy and more efficient luminescence compared with their mixed state with random coils. Time-resolved fluorescence measurements unveiled that random coils, due to their dynamic structural fluctuation in solution, generate local defects throughout the main chain, leading to luminescence from lower energy levels. In mixtures of the two assemblies, luminescence was exclusively observed from such a lower energy level of random coils, a result attributed to energy transfer between the assemblies. This work emphasizes that for identical supramolecular assemblies, only averaged properties have traditionally been considered, but their structures at the nano- to mesoscopic scale are important especially if they have a certain degree of shape persistency even in solution.

Platinum(II) terpyridine-based supramolecular polymer gels with induced chirality

Metal-ligand binding plays a crucial role in regulating the photophysical properties of supramolecular gels. In this study, we designed 1-Pt complexes comprising a central benzene-1,3,5-tricarboxamide unit functionalized with three terpyridines, which can form supramolecular gels with Pt(II). The resulting supramolecular gel of 1-Pt exhibited strong orange emission, which was attributed to the metal-to-metal ligand charge transfer during gel formation. Furthermore, the temperature-dependent absorption spectrum changes of the supramolecular polymer 1-Pt exhibited a nonsigmoidal transition, following a cooperative pathway involving a nucleation-elongation mechanism. Additionally, the strategy for the co-assembling system involving 1-Pt with chiral molecules (D-form and L-form) induced the helical arrangement of 1-Ptvia chiral additives in supramolecular metallogels.

Lamellar assembly and nanostructures of amphiphilic boron(iii) diketonates through suitable non-covalent interactions

Cooperative assemblies of amphiphilic boron(iii) diketonate compounds, which are found to be driven by the formation of non-covalent π–π and hydrophobic interactions in THF–water solution, result in the construction of nanosheet of lamellar packing.

Phosphorescent Host-Guest Complexes on the Basis of Polyhedral Oligomeric Silsesquioxane-Functionalized Metallotweezers

Phosphorescent host-guest systems have attracted considerable attention because of their intriguing properties and diverse applications. In this study, a polyhedral oligomeric silsesquioxane-functionalized gold(III) tweezer receptor has been designed and synthesized. It is capable of sandwiching platinum(II) terpyridine compounds into its cavity with a high noncovalent binding affinity (association constants: ∼10⁵ M^-1 in chloroform). The resulting heterometallic host-guest complexes exhibit enhanced phosphorescent emission compared with those of the individual species in chloroform, thanks to the prevention of vibration and rotation upon noncovalent complexation. They can further assemble into nanospheres in chloroform/diethyl ether (1:9, v/v) owing to phase segregation between the metallotweezer/guest motif and the peripheral polyhedral oligomeric silsesquioxane unit. When terpyridine platinum(II) chloride serves as the complementary guest, the resulting noncovalent system displays an intraligand emission at the individual host-guest complexed state yet excimeric emission at the supramolecular assembled state, yielding the phosphorescent solvatochromic behaviors. Overall, the polyhedral oligomeric silsesquioxane-functionalized metallotweezer combines guest encapsulation and supramolecular assembly capabilities, which provides new avenues for color-tunable phosphorescent materials.

Elucidation of the key role of Pt···Pt interactions in the directional self-assembly of platinum(II) complexes

Molecular self-assembly provides a bottom-up platform to design supramolecular functional materials, attracting numerous interests in material sciences. The utilization of platinum(II) complexes as building blocks of supramolecular assemblies opens up the unique noncovalent Pt···Pt interaction as one of the driving forces, imparting the supramolecular materials with rich spectroscopic features. However, the exact role of Pt···Pt interactions in molecular assembly remains elusive. The current study combines experimental and computational techniques to elucidate the role of Pt···Pt interactions in the self-assembly process of a representative amphiphilic platinum(II) complex. This work demonstrates the directional role of Pt···Pt interactions in assisting the molecular assembly in an anisotropic manner, achieving the formation of ordered self-assembled structures.

Here, we report the use of an amphiphilic Pt(II) complex, K[Pt{(O₃SCH₂CH₂CH₂)₂bzimpy}Cl] (PtB), as a model to elucidate the key role of Pt···Pt interactions in directing self-assembly by combining temperature-dependent ultraviolet-visible (UV-Vis) spectroscopy, stopped-flow kinetic experiments, quantum mechanics (QM) calculations, and molecular dynamics (MD) simulations. Interestingly, we found that the self-assembly mechanism of PtB in aqueous solution follows a nucleation-free isodesmic model, as revealed by the temperature-dependent UV-Vis experiments. In contrast, a cooperative growth is found for the self-assembly of PtB in acetone–water (7:1, vol/vol) solution, which is further verified by the stopped-flow experiments, which clearly indicates the existence of a nucleation phase in the acetone–water (7:1, vol/vol) solution. To reveal the underlying reasons and driving forces for these self-assembly processes, we performed QM calculations and show that the Pt···Pt interactions arising from the interaction between the p_z and d_z² orbitals play a crucial role in determining the formation of ordered self-assembled structures. In subsequent oligomer MD simulations, we demonstrate that this directional Pt···Pt interaction can indeed facilitate the formation of linear structures packed in a helix-like fashion. Our results suggest that the self-assembly of PtB in acetone–water (7:1, vol/vol) solution is predominantly driven by the directional noncovalent Pt···Pt interaction, leading to the cooperative growth and the formation of fibrous nanostructures. On the contrary, the self-assembly in aqueous solution forms spherical nanostructures of PtB, which is primarily due to the predominant contribution from the less directional hydrophobic interactions over the directional Pt···Pt and π−π interactions that result in an isodesmic growth.

Double-Decker Silsesquioxanes Self-Assembled in One-Dimensional Coordination Polymeric Nanofibers with Emission Properties

The urgent needs for photoactive materials in industry drive fast evolution of synthetic procedures in many branches of chemistry, including the chemistry of silsesquioxanes. Here, we disclose an effective protocol for the synthesis of novel double-decker silsesquioxanes decorated with two (styrylethynylphenyl)terpyridine moieties (DDSQ_Ta-b). The synthesis strategy involves a series of silylative and Sonogashira coupling reactions and is reported for the first time. DDSQ_Ta-b were employed as nanocage ligands to promote self-assembly in the presence of transition metals (TM), i.e., Zn2+, Fe2+, and Eu3+ ions, to form one-dimensional (1D) coordination polymeric nanofibers. Additionally, ultraviolet-promoted and reversible E-Z isomerization of the C═C bond within the ligand structures may be exploited to tune their emission properties. These findings render such complexes promising candidates for applications in materials chemistry. This is the first example of 1D coordination polymers bearing DDSQ-based nodes with TM ions.

Phosphorescent Soft Salt Based on Platinum(II) Complexes: Photophysics, Self-Assembly, Thermochromism, and Anti-counterfeiting Application

A new platinum(II) complex-based soft salt S1, ([Pt(tpp)(ed)]⁺[Pt(pba) (CN)₂]^-) (tpp = 2-(4-(trifluoromethyl)phenyl)pyridine, ed = ethane-1,2-diamine, pba = 4-(2-pyridyl)benzaldehyde), was designed and synthesized. UV-visible absorption and photoluminescence (PL) spectra were studied to elucidate the nature of ground and excited states. The soft salt complex was found to show self-assembly properties with the assistance of electrostatic, π-π stacking, and Pt···Pt interactions, resulting in the remarkable emergence of low-energy absorption and PL bands. Morphological transformation of S1 from undefined nanosized aggregates to nanofibers with different solvent compositions has been demonstrated. Interestingly, a luminescent polymer film was prepared by doping S1 into a polyethylene glycol matrix. The film displayed distinctive emission color change from yellow to red upon heating. Eventually, a high-level anti-counterfeiting application was accomplished using a time-resolved imaging technique based on the thermochromic luminescence property and long emission decay time displayed by S1. It is anticipated that this work can provide deep insights into the control of intermolecular interactions between cationic and anionic complexes of soft salt upon exposure to different external stimuli, resulting in the development of smart luminescent materials for various applications.

Luminescent cyclometalated platinum(ii) complexes with acyclic diaminocarbene ligands: structural, photophysical and biological properties

Four new cyclometalated Pt(ii) complexes bearing acyclic diaminocarbene (ADC) ligands, [Pt(C^N)Cl{C(NHXyl)(NHR)}] [C^N = 2,6-difluorophenylpyridine (dfppy), phenylquinoline (pq); R = Pr 3a, 4a, CH₂Ph 3b, 4b], were prepared by the nucleophilic attack on the isocyanide [Pt(C^N)Cl(CNXyl)] (C^N = dfppy 1, pq 2) by the corresponding amine RNH₂ (R = Pr, CH₂Ph). Complexes 3 show in their ¹H NMR spectra in CDCl₃ a notable concentration dependence, with a clear variation of the δ_H (NHXyl) signal, suggesting an assembling process implying donor-acceptor NH_XylCl bonding, also supported by 1D-PGSE (Pulse Field Gradient Spin Echo) and 2D-DOSY (Diffusion Ordered Spectroscopy) NMR experiments in solution and X-ray diffraction studies. The intermolecular interactions in compounds 3a and 3b were studied by using Hirshfeld surface analysis and Non-Covalent Interaction (NCI) methods on their X-ray structures. Their photophysical properties were investigated by absorption and emission spectroscopies and also by TD-DFT calculations performed on 3a and 4b. These complexes show green (3) or orange (4) phosphorescence, attributed to a mixed ³IL/³MLCT excited state. The carbene ligand does not affect the emission maxima but it produces an increase of the quantum yields in relation to the isocyanide in the precursors. In fluid solutions, the emission is not concentration-dependent, but the complexes may show aggregation induced emission as detailed for complexes 3a and 4a. In addition, cytotoxicity studies in the human cell lines A549 (lung carcinoma) and HeLa (cervix carcinoma) showed good activity for these complexes and 3a, 3b and 4a exhibit a strong effect on DNA electrophoretic mobility. To the best of our knowledge, compounds 3 and 4 represent the first examples of cycloplatinated complexes bearing acyclic diamino carbenes with antiproliferative properties.

Thermally Stable Fluorogenic Zn(II) Sensor Based on a Bis(benzimidazole)pyridine-Linked Phenyl-Silsesquioxane Polymer

A 2,6-bis(2-benzimidazolyl) pyridine-linked silsesquioxane-based semi-branched polymer was synthesized, and its photophysical and metal-sensing properties have been investigated. The polymer is thermally stable up to 285 °C and emits blue in both solid and solution state. The emission of the polymer is sensitive to pH and is gradually decreased and quenched upon protonation of the linkers. The initial emission color is recoverable upon deprotonation with triethylamine. The polymer also shows unique spectroscopic properties in both absorption and emission upon long-term UV irradiation, with red-shifted absorption and emission not present in a simple blended system of phenylsilsesquioxane and linker, suggesting that a long-lived energy transfer or charge separated state is present. In addition, the polymer acts as a fluorescence shift sensor for Zn(II) ions, with red shifts observed from 464 to 528 nm, and reversible binding by the introduction of a competitive ligand such as tetrahydrofuran. The ion sensing mechanism can differentiate Zn(II) from Cd(II) by fluorescence color shifts, which is unique because they are in the same group of the periodic table and possess similar chemical properties. Finally, the polymer system embedded in a paper strip acts as a fluorescent chemosensor for Zn(II) ions in solution, showing its potential as a solid phase ion extractor.

Soft salts based on platinum(II) complexes with high emission quantum efficiencies in the near infrared region for in vivo imaging

Two soft salts (S1 and S2) based on platinum(ii) complexes with a near-infrared emission have been designed and synthesized. It has been demonstrated that S2 has a high photostability and a low cytotoxicity, and it has been successfully applied to in vivo imaging for the first time.

Multinuclear PtII Complexes: Why Three is Better Than Two to Enhance Photophysical Properties

The self-assembly of platinum complexes is a well-documented process that leads to interesting changes of the photophysical and electrochemical behavior as well as to a change in reactivity of the complexes. However, it is still not clear how many metal units must interact in order to achieve the desired properties of a large assembly. This work aimed to clarify the role of the number of interacting PtII units leading to an enhancement of the spectroscopic properties and how to address inter- versus intramolecular processes. Therefore, a series of neutral multinuclear PtII complexes were synthesized and characterized, and their photophysical properties at different concentration were studied. Going from the monomer to dimers, the growth of a new emission band and the enhancement of the emission properties were observed. Upon increasing the platinum units up to three, the monomeric blue emission could not be detected anymore and a concentration independent bright-yellow/orange emission, due to the establishment of intramolecular metallophilic interactions, was observed.

Synthesis of metallo-supramolecular materials based on terpyridine functionalized double-decker silsesquioxane with improved complexation efficiency

Silsesquioxane-based transition-metal complexes have come to the forefront due to the ability of silsesquioxane to control nanostructures and properties. However, some difficulties in complete complexation and purification limit the widespread use of transition-metal-based supramolecular coordination complexes comprising silsesquioxane. Herein, 2 different approaches have been proposed for the synthesis of metallo-supramolecular materials on the basis of ruthenium(II)-terpyridine functional double-layer silsesquioxane (DDSQ) (Tpy/Ru-DDSQ) (Routes 1 and 2). In Route 1, complexation was followed by functionalization of DDSQ with the ligand, whereas in Route 2, complexation was performed before the ligand was inserted into the DDSQ. Tpy/Ru-DDSQ obtained from both approaches was characterized by 1H NMR, X-ray photoelectron spectrometer, and FTIR and found in the same structure. Both methods were fully discussed and their merits were explored. The complexation yield of the routes was similar. However, the results based on NMR and UV-Vis spectroscopy demonstrated that the incorporation rate of DDSQ into the complex was quite high in Route 2. As far as is known, this is the first study based on the effects of complexing Tpy ligands before/after binding to the target compound, particularly to silsesquioxane-based materials.

Platinum(II) Probes for Sensing Polyelectrolyte Lengths and Architectures

Platinum(II) polypyridine complexes of a square-planar geometry have been used as spectroscopic reporters for quantification of various charged species through non-covalent metal-metal interactions. The characterization of molecular weights and architectures of polyelectrolytes represents a challenging task in polymer science. Here, we report the utilization of platinum(II) complex probes and non-covalent metal-metal interactions for sensing polyelectrolyte lengths and architectures. It is found that the platinum(II) probes can bind to linear polyelectrolytes via electrostatic attractions and give rise to significant spectroscopic changes associated with the formation of metal-metal interactions, and the extent of the spectroscopic changes is found to increase with the lengths of the linear polyelectrolytes. Besides, the platinum(II) probes have been found to co-assemble with the linear polyelectrolytes to form well-defined nanofibers, and the lengths of the linear polyelectrolytes can be directly estimated from the diameter of the nanofibers under transmission electron microscopy observation. Interestingly, upon mixing with the platinum(II) probes, polyelectrolytes with bottlebrush architectures have been found to exhibit larger spectroscopic changes than linear polyelectrolytes with the same chemical composition. Combined with the reported theoretical studies on counterion condensation of polyelectrolytes, the platinum(II) complexes are found to function as spectroscopic probes for sensing the charge densities of the polyelectrolytes with different lengths and diverse architectures. Moreover, platinum(II) probes pre-organized in nanostructured aggregates have been found to intercalate into double-stranded DNA, which are naturally occurring biological polyelectrolytes with helical architectures and intercalation sites, to give significant enhancement of spectroscopic changes when compared to the intercalation of monomeric platinum(II) probes into double-stranded DNA.

Photochromic Barbiturate Pendant-Containing Benzo[b]phosphole Oxides with Co-Assembly Property and Photoinduced Morphological Changes

A series of novel barbiturate pendant-containing benzo[b]phosphole oxides has been demonstrated to exhibit photochromic and co-assembly properties. Both the open form and the photogenerated closed form of the diarylethene-based benzo[b]phosphole oxides have displayed color changes with new appearance of the bathochromic-shifted lowest-energy absorption bands upon addition of the H-bonding ditopic receptor that is complementary to the barbiturate groups, probably resulting in the formation of a supramolecular polymer. The co-assembly mixtures have displayed dissociation and association processes upon heating and cooling, respectively. Moreover, both the unassembled and co-assembled states of the benzo[b]phosphole oxide have exhibited photoinduced coloration, leading to a near-infrared absorption behavior. Multiaddressable states of the co-assembly mixture with multiple colors have been achieved via the combination of photochromism and thermochromism. More interestingly, photoinduced morphological changes from extensive porous network structures to ring-like aggregates have been observed for the co-assembly upon photoirradiation. The present work provides important insight for further developments of the multiaddressable systems and the supramolecular polymers with photo- and thermo-responsive behaviors, paving the way for the future design of photochromic materials with interesting photocontrollable functions.

Chemically Synthesized Carbon Nanorods with Dual Polarized Emission

We realized the synthesis of carbon nanorods-monodisperse colloidal particles with a length of 50 nm and a width of 20 nm-which can be considered an addition to the family of light-emitting carbon-based nanostructures. Their anisotropic shape is determined by the use of the surfactant aminopropylisobutyl polyhedral oligomeric silsesquioxane, and their optical properties originate from domains of polycyclic aromatic hydrocarbons incorporated within an inorganic framework. The nanorods show dual polarized emission with a quantum yield of 15-20% and emission anisotropy of ∼0.3, which changes from blue (460 nm) to yellow (565 nm) depending on the excitation wavelength. These carbon nanorods expand the range of light-emitting carbon nanomaterials available for optoelectronic and biolabeling applications.

Competitive self-assembly driven as a route to control the morphology of poly(tannic acid) assemblies

With an attempt to develop some supermolecular assemblies of a particular structure through a controllable method, the present study developed two distinct assembly patterns for Poly(Tannic Acid) (PTA) by means of adjusting the components and composition of a binary solvent system. The assembly mechanism was explored through the comparison of theoretical calculations and experimental results with respect to how solvent sets affect the nature of intermolecular interactions among oligomers. The results indicate that the morphology of the aggregates of PTA is determined from the nature of the intermolecular interactions among oligomers. While a cuboid shaped aggregate is likely the result of π-π stacking self-assembly, a sphere shaped morphology is formed through intermolecular hydrogen bonding among the oligomers. The results of the present work provide valuable resources to tune the aggregation morphology by quantitatively adjusting the physical properties of the binary solvent.

Telechelic amphiphilic metallopolymers end-functionalized with platinum(ii) complexes: synthesis, luminescence enhancement, and their self-assembly into flowerlike vesicles and giant flowerlike vesicles

Telechelic amphiphilic metallopolymers can self-assemble in solution to create nanosized flowerlike vesicles, where the two platinum(ii) complex ends are connected to the same vesicular core and the central PEG chains form loops as a corona.

Self-assembly of platinum(ii) 6-phenyl-2,2'-bipyridine complexes with solvato- and iono-chromic phenomena

Mono- and di-nuclear organoplatinum(ii) monomers with cyclometalated 6-phenyl-2,2'-bipyridine ligands have been successfully constructed. These systems are capable of displaying intriguing solvato- and iono-chromic phenomena by elaborately manipulating non-covalent PtPt metal-metal and π-π stacking interactions for their self-assembly processes.

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.

Directional Self-Sorting with Cucurbit[8]uril Controlled by Allosteric π-π and Metal-Metal Interactions

To maximize Coulombic interactions, cucurbit[8]uril (CB[8]) typically forms ternary complexes that distribute the positive charges of the pair of guests (if any) over both carbonylated portals of the macrocycle. We present here the first exception to this recognition pattern. Platinum(II) acetylides flanked by 4'-substituted terpyridyl ligands (tpy) form 2:1 complexes with CB[8] in an exclusively stacked head-to-head orientation in a water/acetonitrile mixture. The host encapsulates the pair of tpy substituents, and both positive Pt centers sit on top of each other at the same CB[8] rim, leaving the other rim free of any interaction with the guests. This dramatic charge imbalance between the CB[8] rims would be electrostatically penalizing, were it not for allosteric π-π interactions between the stacked tpy ligands, and possible metal-metal interactions between both Pt centers. When both tpy and acetylides are substituted with aryl units, the metal-ligand complexes form 2:2 assemblies with CB[8] in aqueous medium, and the directionality of the assembly (head-to-head or head-to-tail) can be controlled, both kinetically and thermodynamically.

Liquid worm-like and proto-micelles: water solubilization in amphiphile–oil solutions

Weak noncovalent interactions control water dispersion and solubility in oil.

Enhancement of metal–metal interactions inside a large-cavity synthetic host in water

A new host–guest strategy is developed to enhance metal–metal interactions between metal–terpyridyl complexes in aqueous solution.

Synthesis, characterization, and properties of novel UV-resistant poly(urethane-imide)/POSS nanocomposite

In this study, a series of hybrid nanocomposites composed of poly(urethane-imide) (PUI), fluoroethylene vinyl ether copolymers, and octa-aminophenyl polyhedral oligomeric silsesquioxane (POSS) were successfully prepared. Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), contact angle analysis, thermogravimetric analysis (TGA), and dynamic mechanical analysis were used to characterize the hybrid nanocomposites, which were found to have excellent thermostability, mechanical strength, and ultraviolet (UV) resistance. The SEM results showed that POSS nanoparticles, at low content level, could disperse homogeneously in the PUI matrix. The TGA results confirmed that the thermostability of the hybrid nanocomposites was significantly improved by the addition of POSS. Moreover, the UV-resistant property of the nanocomposites was evaluated based on the change in mechanical property and weight loss caused by the UV radiation. POSS (5 wt%) achieved the highest efficiency in enhancing the UV resistance of the nanocomposites. After UV radiation, the tensile modulus of the nanocomposite without POSS decreased to 187 MPa, and the mass loss was 7.26%. In contrast, the tensile modulus of the nanocomposite containing 5 wt% POSS increased from 412 MPa to 444 MPa, and the mass loss was only 3.76%.

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.

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

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-PEG₁₆, 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-PEG₁₆ 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-PEG₁₆ 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-PEG₁₂ exhibited dynamic behavior that led to broadening of the length distribution within 48 h. After aging for 4 weeks in solution, Pt-PEG₁₂ fibers partially evolved into 2D platelets. Furthermore, self-assembly of Pt-PEG₇ yielded only transient fibers which rapidly evolved into 2D platelets. On addition of further fiber-forming Pt complex (Pt-PEG₁₆), 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.

Facile Synthesis and Self-Assembly of Amphiphilic Polyether-Octafunctionalized Polyhedral Oligomeric Silsesquioxane via Thiol-Ene Click Reaction

We demonstrated here a facile and efficient synthesis of polyhedral oligomeric silsesquioxane-based amphiphilic polymer by thiol-ene click chemistry. The properties of polyhedral oligomeric silsesquioxane (POSS)⁻PEG amphiphilic polymers were studied in detail by a combination of ¹H NMR, 13C NMR, 29Si NMR FT-IR, GPC, and TG analysis. The newly-designed thiol-ene protocol obtains only anti-Markovnikov addition POSS-based amphiphilic polymers when compared with platinum-catalysed hydrosilylation method. The critical micelle concentration (CMC) of the resulting polymers are in the range of 0.011 to 0.050 mg/mL, and dynamic light scattering (DLS) results revealed that the obtained amphiphilic polymers can self-assemble into nanoparticles in aqueous solutions with a bimodal (two peaks) distribution. Furthermore, the specific polymer showed obvious thermo-sensitive behaviour at 45.5 °C.

Selective vesicle aggregation achieved via the self-assembly of terpyridine-based building blocks

Herein, we report the self-assembly of a mono terpyridine-based building block modified with long alkyl chains, which gives rise to vesicular aggregates in aqueous media. The vesicles are responsive to transition metal ions, and form different kinds of aggregates after metal-ligand coordination. In particular, Ni(ii) shows a unique influence on morphological transitions, whereby vesicles aggregate and fuse upon the addition of Ni(ii) ions. Spectroscopic and morphological studies are highlighted in this work. Furthermore, the formed vesicles could behave as a matrix for encapsulating fluorescent dyes with similar molecular structure via co-assembly, enabling more accurate observation of vesicle aggregation via confocal laser scanning techniques.