Insulated π-conjugated 2,2'-bipyridine transition-metal complexes: enhanced photoproperties in luminescence and catalysis

2,2'-Bipyridine has been identified as a privileged ligand scaffold for photofunctional transition metal complexes. We herein report on the synthesis and photoproperties of an insulated π-conjugated 2,2'-bipyridine with a linked rotaxane structure consisting of permethylated α-cyclodextrin (PM α-CD) and oligo(p-phenylene ethynylene). The insulated π-conjugated 2,2'-bipyridine exhibited enhanced ligand performance in the solid-state emitting biscyclometalated Ir complexes and visible-light-driven Ni catalysts owing to π-extension and remote steric effects based on the linked rotaxane structure.

Linker-dependent control of the chiroptical properties of polymethylene-vaulted trans-bis[(β-iminomethyl)naphthoxy]platinum(II) complexes

The effects of polymethylene bridges on the chiroptical properties of trans-bis[(β-iminomethyl)naphthoxy]platinum(II) platforms were examined both experimentally and theoretically using newly designed planar chiral Pt analogues (1) having three-dimensional superstructures. A series of optically pure polymethylene-vaulted Pt complexes (R)- and (S)-1 were synthesized and characterized with regard to the chiroptical behaviour of the trans-bis[(β-iminomethyl)naphthoxy]platinum(II) platforms. These complexes were found to exhibit structure-dependent chiroptical characteristics in solution, such that the absolute values of specific rotation, the circular dichroism dissymmetry factor (gabs) and the circularly polarized luminescence dissymmetry factor (glum) all increased upon shortening the polymethylene bridges. Density functional theory and time dependent density functional theory calculations were used to analyse vaulted and non-vaulted complexes, which demonstrated that the present linker-dependent chiroptical properties resulted from constraint-induced changes in the square planar Pt coordination centres rather than from chiral distortion along the coordination platforms.

Supramolecular Strategy to Achieve Distinct Optical Characteristics and Boosted Chiroptical Enhancement Based on the Closed Conformation of Platinum(II) Complexes

Synthesis of chiral molecules for understanding and revealing the expression, transfer, and amplification of chirality is beneficial to explore effective chiral medicines and high-performance chiroptical materials. Herein, we report a series of square-planar phosphorescent platinum(II) complexes adopting a dominantly closed conformation that exhibit efficient chiroptical transfer and enhancement due to the nonclassical intramolecular C-H···O or C-H···F hydrogen bonds between bipyridyl chelating and alkynyl auxiliary ligands as well as the intermolecular π-π stacking and metal-metal interactions. The spectroscopic and theoretical calculation results demonstrate that the chirality and optic properties are regulated from the molecular level to hierarchical assemblies. Notably, a 154 times larger g_abs value of the circular dichroism signals is obtained. This study provides a feasible design principle to achieve large chiropticity and control the expression and transfer of the chirality.

Vortex Flow-controlled Circularly Polarized Luminescence of Achiral Pt(II) Complex Aggregates Assembled at the Air-Water Interface

Circularly polarized luminescence (CPL) has been researched for various applications by control of characteristics such as chirality and magnitude. Supramolecular chirality has been prepared by vortex motion as a mechanical stimulus; however, CPL has yet to be controlled precisely and reproducibly. In this work, the first precise control of CPL under vortex flow conditions at an air-water interface is reported. The supramolecular chirality of aggregates consisting of an achiral trans-bis(salicylaldiminato)Pt(II) complex bearing hexadecyl chains is induced and controlled with vortex flow at the air-water interface, whereas the complex naturally forms an achiral amorphous solid with non-chiroptical properties under non-vortex conditions. The CPL direction and magnitude (g_lum value) of the Pt(II) complex aggregates can be adjusted precisely according to the vortex conditions, including the rotatory direction and flow rate. Vortex-flow-induced emission enhancement is also observed upon an increase in the rate of the vortex flow.

High-Rate Organic Cathode Constructed by Iron-Hexaazatrinaphthalene Tricarboxylic Acid Coordination Polymer for Li-Ion Batteries

The sluggish ion-transport in electrodes and low utilization of active materials are critical limitations of organic cathodes, which lead to the slow reaction dynamics and low specific capacity. In this study, the hierarchical tube is constructed by iron-hexaazatrinaphthalene tricarboxylic acid coordination polymer (Fe-HATNTA), using HATNTA as the self-engaged template to coordinate with Fe²⁺ ions. This Fe-HATNTA tube with hierarchical porous structure ensures the sufficient contact between electrolyte and active materials, shortens the diffusion distance, and provides more favorable transport pathways for ions. When employed as the cathode for rechargeable Li-ion batteries, Fe-HATNTA delivers a high specific capacity (244 mAh g^-1 at 50 mA g^-1 , 91% of theoretical capacity), excellent rate capability (128 mAh g^-1 at 9 A g^-1 ), and a long-term cycle life (73.9% retention over 3000 cycles at 5 A g^-1 ). Moreover, the Li⁺ ions storage and conduction mechanisms are further disclosed by the ex situ and in situ characterizations, kinetic analyses, and theoretical calculations. This work is expected to boost further enthusiasm for developing the hierarchical structured metal-organic coordination polymers with superb ionic storage and transport as high-performance organic cathodes.

In Situ Assembly of Platinum(II)-Metallopeptide Nanostructures Disrupts Energy Homeostasis and Cellular Metabolism

Nanostructure-based functions are omnipresent in nature and essential for the diversity of life. Unlike small molecules, which are often inhibitors of enzymes or biomimetics with established methods of elucidation, we show that functions of nanoscale structures in cells are complex and can implicate system-level effects such as the regulation of energy and redox homeostasis. Herein, we design a platinum(II)-containing tripeptide that assembles into intracellular fibrillar nanostructures upon molecular rearrangement in the presence of endogenous H₂O₂. The formed nanostructures blocked metabolic functions, including aerobic glycolysis and oxidative phosphorylation, thereby shutting down ATP production. As a consequence, ATP-dependent actin formation and glucose metabolite-dependent histone deacetylase activity are downregulated. We demonstrate that assembly-driven nanomaterials offer a rich avenue to achieve broad-spectrum bioactivities that could provide new opportunities in drug discovery.

Enhancement of Chiroptical Responses of trans-Bis[(β-iminomethyl)naphthoxy]platinum(II) Complexes with Distorted Square Planar Coordination Geometry

The relationship between the coordination geometry and photophysical properties of trans‐bis[(β‐iminomethyl)naphthoxy]platinum(II) was investigated both experimentally and theoretically. A series of platinum(II) complexes with differently substituted iminomethyl groups were synthesized, and their photophysical properties were examined in solution, in the crystalline, and in the PMMA film‐dispersed state, respectively (PMMA=poly(methyl methacrylate)). These complexes showed structure‐dependent emission spectra, in which the color of the luminescence in the crystalline state varied over a range of about 40 nm depending on the specific bowl‐shaped molecular structure. The chiral complexes with (R,R)‐ and (S,S)‐configurations were found to have structure‐dependent chiroptical properties both in solution and the PMMA film‐dispersed state such that the intensity of circular dichroism (CD) and circularly polarized luminescence (CPL) were enhanced with bulky cyclic substituents at the nitrogen atoms. A theoretical study using density functional theory (DFT) and time‐dependent (TD)‐DFT calculations revealed that the enhancement of chiroptical responses is due to the amplification of the magnetic dipole moment caused by the distortion of the square planar geometry.

Square planar Au(III), Pt(II) and Cu(II) complexes with quinoline-substituted 2,2':6',2″-terpyridine ligands: From in vitro to in vivo biological properties

Cancer is the second leading cause of death worldwide. Cisplatin has challenged cancer treatment; however, resistance and side effects hamper its use. New agents displaying improved activity and more reduced side effects relative to cisplatin are needed. In this work we present the synthesis, characterization and biological activities of three complexes with quinoline-substituted 2,2':6',2″-terpyridine ligand: [Pt(4'-(2-quin)-terpy)Cl](SO₃CF₃) (1), [Au(4'-(2-quin)-terpy)Cl](PF₆)₂·CH₃CN (2) and [Cu(4'-(2-quin)-terpy)Cl](PF₆) (3). The three complexes displayed a high antiproliferative activity in ovarian carcinoma cell line (A2780) and even more noticeable in a colorectal carcinoma cell line (HCT116) following the order 3 > 2 > 1. The complexes IC₅₀ are at least 20 × lower than the IC₅₀ displayed by cisplatin (15.4 μM) in HCT116 cell line while displaying at the same time, much reduced cytotoxicity in a normal dermal fibroblast culture. These cytotoxic activities seem to be correlated with the inclination angles of 2-quin unit to the central pyridine. Interestingly, all complexes can interact with calf-thymus DNA (CT-DNA) in vitro via different mechanisms, although intercalation seems to be the preferred mechanism at least for 2 and 3 at higher concentrations of DNA. Moreover, circular dichroism (CD) data seems to indicate that complex 3, more planar, induces a high destabilization of the DNA double helix (shift from B-form to Z-form). Higher the deviation from planar, the lower the cytotoxicity displayed by the complexes. Cellular uptake may be also responsible for the different cytotoxicity exhibited by complexes with 3 > 2 >1. Complex 2 seems to enter cells more passively while complex 1 and 3 might enter cells via energy-dependent and -independent mechanisms. Complexes 1-3 were shown to induce ROS are associated with the increased apoptosis and autophagy. Moreover, all complexes dissipate the mitochondrial membrane potential leading to an increased BAX/BCL-2 ratio that triggered apoptosis. Complexes 2 and 3 were also shown to exhibit an anti-angiogenic effect by significantly reduce the number of newly formed blood vessel in a CAM model with no toxicity in this in vivo model. Our results seem to suggest that the increased cytotoxicity of complex 3 in HCT116 cells and its potential interest for further translation to pre-clinical mice xenografts might be associated with: 1) higher % of internalization of HCT116 cells via energy-dependent and -independent mechanisms; 2) ability to intercalate DNA and due to its planarity induced higher destabilization of DNA; 3) induce intracellular ROS that trigger apoptosis and autophagy; 4) low toxicity in an in vivo model of CAM; 5) potential anti-angiogenic effect.

Circularly polarized luminescence of nanoassemblies via multi-dimensional chiral architecture control

Circularly polarized luminescence (CPL) materials are currently an important class of chiroptical materials that are attracting increasing interest. Nanoassemblies constructed from chiral or achiral building blocks show great potential for achieving CPL-active nanomaterials with high quantum yields and dissymmetry factors, which is crucial for further applications. In nanoassemblies, the dimensional morphology affects the chiroptical properties significantly since the microscopic packing modes will affect the luminescence processes and chirality transfer processes. In this review, we will show some examples for illustrating the relationship between multi-dimensional morphology and chiroptical properties. Furthermore, with dimensional morphology tuning, higher dissymmetry factors would be obtained. We hope to provide a useful and powerful insight into the design and control of CPL-active nanoassemblies via morphology control.

Beyond Chiral Organic (p-Block) Chromophores for Circularly Polarized Luminescence: The Success of d-Block and f-Block Chiral Complexes

Chiral molecules are essential for the development of advanced technological applications in spintronic and photonic. The best systems should produce large circularly polarized luminescence (CPL) as estimated by their dissymmetry factor (g _lum), which can reach the maximum values of -2 ≤ g _lum ≤ 2 when either pure right- or left-handed polarized light is emitted after standard excitation. For matching this requirement, theoretical considerations indicate that optical transitions with large magnetic and weak electric transition dipole moments represent the holy grail of CPL. Because of their detrimental strong and allowed electric dipole transitions, popular chiral emissive organic molecules display generally moderate dissymmetry factors (10^-5 ≤ g _lum ≤ 10^-3). However, recent efforts in this field show that g _lum can be significantly enhanced when the chiral organic activators are part of chiral supramolecular assemblies or of liquid crystalline materials. At the other extreme, chiral Eu^III- and Sm^III-based complexes, which possess intra-shell parity-forbidden electric but allowed magnetic dipole transitions, have yielded the largest dissymmetry factor reported so far with g _lum ~ 1.38. Consequently, 4f-based metal complexes with strong CPL are currently the best candidates for potential technological applications. They however suffer from the need for highly pure samples and from considerable production costs. In this context, chiral earth-abundant and cheap d-block metal complexes benefit from a renewed interest according that their CPL signal can be optimized despite the larger covalency displayed by d-block cations compared with 4f-block analogs. This essay thus aims at providing a minimum overview of the theoretical aspects rationalizing circularly polarized luminescence and their exploitation for the design of chiral emissive metal complexes with strong CPL. Beyond the corroboration that f-f transitions are ideal candidates for generating large dissymmetry factors, a special attention is focused on the recent attempts to use chiral Cr^III-based complexes that reach values of g _lum up to 0.2. This could pave the way for replacing high-cost rare earths with cheap transition metals for CPL applications.

Rational Design of Axially Chiral Platinabinaphthalenes with Aggregation-Induced Emission for Red Circularly Polarized Phosphorescent Organic Light-Emitting Diodes

Circularly polarized luminescent (CPL) materials have received a lot of interest due to their potential applications in next-generation displays. However, the development of easily accessible red circularly polarized phosphorescent emitters for practical organic light-emitting diodes fabrication remains a grand challenge. In this paper, we report a new family of CPL-active platinum complexes based on the binaphthalene chiral platform. These axially chiral platinabinaphthalenes were facile synthesized by directly incorporating platinum(II) into the π-conjugated backbone of a commercially available enantiopure binaphthalene derivate. These complexes exhibit aggregation-induced circularly polarized phosphorescence enhancement with high quantum yields of up to 66% and luminescence dissymmetry factors of around 2.6 × 10^-3. Moreover, solution-processable circularly polarized organic light-emitting diodes (CPOLEDs) using these complexes as emitters show good performance with the maximum luminance of up to 3500 cd m^-2 and dissymmetry factor values of around 1.0 × 10^-3. These findings by the rational design of axially chiral platinabinaphthalenes are important for the development of high-performance CPL complexes for CPOLEDs.

Aggregation and Tunable Color Emission Behaviors of l-Glutamine-Derived Platinum(II) Bipyridine Complexes by Hydrogen-Bonding, π-π Stacking and Metal-Metal Interactions

An l-glutamine-derived functional group was introduced to the bis(arylalkynyl)platinum(II) bipyridine complexes 1-4. The emission could be switched between the ³ MLCT excited state and the triplet excimeric state through solvent or temperature changes, which is attributed to the formation and disruption of hydrogen-bonding, π-π stacking, and metal-metal interactions. Different architectures with various morphologies, such as honeycomb nanostructures and nanospheres, were formed upon solvent variations, and these changes were accompanied by ¹ H NMR and distinct emission changes. Additionally, yellow and red emissive metallogels were formed at room temperature due to the different aggregation behaviors introduced by the substituent groups on bipyridine. The thermoresponsive metallogel showed emission behavior with tunable colors by controlling the temperature. The negative Gibbs free-energy change (ΔG) and the large association constant for excimer formation have suggested that the molecules undergo aggregation through hydrogen-bonding, π-π, and metal-metal interactions, resulting in triplet excimeric emission.

Platinum(II) complexes of pyridine–amine ligands with phenol substituents: isotactic supramolecular polymers

The platinum(II) complexes [PtCl(SMe2)(κ2-N,N′-L)]Cl and [PtMe(SMe2)(κ2-N,N′-L)]Cl, L = 2-C5H4NCH2NH-x-C6H4OH (x = 2, 3, or 4), have been prepared and structurally characterized. In all cases, the complexes form supramolecular polymers in the solid state by NH··Cl and OH··Cl hydrogen bonding to the chloride anion. The ligands are chiral at the amine nitrogen atom, and in all cases, the polymers are isotactic, formed by self-recognition or narcissistic self-assembly. The structures in the crystalline state all have the Me2S ligand trans to pyridyl, but in solution, the methylplatinum(II) complexes isomerise slowly to give an equilibrium with the isomers having the methyl group trans to the pyridyl donor.

Amplified circularly polarized phosphorescence from co-assemblies of platinum(ii) complexes

Molecules capable of producing zero-field circularly polarized phosphorescence (CPP) are highly valuable for chiroptoelectronic applications that rely on triplet exciton. However, the paucity of tractable molecular design rules for obtaining CPP emission has inhibited full utilization. We report amplification of CPP by the formation of helical co-assemblies consisting of achiral square planar cycloplatinated complexes and small fractions of homochiral cycloplatinated complexes. The latter has a unique Pfeiffer effect during the formation of superhelical co-assemblies, enabling versatile chiroptical control. Large dissymmetry factors in electronic absorption (g _abs, 0.020) and phosphorescence emission (g _lum, 0.064) are observed from the co-assemblies. These values are two orders of magnitude improved relative to those of individual molecules. In addition, photoluminescence quantum yields (PLQY) also increase by a factor of ten. Our structural, photophysical, and quantum chemical investigations reveal that the chiroptical amplification is attributable to utilization of both the magnetically allowed electronic transition and asymmetric coupling of excitons. The strategy overcomes the trade-off between g _lum and PLQY which has frequently been found for previous molecular emitters of circularly polarized luminescence. It is anticipated that our study will provide new insight into the future research for the exploitation of the full potential of CPP.

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.

Pt⋯Pt interaction triggered tuning of circularly polarized luminescence activity in chiral dinuclear platinum(ii) complexes

Two couples of chiral binuclear Pt(ii) complexes are capable of displaying distinct CPL activities in the green to red region through tuning Pt⋯Pt interactions.

Coordination preference of hexa(2-pyridyl)benzene with copper(ii) directed by hydrogen bonding

Coordination modes of hexa(2-pyridyl)benzene ligand with copper(ii) ions were controlled by different solvents mainly due to hydrogen bonding.