Solvent-Dependent Supramolecular Host-Guest Assemblies of Platinum(II) Tweezers and a Guest System: From Discrete Molecules to High-Ordered Oligomers.

A series of platinum(II) calix[4]arene-based molecular tweezers was synthesized. The studies of the host-guest association with a charge-neutral cyclometalated platinum(II) complex showed a drastic color change and the turning on of near-infrared emission resulting from Pt⋅⋅⋅Pt and π-π interactions. Control of the host-guest assembly process by varying the solvent composition can lead to a change from discrete host and guest molecules to high-ordered host-guest oligomers with the formation of sheet-like nanostructures, demonstrating a rare example of three-state supramolecular host-guest system with high solubility in solvents of diverse polarity. The change in host-guest assembly behaviors could be probed by drastic color changes from yellow to orange to green. The present study provides insights into the systematic design of solvent-responsive molecular materials using molecular tweezers-directed host-guest assembly, with potential applications in colorimetric sensing of changes in the micro-environment.

AuI ⋠⋠⋠AuI Interaction Assisted Host-Guest Interactions and Stimuli-Responsive Self-Assembly in Tetranuclear Alkynylgold(I) Calix[4]arene-Based Isocyanide Complexes.

Multi-stimuli-responsive tetranuclear gold(I) complexes were prepared based on a tetra(alkynyl)calix[4]arene framework, with incorporation of a series of isocyanide ligands of tunable hydrophilicity. This class of complex was found to exhibit high sensitivity towards group IIIA metal ions especially In3+ . Drastic electronic absorption and emission changes were observed, which could be attributed to the formation of AuI ⋅⋅⋅AuI interactions during the binding event. Solvent-induced self-aggregation was also observed upon changing the solvent environment to a more polar medium, with the formation of nanoaggregates and the turning-on of the aurophilic interactions, leading to interesting luminescence and morphological changes. The aggregation process was monitored by UV/Vis absorption, emission and 1 H NMR spectroscopy and dynamic light scattering (DLS) studies, and the morphological changes were studied by electron microscopy. This new class of complex has shown high sensitivity towards external stimuli and demonstrated the feasibility of employing the on-off switching of aurophilicity as an effective design strategy for the construction of functional supramolecular systems.

Luminescence color switching of supramolecular assemblies of discrete molecular decanuclear gold(I) sulfido complexes.

A series of discrete decanuclear gold(I) µ(3)-sulfido complexes with alkyl chains of various lengths on the aminodiphosphine ligands, [Au(10){Ph(2)PN(C(n)H2(n+1))PPh(2)}(4)(µ(3)-S)(4)](ClO(4))(2), has been synthesized and characterized. These complexes have been shown to form supramolecular nanoaggregate assemblies upon solvent modulation. The photoluminescence (PL) colors of the nanoaggregates can be switched from green to yellow to red by varying the solvent systems from which they are formed. The PL color variation was investigated and correlated with the nanostructured morphological transformation from the spherical shape to the cube as observed by transmission electron microscopy and scanning electron microscopy. Such variations in PL colors have not been observed in their analogous complexes with short alkyl chains, suggesting that the long alkyl chains would play a key role in governing the supramolecular nanoaggregate assembly and the emission properties of the decanuclear gold(I) sulfido complexes. The long hydrophobic alkyl chains are believed to induce the formation of supramolecular nanoaggregate assemblies with different morphologies and packing densities under different solvent systems, leading to a change in the extent of Au(I)-Au(I) interactions, rigidity, and emission properties.

Synthesis and Photophysical Studies of Calixarene-Based Alkynylplatinum(II) Terpyridine Complexes with Various Receptor Sites for Colorimetric and Luminescence Sensing of Anions.

A series of mononuclear and dinuclear platinum(II) terpyridine complexes with amide-, sulfonamide-, and urea-containing ligands (1-9) has been successfully designed and synthesized, and their photophysical and anion-binding properties have been studied. The anion-binding properties of the complexes were studied by electronic absorption, emission, and (1)H NMR spectroscopy. Upon the binding with anions, the dinuclear complexes 1-3 exhibit large electronic absorption and emission spectral changes, while for the mononuclear analogues 4-6 much smaller spectral changes were observed. Interesting colorimetric responses towards different anions were observed in dinuclear complexes 1-3. Dinuclear complexes 7-9 are found to be insensitive to anion-binding, which could be attributed to the presence of intramolecular Pt⋅⋅⋅Pt interactions and/or π-π stacking in the complexes that led to the reduced anion-binding affinity.

Addition reaction-induced cluster-to-cluster transformation: controlled self-assembly of luminescent polynuclear gold(I) µ3-sulfido clusters.

Unprecedented addition reaction-induced gold(I) cluster-to-cluster transformation has been observed in the present work. Reaction of the chlorogold(I) precursor, [vdpp(AuCl)2] (vdpp = vinylidenebis(diphenylphosphine)) containing the diphosphine with unsaturated C═C bond, with H2S resulted in a series of polynuclear gold(I) µ3-sulfido clusters bearing Au(I)···Au(I) interactions; the identities of which have been fully characterized by NMR, electrospray-ionization mass spectrometry, elemental analysis, and single crystal X-ray diffraction analysis. Diverse research methods, including UV-vis absorption, (1)H NMR, and (31)P NMR spectroscopy, were employed to detect and monitor the transformation and assembly processes. Supported by single crystal structures, the existence of Au(I)···Au(I) bonding interactions sustains the diverse array of sophisticated polynuclear cluster structures and endues them with rich luminescence features.

From {Au(I)···Au(I)}-coupled cages to the cage-built 2-D {Au(I)···Au(I)} arrays: Au(I)···Au(I) bonding interaction driven self-assembly and their Ag(I) sensing and photo-switchable behavior.

Metal-metal bonding interactions have been used to generate a number of unique supramolecular assemblies with fascinating functions. We presented here a new class of gold(I)-containing metallosupramolecular cages and cage-built two-dimensional (2-D) arrays of {Au8L2}n (n = 1 or ∞, L = tetrakis-dithiocarbamato-calix[4]arene, TDCC), 1-3, which are constructed from the self-assembly of deep-cavitand calix[4]arene-based supramolecular cages consisting of octanuclear Au(I) motifs. Synchrotron radiation X-ray diffraction structural analyses of 1-3 revealed their quadruple-stranded helicate dimeric cage structure and the presence of 2-D arrays of cages linked together by inter- and intramolecular Au(I)···Au(I) interactions. Electronic absorption and emission studies of complexes 1-3 indicated the occurrence of a programmable self-assembly process in a concentration-dependent stepwise manner with the links built via aurophilic interactions. These novel gold(I) supramolecular cages exhibited green phosphorescence and have been shown to serve as highly selective proof-of-concept luminescent sensors toward Ag(I) cation among various competitive transition-metal ions.

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.

Synthesis and cation-binding studies of gold(I) complexes bearing oligoether isocyanide ligands with ester and amide as linkers.

A series of dinuclear gold(I) isocyanide complexes of bis(alkynyl)calix[4]arene was designed and synthesized, and their photophysical and cation recognition properties were studied. Complex 1, [{calix[4]arene-(OCH2CONH-C6H4C≡C)2}{Au(CN-C6H4O(CH2CH2O)2CH3)}2], was found to show a high selectivity towards Al(3+) in CH2Cl2-MeCN (1 : 1 v/v). Upon addition of Al(3+), drastic changes in the electronic absorption, emission and (1)H NMR spectra were observed. These changes have been attributed to the formation of Au(I)Au(i) interactions induced by the high binding affinity of the amide site for the Al(3+) ion, instead of the high binding affinity expected of the oligoether site for alkali and alkaline earth metal ions. Further studies with the control complex, [{calix[4]arene-(OOC-C6H4C≡C)2}{Au(CN-C6H4O(CH2CH2O)2CH3)}2] (4), indicated that the amide carbonyl oxygen in the flexible pendants is crucial for the binding of Al(3+).

Highly selective ion probe for Al3+ based on Au(I)···Au(I) interactions in a bis-alkynyl calix[4]arene Au(I) isocyanide scaffold.

A bis-alkynyl calix[4]arene Au(I) isocyanide complex has been synthesized and demonstrated to be a selective ion probe for Al(3+) based on Au(I)Au(I) interactions.