Two rhenium compounds with benzimidazole ligands: synthesis and DNA interactions

Two rhenium compounds: cis-tetrachlorotetrabenzimidazoldirhenium(iii) chloride - I and tetrabenzimidazoldioxorhenium(v) - II have been synthesized and characterized. X-ray data are presented for the new complex II. I and II show strong emission that has been used to investigate their interaction with several non-canonical DNA structures. Both compounds have a quenching effect on the fluorescence intensity upon addition of the investigated oligonucleotides; I was more selective for binding G4-than II. Association constant values obtained for I and II with G-quadruplexes reached 106 M-1, which suggests a strong interaction between both complexes and these sequences. FRET-melting assays show that I and II have a rather high level of stabilization of ckit1 and ckit2 quadruplexes. I is toxic against macrophages RAW267.7 only in high concentrations, while complex II shows no toxicity against these cells. I and II accumulate inside cells in different degrees. Molecular dynamic simulation studies have provided insights into the binding modes of II with ckit1 and ckit2 G-quadruplexes. The results obtained show the DNA binding activity of the rhenium complexes and their ability to be players in the anti-cancer fight since they can bind to non-canonical DNA forms in oncogene promoters, accumulate in some cancer cells, and influence the cancer cells microenvironment.

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.

A Luminescence Assay in the Red for the Detection of Hydrogen Peroxide and Glucose Based on Metal Coordination Polyelectrolyte-Induced Supramolecular Self-Assembly of Alkynylplatinum(II) Complexes

A new sensing strategy towards hydrogen peroxide based on metal coordination polyelectrolyte-driven self-assembly of alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) complex was demonstrated. The cationic in situ-generated Ag(I)-thiocholine coordination polyelectrolytes were shown to induce the supramolecular self-assembly of anionic low-energy red-emissive alkynylplatinum(II) bzimpy complexes via non-covalent Pt(II)⋅⋅⋅Pt(II), electrostatic and π-π stacking interactions. The presence of hydrogen peroxide was shown to inhibit the formation of coordination polyelectrolytes and the coordination polyelectrolyte-induced self-assembly of platinum(II) complexes. The weakening of Pt(II)⋅⋅⋅Pt(II), electrostatic and π-π stacking interactions was supported by UV-vis absorption, emission, and resonance light scattering (RLS) studies. The present assay was also applied to probe glucose indirectly based on the enzymatic reaction of glucose oxidase on the substrate. Operating in a label-free manner, together with the low-energy red emission and large Stokes shift of alkynylplatinum(II) complexes, these features render the proposed design attractive for biological applications.

Induced Self-Assembly and Disassembly of Alkynylplatinum(II) 2,6-Bis(benzimidazol-2'-yl)pyridine Complexes with Charge Reversal Properties: "Proof-of-Principle" Demonstration of Ratiometric Förster Resonance Energy Transfer Sensing of pH

A series of pH-responsive alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) complexes with charge-reversal properties was synthesized, and the supramolecular assemblies between conjugated polyelectrolyte, PFP-OSO₃^-, and [Pt{bzimpy(TEG)₂}{C≡C-C₆H₃-(COOH)₂-3,5}]Cl (1) have been studied using UV-vis absorption, emission, and resonance light scattering (RLS) spectroscopy. An efficient Förster resonance energy transfer (FRET) from PFP-OSO₃^- donor to the aggregated 1 as acceptor with the aid of Pt(II)···Pt(II) interactions has been presented, which leads to a growth of triplet metal-metal-to-ligand charge transfer (³MMLCT) emission in the low-energy red region. The two-component PFP-OSO₃^--1 ensemble was then exploited as a "proof-of-principle" concept strategy for pH sensing by tracking the ratiometric emission changes. With the aid of judicious molecular design on the pH-driven charge-reversal property, the polyelectrolyte-induced self-assembly and the FRET from PFP-OSO₃^- to the platinum(II) aggregates have been modulated. Together with its excellent reversibility and photostability, the extra stability provided by the Pt(II)···Pt(II) and π-π stacking interactions on top of the electrostatic and hydrophobic interactions existing in polyelectrolye-complex assemblies has led to a selective and sensitive pH sensing assay.

Synthesis of platinum(II)-complex end-tethered polymers: spectroscopic properties and nanostructured particles

Although metal-containing polymers have been widely studied as a novel class of functional soft materials, the microphase separation between polymeric segments and metal-ligand complexes has been less addressed, which is critical to control their structures and functions. To do this, short-chain polystyrenes (PSs) have been end-functionalized with nanosized square-planar platinum(II) complexes. The platinum(II)-comprising polymers were found to show significant luminescence enhancement in chloroform/methanol solvent mixtures upon increasing the methanol composition. By modulating both the PS length and solvent quality, various self-assembled morphologies formed controllably in the mixed solvents and typical examples include nanofibers, nanoellipsoids, and nanospheres. More interestingly, the inside structures of these polymer particles are shown to be lamellar with sub-10 nm spacings, wherein the PS blocks are alternatively aligned with the platinum(II) units. Such a luminescence enhancement and hierarchical nanostructured particles originate from a subtle combination of directional Pt(II)⋯Pt(II) and/or π-π stacking interactions between the platinum(II) units and the solvophobic effect between the PS blocks. This work suggests that by microphase separating polymer chains with nanosized metal-ligand complexes, metal-containing polymers can self-assemble to form sub-10 nm scale nanostructures showcasing desired properties and functions.

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.

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.

Molecular Alignment of Alkynylplatinum(II) 2,6-Bis(benzimidazol-2-yl)pyridine Double Complex Salts and the Formation of Well-Ordered Nanostructures Directed by Pt···Pt and Donor-Acceptor Interactions

A new class of alkynylplatinum(II) bzimpy (bzimpy = bis(benzimidazol-2-yl)pyridine) double complex salts (DCSs) containing dialkoxynaphthalene or pyromellitic diimide moieties on the alkynyl ligand has been reported to display distinct morphological properties compared to their precursor alkynylplatinum(II) complexes, with the capability of being aligned by the directional Pt···Pt and/or π-π stacking interactions. The incorporation of donor and acceptor units on the alkynyl ligands has been found to significantly perturb the alignment of the oppositely charged complex ions in the DCSs to stack in a twisted head-to-head manner, attributed to the additional driving forces of electrostatic and donor-acceptor interactions. The modulation of the Pt···Pt distances and the extent of aggregate formation have been demonstrated by altering the charge matching between the platinum(II) bzimpy moieties and the donor or acceptor moieties on the alkynyl ligand.

Photo-modulated supramolecular self-assembly of ortho-nitrobenzyl ester-based alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine complexes

The enhanced supramolecular self-assembly behaviors of photo-caged platinum(II) complexes have been triggered by applying light as the external stimulus. Distinct morphological transformation of the nanoaggregates has been observed in the photo-caged complexes before and after UV irradiation.

Ru(II)-Based Metallo-Supramolecular Polymer with Tetrakis(N-methylbenzimidazolyl)bipyridine for a Durable, Nonvolatile, and Electrochromic Device Driven at 0.6 V

Low-voltage operation, high durability, and long memory time are demanded for electrochromic (EC) display device applications. Metallo-supramolecular polymers (MSPs), composed of a metal ion and ditopic ligand, are one of the recently developed EC materials, and the ligand modification is expected to tune the redox potential of MSP. In order to lower the redox potential of MSP, tetrakis(N-methylbenzimidazolyl)bipyridine (L_Bip) was designed as an electronically rich ligand. Ru-based MSP (polyRu-L_Bip) was successfully synthesized by 1:1 complexation of RuCl₂(DMSO)₄ with L_Bip. The molecular weight (M_w) was high (8.8 × 10⁶ Da) enough to provide a simple ¹H NMR spectrum, of which the proton peaks could be assigned by the comparison with the spectrum of the corresponding mono-Ru complex. The redox potential (E_1/2) between Ru(II/III) was 0.51 V versus Ag/Ag⁺, which was much lower than the redox potential of previously reported Ru-based MSP with bis(terpyridyl)benzene (0.95 V vs Ag/Ag⁺). The polymer film exhibited reversible, distinct color changes between violet and light green-yellow upon applying very low potentials of 0 and 0.6 V vs Ag/Ag⁺, respectively. The appearance and disappearance of the metal-to-ligand charge transfer absorption by the electrochemical redox between Ru(II/III) were confirmed using in situ spectro-electrochemical measurement. A solid-state EC device with polyRu-L_Bip was revealed to have large optical contrast (ΔT 54%), fast response time (1.37 s for bleaching and 0.67 s for coloration), remarkable coloration efficiency (571 cm²/C), and high durability for the repeated color changes more than 20,000 cycles. The device also showed a long optical memory time of up to 19 h to maintain 40% to the initial contrast under the open circuit conditions. It is considered that the stabilization of the Ru(III) state by L_Bip suppressed the self-coloring to Ru(II) inside the device.

Aggregation and Supramolecular Self-Assembly of Low-Energy Red Luminescent Alkynylplatinum(II) Complexes for RNA Detection, Nucleolus Imaging, and RNA Synthesis Inhibitor Screening

As an important nuclear substructure, the nucleolus has received increasing attention because of its significant functions in the transcription and processing of ribosomal RNA in eukaryotic cells. In this work, we introduce a proof-of-concept luminescence assay to detect RNA and to accomplish nucleolus imaging with the use of the supramolecular self-assembly of platinum(II) complexes. Noncovalent interactions between platinum(II) complexes and RNA can be induced by the introduction of a guanidinium group into the complexes, and accordingly, a high RNA affinity can be achieved. Interestingly, the aggregation affinities of platinum(II) complexes enable them to display remarkable luminescence turn-on upon RNA binding, which is a result of the strengthening of noncovalent Pt(II)···Pt(II) and π-π stacking interactions. The complexes exhibit not only intriguing spectroscopic changes and luminescence enhancement after RNA binding but also specific nucleolus imaging in cells. As compared to fluorescent dyes, the low-energy red luminescence and large Stokes shifts of platinum(II) complexes afford a high signal-to-background autofluorescence ratio in nucleolus imaging. Additional properties, including long phosphorescence lifetimes and low cytotoxicity, have endowed the platinum(II) complexes with the potential for biological applications. Also, platinum(II) complexes have been adopted to monitor the dynamics of the nucleolus induced by the addition of RNA synthesis inhibitors. This capability allows the screening of inhibitors and can be advantageous for the development of antineoplastic agents. This work provides a novel strategy for exploring the application of platinum(II) complex-based cell imaging agents based on the mechanism of supramolecular self-assembly. It is envisaged that platinum(II) complexes can be utilized as valuable probes because of the aforementioned appealing advantages.

Functional Platinum(II) Complexes with Four-Photon Absorption Activity, Lysosome Specificity, and Precise Cancer Therapy

Multiphoton materials are in special demand in the field of photodynamic therapy and multiphoton fluorescence imaging. However, rational design methodology for these brands of materials is still nascent. This is despite transition-metal complexes favoring optimized nonlinear-optical (NLO) activity and heavy-atom-effected phosphorescent emission. Here, three four-photon absorption (4PA) platinum(II) complexes (Pt1-Pt3) are achieved by the incorporation of varied functionalized C^N^C ligands with high yields. Pt1-Pt3 exhibit triplet metal-to-ligand charge-transfer transitions at ∼460 nm, which are verified multiple times by transient absorption spectra, time-dependent density functional theory calculations, and low-temperature emission spectra. Further, Pt1-Pt3 undergo 4PA. Notably, one of the complexes, Pt2, has maximum 4PA cross-sectional values of up to 15.2 × 10^-82 cm⁸ s³ photon^-3 under excitation of a 1600 nm femtosecond laser (near-IR II window). The 4PA cross sections vary when Pt2 is binding to lecithin and when it displays its lysosome-specific targeting behavior. On the basis of the excellent 4PA property of Pt2, we believe that those 4PA platinum(II) complexes have great potential applications in cancer theranostics.

Synthesis and hierarchical self-assembly of luminescent platinum(ii)-containing telechelic metallopolymers

Luminescent telechelic metallopolymers functionalized with platinum(ii) complexes can self-assemble into flowerlike micelles, and the resulting flowers can further form vesicle-like architectures in solution.

Luminescent Pt(2,6-bis(N-methylbenzimidazol-2-yl)pyridine)X+: a comparison with the spectroscopic and electrochemical properties of Pt(tpy)X+ (X = Cl, CCPh, Ph, or CH3)

A series of platinum(ii) pincer complexes of the formula Pt(mbzimpy)X+, 1(a-d), (mbzimpy = 2,6-bis(N-methylbenzimidazol-2-yl)pyridine; X = Cl; (a), CCPh; (b), Ph; (c), or CH3; (d), CCPh = phenylacetylide, and Ph = Phenyl) have been synthesized and characterized. Electronic absorption and emission, as well as electrochemical properties of these compounds, have been investigated. Pt(tpy)X+ analogs (tpy = 2,2';6'2''-terpyridine), 2(a-d), have also been investigated and compared. Electrochemistry shows that 1 and 2 analogs undergo two chemically reversible one-electron reduction processes that are shifted cathodically along the a < b < c < d series. Notably, these reductions occur at slightly higher negative potentials in the case of 1. The absorption spectra of 1 and 2 in acetonitrile exhibit ligand-centered (1LC) transitions (ε ≈ 104 M-1 cm-1) in the UV region and metal-to-ligand-charge transfer (1MLCT) transitions (ε ≈ 103 M-1 cm-1) in the visible region. The corresponding visible bands of 1b and 2b have been assigned to 1(LLCT/MLCT) mixed state (LLCT: ligand-to-ligand-charge transfer). The preceding 1LC and 1MLCT transitions of 1 occur at lower energies than that of 2. These 1LC transitions have distinctly been blue-shifted along a < c < d in 2, but occur at nearly identical energies in 1. Conversely, 1MLCT transitions are red-shifted along a < c < d in both the analogs. The 77 K glassy solutions of 1 and 2 exhibit an intense vibronically-structured emission band at λmax(0-0) in the 470-560 nm range. This band is red-shifted along b < a ≤ c < d in 1 and along a ≤ d ≈ c ≪ b in 2. The main character of these emissions is assigned to 3LLCT emissive state in 1b and 2b, whereas to 3LC in the rest of the compounds. Relative stabilization of these spin-forbidden emissive states is discussed by invoking configuration mixing with the higher-lying 3MLCT state.

Platinum(ii) non-covalent crosslinkers for supramolecular DNA hydrogels

Manipulation of non-covalent metal–metal interactions allows the fabrication of functional metallosupramolecular structures with diverse supramolecular behaviors. The majority of reported studies are mostly designed and governed by thermodynamics, with very few examples of metallosupramolecular systems exhibiting intriguing kinetics. Here we report a serendipitous finding of platinum(ii) complexes serving as non-covalent crosslinkers for the fabrication of supramolecular DNA hydrogels. Upon mixing the alkynylplatinum(ii) terpyridine complex with double-stranded DNA in aqueous solution, the platinum(ii) complex molecules are found to first stack into columnar phases by metal–metal and π–π interactions, and then the columnar phases that carry multiple positive charges crosslink the negatively charged DNA strands to form supramolecular hydrogels with luminescence properties and excellent processability. Subsequent platinum(ii) intercalation into DNA competes with the metal–metal and π–π interactions at the crosslinking points, switching on the spontaneous gel-to-sol transition. In the case of a chloro (2,6-bis(benzimidazol-2′-yl)pyridine)platinum(ii) complex, with [Pt(bzimpy)Cl]⁺ serving as a non-covalent crosslinker where the metal–metal and π–π interactions outcompete platinum(ii) intercalation, the intercalation-driven gel-to-sol transition pathway is blocked since the gel state is energetically more favorable than the sol state. Interestingly, the ligand exchange reaction of the chloro ligand in [Pt(bzimpy)Cl]⁺ with glutathione (GSH) has endowed the complexes with enhanced hydrophilicity, decreasing the planarity of the complexes, and turning off the metal–metal and π–π interactions at the crosslinking points, leading to GSH-triggered hydrogel dissociation.

We report a serendipitous finding of platinum(ii) complexes serving as non-covalent crosslinkers for the fabrication of supramolecular DNA hydrogels.

Solution aggregation of platinum(ii) triimine methyl complexes

Self-assembly processes are investigated in two model compounds, Pt(L)(CH₃)⁺ (where, L = 2,6-bis(N-methylbenzimidazol-2-yl)pyridine OR 2,2′;6′2′′-terpyridine), employing NMR. Structural conformations of formed assemblies are confirmed by 2D NOESY.

Amyloid Protein-Induced Supramolecular Self-Assembly of Water-Soluble Platinum(II) Complexes: A Luminescence Assay for Amyloid Fibrillation Detection and Inhibitor Screening

Amyloid fibrillation has been acknowledged as a hallmark of a number of neurodegenerative ailments such as Alzheimer's disease. Accordingly, efficient detection of amyloid fibrillation will allow for great advances in the field of biomedical applications as well as in achieving early medical diagnosis. In this work, a luminescence assay for the sensitive and specific detection of amyloid fibrillation was developed by using platinum(II) complexes as sensing platforms. Supramolecular self-assembly of platinum(II) complexes was induced upon addition of amyloid, leading to alterations in the spectroscopic and luminescence properties of the complexes. As compared to fluorescent dyes, luminescent platinum(II) complexes exhibit attractive large Stokes shifts, phosphorescence lifetimes in the microsecond to submicrosecond regime, and low-energy red emission after aggregation, which are advantageous to biological imaging. At the same time, the platinum(II) complex adopted herein was found to have high photostability, high selectivity and specificity, and low cytotoxicity. The proposed design is the very first approach to detect amyloid fibrillation through the supramolecular self-assembly of luminescent platinum(II) complexes.

Protamine-Induced Supramolecular Self-Assembly of Red-Emissive Alkynylplatinum(II) 2,6-Bis(benzimidazol-2'-yl)pyridine Complex for Selective Label-Free Sensing of Heparin and Real-Time Monitoring of Trypsin Activity

A label-free detection assay is developed based on the design and synthesis of a new anionic alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine complex with water-soluble pendants. With the aid of electrostatic interaction and noncovalent metal-metal and π-π stacking interactions, protamine is shown to induce supramolecular self-assembly of platinum(II) complexes with drastic UV-vis absorption and red emission changes. On the basis of the strong binding affinity of protamine and heparin, the ensemble has been further employed to probe heparin by monitoring the spectroscopic changes. Other than heparin, this ensemble can also detect the activity of trypsin, which can hydrolyze protamine into fragments, leading to the deaggregation of platinum(II) complexes. By modulation of the self-assembly properties of platinum(II) complexes via real-time UV-vis absorption and emission studies, the reported assay has been demonstrated to be a sensitive and selective detection method for trypsin, as well as trypsin inhibitor screening, which is essential for drug discovery.

Photoresponsiveness of Anthracene-Based Supramolecular Polymers Regulated via a σ-Platinated 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene Photosensitizer

Anthracene and its derivatives have attracted tremendous interest in recent years because of their intriguing photoresponsive behaviors. Our research group has previously constructed anthracene-based supramolecular polymers, which display multicycle anthracene-endoperoxide photoswitching in a macroscopic manner. However, high-energy light excitation (λ = 365-460 nm) is required for anthracene-to-endoperoxide photooxygenation, giving rise to severe photodegradation problems. In this work, we have developed an effective approach to addressing this issue, by encapsulating a σ-platinated 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) photosensitizer into anthracene-based supramolecular polymeric systems. The platination effect enhances π-electron delocalization, while promoting intersystem crossing from singlet to triplet excited states. Accordingly, the σ-platinated BODIPY photosensitizer displays excellent ¹O₂ production capability, facilitating anthracene-to-endoperoxide transformation under low-energy irradiation conditions (λ = 520-590 nm). This leads to the breakup of supramolecular polymers and gels, which can be restored at room and elevated temperatures because of the reversible endoperoxide-to-anthracene deoxygenation process. Overall, the rational design of a σ-metalated photosensitizer opens up a new avenue to regulating the photoresponsiveness of supramolecular polymers under mild and nondestructive conditions.

Sub-10 nm Scale Lamellar Structures with a High Degree of Long-Range Order Fabricated by Orthogonal Self-Assembly of Crown Ether/Secondary Dialkylammonium Recognition and Metal···Metal/π-π Interactions

We here present an orthogonal self-assembly strategy to fabricate a series of metallosupramolecular polymers by coupling planar platinum(II) complexes and starlike poly(ε-caprolactone), through Pt···Pt/π-π interactions and host-guest recognition between secondary dialkylammonium salts and crown ether groups. The solid metallosupramolecular polymers exhibit sub-10 nm scale lamellar structures and one of them occupies an extraordinary degree of long-range order. The platinum(II) complexes can be regarded as an individual supramolecular block to microphase segregate the polymeric segment. Moreover, the metallosupramolecular polymers show intense luminescence and appreciable proton conductivity, originating from these two supramolecular connection modes, respectively. This work paves the way for fabricating metallosupramolecular polymers showing both highly ordered nanostructures and multifunctional properties.

A Luminescence Turn-On Assay for Acetylcholinesterase Activity and Inhibitor Screening Based on Supramolecular Self-Assembly of Alkynylplatinum(II) Complexes on Coordination Polymer

A new approach toward acetylcholinesterase (AChE) detection has been demonstrated based on the electrostatic interactions between anionic alkynylplatinum(II) complex molecules and cationic coordination polymer, together with the spectroscopic and emission characteristics of alkynylplatinum(II) complexes upon supramolecular self-assembly. This process involves strengthening of distinct noncovalent Pt(II)···Pt(II) and π-π stacking interactions, which is evidenced by UV-vis absorption, emission, and resonance light scattering results. Such a method has been applied to AChE inhibitor screening, which is important as the demand for AChE inhibitor assays arises along with the drug development for Alzheimer's disease. It affords an emission turn-on response and operates in a continuous and label-free fashion. The low-energy red emission and large Stokes shift of alkynylplatinum(II) complexes are advantageous to biological applications.

Onge PBJ, Binder JF, Suter R, Burford N, Macdonald CLB. 2,6-Bis(benzimidazol-2-yl)pyridine complexes of group 14 elements

Variants of the 2,6-bis(benzimidazol-2-yl)pyridine ligand are used to synthesize novel group 14 complexes of germanium and tin. The salts are characterized by X-ray crystallography, NMR, UV-vis, and the Lewis acidity of some examples are probed.

A halogen ion-selective phosphorescence turn-on probe based on induction of Pt–Pt interactions

A halogen ion induced self-assembly of square-planar platinum complexes has been, for the first time, observed and applied as a turn-on phosphorescent probe for Cl⁻.

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.

Synthesis of bimetallic complexes bridged by 2,6-bis(benzimidazol-2-yl) pyridine derivatives and their catalytic properties in transfer hydrogenation

A series of binuclear rhodium(i) and iridium(i) complexes with 2,6-bis(benzimidazol-2-yl) pyridine (bzimpy) derivatives were synthesized and characterized by elemental analysis and spectroscopic methods. The molecular and crystal structures of complex 3d were determined by the single crystal X-ray diffraction technique. Their monometallic analogues were prepared to compare the catalytic properties of the bimetallic complexes. To determine the catalyst properties that result in a cooperative, bimetallic enhancement of the reaction rate, the systematic variation of the intermetallic distance and the ligand donor properties of the bimetallic complexes were explored based on the transfer hydrogenation reactions of ketones.

Supramolecular Assembly of Phosphole Oxide Based Alkynylplatinum(II) 2,6-Bis(N-alkylbenzimidazol-2'-yl)pyridine Complexes-An Interplay of Hydrophobicity and Aromatic π-Surfaces

A new class of phosphole oxide based alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine (bzimpy) complexes were synthesized and characterized. Their self-assembly was driven by hydrophobic-hydrophobic and π-π stacking interactions. The self-assembly properties were also investigated by UV/Vis absorption spectroscopy, which revealed that the alkyl-chain length of the bzimpy moiety and the π-surface area of the alkynyl ligand have significant influence on the overall self-assembly process. The alkyl-chain length also affected the morphological structures of the aggregates, which were studied by transmission electron microscopy and scanning electron microscopy.

Arginine-Rich Peptide-Induced Supramolecular Self-Assembly of Water-Soluble Anionic Alkynylplatinum(II) Complexes: A Continuous and Label-Free Luminescence Assay for Trypsin and Inhibitor Screening

A water-soluble anionic alkynylplatinum(II) 2,6-bis(benzimidazol-2'-yl)pyridine (bzimpy) complex has been strategically designed and synthesized to show supramolecular self-assembly with cationic arginine-rich peptides through unique noncovalent Pt(II)···Pt(II) and π-π stacking interactions. Upon introduction of trypsin, the arginine-rich peptides can be hydrolyzed into small fragments and deaggregation of the platinum(II) complex molecules is observed. The aggregation-deaggregation process has been probed by UV-vis absorption, emission, and resonance light scattering (RLS) studies. This platinum(II) complex has been employed for developing a new, continuous and label-free luminescence assay for trypsin as well as for inhibitor screening, and has been successfully applied to detect trypsin in diluted serum solutions.

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

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%.

The phosphorescence properties of a series of diarylethene-containing platinum complexes: the effect of ligand photoisomerization

Benefitting from isomerization in the ancillary-ligand diarylethene, a control of phosphorescence efficiency becomes available.

Platinum and Gold Complexes for OLEDs

Encouraging efforts on the design of high-performance organic materials and smart architecture during the past two decades have made organic light-emitting device (OLED) technology an important competitor for the existing liquid crystal displays. Particularly, the development of phosphorescent materials based on transition metals plays a crucial role for this success. Apart from the extensively studied iridium(III) complexes with d(6) electronic configuration and octahedral geometry, the coordination-unsaturated nature of d(8) transition metal complexes with square-planar structures has been found to provide intriguing spectroscopic and luminescence properties. This article briefly summarizes the development of d(8) platinum(II) and gold(III) complexes and their application studies in the fabrication of phosphorescent OLEDs. An in-depth understanding of the nature of the excited states has offered a great opportunity to fine-tune the emission colors covering the entire visible spectrum as well as to improve their photophysical properties. With good device engineering, high performance vacuum-deposited OLEDs with external quantum efficiencies (EQEs) of up to 30 % and solution-processable OLEDs with EQEs of up to 10 % have been realized by modifying the cyclometalated or pincer ligands of these metal complexes. These impressive demonstrations reveal that d(8) metal complexes are promising candidates as phosphorescent materials for OLED applications in displays as well as in solid-state lighting in the future.