Solid-State and Solution Metallophilic Aggregation of a Cationic [Pt(NCN)L]⁺ Cyclometalated Complex

The noncovalent intermolecular interactions (π–π stacking, metallophilic bonding) of the cyclometalated complexes [Pt­(NCN)­L]⁺X^– (NCN = dipyridylbenzene, L = pyridine (<b>1</b>), acetonitrile (<b>2</b>)) are determined by the steric properties of the ancillary ligands L in the solid state and in solution, while the nature of the counterion X^– (X^– = PF₆^–, ClO₄^–, CF₃SO₃^–) affects the molecular arrangement of <b>2</b>·X in the crystal medium. According to the variable-temperature X-ray diffraction measurements, the extensive Pt···Pt interactions and π-stacking in <b>2</b>·X are significantly temperature-dependent. The variable concentration ¹H and diffusion coefficients NMR measurements reveal that <b>2</b>·X exists in the monomeric form in dilute solutions at 298 K, while upon increase in concentration [Pt­(NCN)­(NCMe)]⁺ cations undergo the formation of the ground-state oligomeric aggregates with an average aggregation number of ∼3. The photoluminescent characteristics of <b>1</b> and <b>2</b>·X are largely determined by the intermolecular aggregation. For the discrete molecules the emission properties are assigned to metal perturbed IL charge transfer mixed with some MLCT contribution. In the case of oligomers <b>2</b>·X the luminescence is significantly red-shifted with respect to <b>1</b> and originates mainly from the ³MMLCT excited states. The emission energies depend on the structural arrangement in the crystal and on the complex concentration in solution, variation of which allows for the modulation of the emission color from greenish to deep red. In the solid state the lability of the ligands L leads to vapor-induced reversible transformation <b>1</b> ↔ <b>2</b> that is accompanied by the molecular reorganization and, consequently, dramatic change of the photophysical properties. Time-dependent density functional theory calculations adequately support the models proposed for the rationalization of the experimental observations

Sky-Blue Luminescent Au^I–Ag^I Alkynyl-Phosphine Clusters

Treatment of the (AuC₂R)_<i>n</i> acetylides with phosphine ligand 1,4-bis­(diphenylphosphino)­butane (PbuP) and Ag⁺ ions results in self-assembly of the heterobimetallic clusters of three structural types depending on the nature of the alkynyl group. The hexadecanuclear complex [Au₁₂Ag₄(C₂R)₁₂(PbuP)₆]⁴⁺ (<b>1</b>) is formed for R = Ph, and the octanuclear species [Au₆Ag₂(C₂R)₆(PbuP)₃]²⁺ adopting two structural arrangements in the solid state were found for the aliphatic alkynes (R = Bu^t (<b>2</b>), 2-propanolyl (<b>3</b>), 1-cyclohexanolyl (<b>4</b>), diphenylmethanolyl (<b>5</b>), 2-borneolyl (<b>6</b>)). The structures of the compounds <b>1</b>–<b>4</b> and <b>6</b> were determined by single crystal X-ray diffraction analysis. The NMR spectroscopic studies revealed complicated dynamic behavior of <b>1</b>–<b>3</b> in solution. In particular, complexes <b>2</b> and <b>3</b> undergo reversible transformation, which involves slow interconversion of two isomeric forms. The luminescence behavior of the titled clusters has been studied. All the compounds exhibit efficient sky-blue room-temperature phosphorescence both in solution and in the solid state with maximum quantum yield of 76%. The theoretical DFT calculations of the electronic structures demonstrated the difference in photophysical properties of the compounds depending on their structural topology

Sky-Blue Luminescent Au^I–Ag^I Alkynyl-Phosphine Clusters

Treatment of the (AuC₂R)_<i>n</i> acetylides with phosphine ligand 1,4-bis­(diphenylphosphino)­butane (PbuP) and Ag⁺ ions results in self-assembly of the heterobimetallic clusters of three structural types depending on the nature of the alkynyl group. The hexadecanuclear complex [Au₁₂Ag₄(C₂R)₁₂(PbuP)₆]⁴⁺ (<b>1</b>) is formed for R = Ph, and the octanuclear species [Au₆Ag₂(C₂R)₆(PbuP)₃]²⁺ adopting two structural arrangements in the solid state were found for the aliphatic alkynes (R = Bu^t (<b>2</b>), 2-propanolyl (<b>3</b>), 1-cyclohexanolyl (<b>4</b>), diphenylmethanolyl (<b>5</b>), 2-borneolyl (<b>6</b>)). The structures of the compounds <b>1</b>–<b>4</b> and <b>6</b> were determined by single crystal X-ray diffraction analysis. The NMR spectroscopic studies revealed complicated dynamic behavior of <b>1</b>–<b>3</b> in solution. In particular, complexes <b>2</b> and <b>3</b> undergo reversible transformation, which involves slow interconversion of two isomeric forms. The luminescence behavior of the titled clusters has been studied. All the compounds exhibit efficient sky-blue room-temperature phosphorescence both in solution and in the solid state with maximum quantum yield of 76%. The theoretical DFT calculations of the electronic structures demonstrated the difference in photophysical properties of the compounds depending on their structural topology

Supramolecular Au^I–Cu^I Complexes as New Luminescent Labels for Covalent Bioconjugation

Two new supramolecular organometallic complexes, namely, [Au₆Cu₂(C₂C₆H₄<b>CHO</b>)₆(PPh₂C₆H₄PPh₂)₃]­(PF₆)₂ and [Au₆Cu₂(C₂C₆H₄<b>NCS</b>)₆(PPh₂C₆H₄PPh₂)₃]­(PF₆)₂, with highly reactive aldehyde and isothiocyanate groups have been synthesized and characterized using X-ray crystallography, ESI mass spectrometry, and NMR spectroscopy. The compounds obtained demonstrated bright emission in solution with the excited-state lifetime in microsecond domain both under single- and two-photon excitation. The luminescent complexes were found to be suitable for bioconjugation in aqueous media. In particular, they are able to form the covalent conjugates with proteins of different molecular size (soybean trypsin inhibitor, human serum albumin, rabbit anti-HSA antibodies). The conjugates demonstrated a high level of the phosphorescent emission from the covalently bound label, excellent solubility, and high stability in physiological media. The highest quantum yield, storage stability, and luminance were detected for bioconjugates formed by covalent attachment of the aldehyde-bearing supramolecular Au^I–Cu^I complex. The measured biological activity of one of the labeled model proteins clearly showed that introduced label did not prevent the biorecognition and specific protein–protein complex formation that was extremely important for the application of the conjugates in biomolecular detection and imaging

Coordination to Imidazole Ring Switches on Phosphorescence of Platinum Cyclometalated Complexes: The Route to Selective Labeling of Peptides and Proteins via Histidine Residues

In this study, we have shown that substitution of chloride ligand for imidazole (Im) ring in the cyclometalated platinum complex Pt­(phpy)­(PPh₃)Cl (<b>1</b>; phpy, 2-phenylpyridine; PPh₃, triphenylphosphine), which is nonemissive in solution, switches on phosphorescence of the resulting compound. Crystallographic and nuclear magnetic resonance (NMR) spectroscopic studies of the substitution product showed that the luminescence ignition is a result of Im coordination to give the [Pt­(phpy)­(Im)­(PPh₃)]Cl complex. The other imidazole-containing biomolecules, such as histidine and histidine-containing peptides and proteins, also trigger luminescence of the substitution products. The complex <b>1</b> proved to be highly selective toward the imidazole ring coordination that allows site-specific labeling of peptides and proteins with <b>1</b> using the route, which is orthogonal to the common bioconjugation schemes via lysine, aspartic and glutamic acids, or cysteine and does not require any preliminary modification of a biomolecule. The utility of this approach was demonstrated on (i) site-specific modification of the ubiquitin, a small protein that contains only one His residue in its sequence, and (ii) preparation of nonaggregated HSA-based Pt phosphorescent probe. The latter particles easily internalize into the live HeLa cells and display a high potential for live-cell phosphorescence lifetime imaging (PLIM) as well as for advanced correlation PLIM and FLIM experiments