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 gabs 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.

Realization of Distinct Mechano- and Piezochromic Behaviors via Alkoxy Chain Length-Modulated Phosphorescent Properties and Multidimensional Self-Assembly Structures of Dinuclear Platinum(II) Complexes.

In this work, through the introduction of different lengths of alkoxy chains to the dinuclear cyclometalated platinum(II) complexes, the apparent color, solubility, luminescence properties, and self-assembly behaviors have been remarkably modulated. In the solid state, the luminescence properties have been found to arise from emission origins that switch between the 3MMLCT excited state in the red solids and the 3IL excited state in the yellow state, depending on the alkoxy chain lengths. The luminescence of the yellow solids is found to show obvious bathochromic shifts under mechanical grinding and decreased intensity under controllable hydrostatic pressure. However, the emission of the red solids exhibits both a bathochromic shift and reduced intensity due to the isotropic compression-induced shortening of the Pt···Pt and π-π distances. By combining the data obtained from X-ray diffraction (XRD), infrared (IR), and X-ray single crystal structure, a better understanding of the relationship between molecular aggregation and photophysical properties has been realized, suggesting that the length of the alkoxy chains plays an important role in governing the supramolecular assemblies.

A platinum(II) molecular hinge with motions visualized by phosphorescence changes.

With the rapidly growing exploration of artificial molecular machines and their applications, there is a strong demand to develop molecular machines that can have their motional states and configuration/conformation changes detectable by more sensitive and innovative methods. A visual artificial molecular hinge with phosphorescence behavior changes is designed and synthesized using square-planar cyclometalated platinum(II) complex and rigid aromatic alkynyl groups as the building blocks to construct the wings/flaps and axis, respectively. The molecular motions of this single molecular hinge and its reversible processes can be powered by both solvent and temperature changes. The rotary motion can be conveniently observed by the visual phosphorescence changes from deep-red to green emission in real time.

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.

Solvent-Induced and Temperature-Promoted Aggregation of Bipyridine Platinum(II) Triangular Metallacycles and Their Near-Infrared Emissive Behaviors.

A series of bipyridine platinum(II) complexes with different sizes of triangular metallacycles and alkyl/oligoether chains has been synthesized and characterized. They are packed in a zig-zag fashion with the formation of dimeric structures according to their X-ray crystal structures. Different emission origins are observed due to the different sizes of the triangular ligands. Their morphologies could be tuned by the modification of the molecular structures with different metallacyclic alkynyl ligands and alkyl/oligoether chains and solvents. More interestingly, unusual electronic absorption changes and upfield shifts of the aromatic proton resonances are observed upon increasing the temperature, suggesting further aggregation of the architectures. Near-infrared (NIR) emission is also realized through the tuning of the π-π stacking, Pt⋅⋅⋅Pt interactions, and the packing of planar metallacycles.

Supramolecular Self-Assembly and Dual-Switch Vapochromic, Vapoluminescent, and Resistive Memory Behaviors of Amphiphilic Platinum(II) Complexes.

A series of amphiphilic platinum(II) complexes with tridentate N-donor ligands has been synthesized and characterized. Different supramolecular architectures are constructed using the amphiphilic molecules as the building blocks through the formation of Pt···Pt and π-π stacking interactions in aqueous media. The aggregation-deaggregation-aggregation self-assembly behavior together with obvious spectroscopic changes could be fine-tuned by the addition of THF in aqueous media. More interestingly, one of the complexes is found to show fast response and high selectivity toward alcohol and water vapors with good reversibility, leading to drastic color and luminescence changes, and hence unique dual switching behavior, with the water molecules readily displaced by the alcohol vapor. Rapid writing and erasure have been realized via the control of a jet or a stream of alcohol vapor flow. In addition, it has been employed as active materials in the fabrication of small-molecule solution-processable resistive memory devices, exhibiting stable and promising binary memory performance with threshold voltages of ca. 3.4 V, high ON/OFF ratios of up to 105 and long retention times of over 104 s. The vapochromic and vapoluminescent materials are demonstrated to have potential applications in chemosensing, logic gates, VOC monitoring, and memory functions.

Unique Spectral Overlap and Resonant Energy Transfer between Europium(II) and Ytterbium(III) Cations: No Quantum Cutting.

Samples of the Ca3 Sc2 Si3 O12 (CSS) host singly doped with Eu2+ or Yb3+ , doubly doped with Eu2+ and Yb3+ , and triply doped with Ce3+ , Eu2+ and Yb3+ were synthesized by a sol-gel combustion process under reducing conditions. Unlike previous reports of Eu2+ →Yb3+ energy transfer in other systems, the energy transfer is resonant in the CSS host and the transfer efficiency reaches 100 % for lightly doped samples. The transfer mechanism is multipolar rather than electron transfer for the sample compositions employed herein. The emission intensity of Yb3+ is further enhanced by co-doping with Ce3+ in addition to Eu2+ . The quantum efficiencies of the doped materials range between 9 % and 93 %.

Cyclometalated Platinum(II) Complexes of 1,3-Bis(1-n-butylpyrazol-3-yl)benzenes: Synthesis, Characterization, Electrochemical, Photophysical, and Gelation Behavior Studies.

A new series of cyclometalated platinum(II) complexes of N^C^N ligands, where N^C^N = 1,3-bis(1-n-alkylpyrazol-3-yl)benzene (bpzb), namely, [Pt(bpzb)Cl] (1 and 2) and [Pt(bpzb)(C≡C-R)] (3-10) (R = C6H5, C6H4-OCH3-p, C6H4-NO2-p, C6H4-NH2-p, 4-cholesteryl phenyl carbamate, and cholesteryl methylcarbamate) were synthesized and characterized. Their electrochemical and photophysical properties were investigated. Two of the platinum(II) complexes were also structurally characterized by X-ray crystallography, and short intermolecular C-H···Pt contacts were observed. Vibronic-structured emission bands originating from triplet IL (3IL) excited states of the bpzb ligands with mixing of some 3MLCT [dπ(Pt)→π*(bpzb)] character were observed in solution state. Interestingly, complex 5 shows a low-energy emission that is derived from the involvement of the p-nitrophenylethynyl ligand. Complex 9 with hydrophobic cholesteryl 4-ethynylphenyl carbamate ligand was found to form stable metallogels in several organic solvents, which are responsive to mechanical sonication and thermal stimuli and show circular dichroism activity.

Rigidifying Effect of Metal-Organic Frameworks: Protect the Conformation, Packing Mode, and Blue Fluorescence of a Soft Piezofluorochromic Compound under Pressures up to 8 MPa.

We demonstrate that the conformation, packing mode, and blue fluorescence of a soft piezofluorochromic compound can be preserved by structurally fixing it into a solid calcium metal-organic framework (Ca-MOF, LIFM-40), which can survive pressures up to 8 MPa. DFT calculations have been combined with experimental results to indicate that the ligands adopting a specific conformation and packing without π···π interactions are the reasons for its rigidified blue emission.