Structural Characterization and Luminescence Properties of a Triphosphine-Stabilized Ag₁₆Cu₉ Heterometallic Alkynyl Cluster

A triphosphine-stabilized Ag₁₆Cu₉ heterometallic alkynyl cluster complex was prepared by the reaction of polymeric silver­(I) (4-<i>tert</i>-butylphenyl)­acetylide with a copper­(I) dpepp (dpepp = bis­(2-(diphenylphosphino)­ethyl)­phenylphosphine) complex and characterized by X-ray crystallography. This Ag₁₆Cu₉ heterometallic alkynyl complex exhibits an unprecedented structural topology stabilized by three auxiliary triphosphine ligands. The (4-<i>tert</i>-butylphenyl)­acetylide exhibits five types of asymmetric bonding modes, including μ-η¹, μ-η¹(σ):η²(π), μ₃-η¹, μ₃-η¹(σ):η¹(σ):η²(π), and η¹-μ₄. This Ag₁₆Cu₉ complex exhibits visible to near-infrared luminescence in both fluid CH₂Cl₂ solution and the solid state

Tetranuclear Gadolinium(III) Porphyrin Complex as a Theranostic Agent for Multimodal Imaging and Photodynamic Therapy

We describe herein the elaborate design of a Gd­(III)–porphyrin complex as a theranostic agent for multimodal imaging and photodynamic therapy. Far-red-emitting (665 nm) and high relaxivity (14.1 mM^–1 s^–1) with 107% increase upon binding to HSA (human serum albumin) (29.2 mM^–1 s^–1) together with efficiently generating singlet oxygen upon exposure to far-red light irradiation at 650 ± 20 nm demonstrate that this Gd­(III)–porphyrin complex with four Gd­(III)–DTTA units bound to tetraphenylporphyrin acts as a potentially theranostic agent with excellent performance for magnetic resonance imaging, optical imaging, and photodynamic therapy

Multiphotochromism in an Asymmetric Ruthenium Complex with Two Different Dithienylethenes

An asymmetric bis­(dithienylethene-acetylide) ruthenium­(II) complex <i>trans</i>-Ru­(dppe)₂(L1o)­(L2o) (<b>1oo</b>) incorporating two different dithienylethene–acetylides (L1o and L2o) was designed to modulate multistate photochromism in view of the well separated ring-closing absorption bands between L1o and L2o. Upon irradiation with appropriate wavelengths of light, complex <b>1</b> undergoes stepwise photocyclization and selective photocycloreversion to afford four states (<b>1oo</b>, <b>1co</b>, <b>1oc</b>, and <b>1cc</b>). As a contrast, symmetric complexes <i>trans</i>-Ru­(dppe)₂(L1o)₂ (<b>2oo</b>) and <i>trans</i>-Ru­(dppe)₂(L2o)₂ (<b>3oo</b>) with two identical dithienylethene-acetylides were synthesized, and the corresponding photochromic behavior was investigated. The photochromic properties of the oxidized species (<b>1oo</b>^<b>+</b>/<b>1co</b>^<b>+</b>/<b>1oc</b>^<b>+</b>/<b>1cc</b>^<b>+</b>, <b>2oo</b>^<b>+</b>/<b>2co</b>^<b>+</b>/<b>2cc</b>^<b>+</b>, and <b>3oo</b>^<b>+</b>/<b>3co</b>^<b>+</b>/<b>3cc</b>^<b>+</b>) were also investigated. The ring-closing absorption bands of one-electron oxidized species <b>1oo</b>^<b>+</b>, <b>2oo</b>^<b>+</b>, and <b>3oo</b>^<b>+</b> show obvious blue shifts relative to those of <b>1oo</b>, <b>2oo</b>, and <b>3oo</b>, respectively. The ring-closing absorption bands in both neutral and oxidized species grow progressively following <b>oo</b> → <b>oc</b>/<b>co</b> → <b>cc</b> and <b>oo</b>^<b>+</b> → <b>oc</b>^<b>+</b>/<b>co</b>^<b>+</b> → <b>cc</b>^<b>+</b>. As revealed by spectroscopic, electrochemical, and computational studies, complex <b>1</b> displays eight switchable states through stepwise photocyclization, selective cycloreversion, and a reversible redox process

Electrochemical, Spectroscopic, and Theoretical Studies on Diethynyl Ligand Bridged Ruthenium Complexes with 1,3-Bis(2-pyridylimino)isoindolate

A series of ruthenium acetylide complexes [Ru­(BPI)­(PPh₃)₂(CCR)] (BPI = 1,3-bis­(2-pyridylimino)­isoindolate; R = −C₆H₅ (<b>2</b>), −Cp₂Fe (<b>3a</b>), −C₆H₄C₆H₄CCCp₂Fe (<b>3b</b>)) and bis­(acetylide)-linked binuclear ruthenium complexes [{Ru­(BPI)­(PPh₃)₂}₂(CCRCC)] (R = none (<b>4</b>), 1,4-benzenediyl (<b>5</b>), 1,4-naphthalenediyl (<b>6</b>), 9,10-anthracenediyl (<b>7</b>)) were synthesized and characterized by ESI-MS spectrometry, IR, ¹H and ³¹P NMR, and UV–vis–near-IR spectroscopy, and cyclic and differential pulse voltammetry. Oxidation of <b>3</b>–<b>7</b> with 1 equiv of ferrocenium perchlorate afforded the corresponding one-electron-oxidized complexes <b>3</b>⁺–<b>7</b>⁺. In contrast to the case for <b>3a</b>^<b>+</b>, where spin density is localized at the Fe center due to moderate electronic communication between Ru^II and Fe^III centers along the Ru–CC–Cp₂Fe backbone, the spin density is primarily populated on Ru for <b>3b</b>^<b>+</b> without an appreciable electronic interaction between Ru^III and Fe^II across the quite long bridging system RuCCC₆H₄C₆H₄CCCp₂Fe. For bis­(acetylide)-linked binuclear ruthenium complexes <b>4</b>–<b>7</b>, electrochemical, UV–vis–near-IR spectral and TD-DFT computational studies reveal that electronic delocalization along the bridging RuCCRCCRu backbone is highly dependent on the R spacer. It is demonstrated that with the gradual increase of a π-conjugated system in aromatic R spacer, the electronic delocalization shows progressive enhancement along the Ru–CCRCC–Ru backbone due to an increasing participation of the bridging ligand. <b>4</b>⁺ displays highly electronically delocalized behavior, whereas <b>5</b>⁺–<b>7</b>⁺ are on the borderline of electronic delocalization

Structural and Photophysical Studies on Geometric (Er₂Yb₂/Yb₂Er₂) and Configurational (EuTb₃/Eu₃Tb) Isomers of Heterotetranuclear Lanthanide(III) Complexes

Heterotetranuclear geometrical (Er₂Yb₂/Yb₂Er₂) and configuational (EuTb₃/Eu₃Tb) isomeric lanthanide­(III) complexes have been synthesized and characterized by spectroscopy as well as X-ray crystallography. The geometric Er₂Yb₂/Yb₂Er₂ isomers exhibit dual emissions from both erbium­(III) and ytterbium­(III) ions. For the EuTb₃/Eu₃Tb configurational isomers, the Tb^III subunits transfer energy to the Eu^III centers in the EuTb₃ complex, whereas the Tb^III ion in the TbEu₃ complex serves mainly as a structural stabilizer

Photophysical and Electroluminescent Properties of PtAg₂ Acetylide Complexes Supported with <i>meso</i>- and <i>rac</i>-Tetraphosphine

1,2-Bis­[[(diphenylphosphino)­methyl]­(phenyl)­phosphino]­ethane (dpmppe) was prepared as a new tetraphosphine, and the corresponding <i>rac</i> and <i>meso</i> stereoisomers were successfully separated in view of their solubility difference in acetone. The substitution of PPh₃ into Pt­(PPh₃)₂(CCR)₂ (R = aryl) with <i>rac</i>- or <i>meso</i>-dpmppe gives Pt­(<i>rac</i>-dpmppe)­(CCR)₂ or Pt­(<i>meso</i>-dpmppe)­(CCR)₂, respectively. Using Pt­(<i>rac</i>-dpmppe)­(CCR)₂ or Pt­(<i>meso</i>-dpmppe)­(CCR)₂ as a precursor, PtAg₂ heterotrinuclear cluster complexes were synthesized and characterized by X-ray crystallography. Depending on the conformations of tetraphosphine, the structures of PtAg₂ complexes supported with <i>rac</i>- and <i>meso</i>-dpmppe are quite different. The higher molecular rigidity of <i>rac</i>-dpmppe-supported PtAg₂ complexes results in stronger phosphorescent emission than that of PtAg₂ species with <i>meso</i>-dpmppe. The high phosphorescent quantum yields (as high as 90.5%) in doping films warrant these PtAg₂ complexes as excellent phosphorescent dopants in organic light-emitting diodes (OLEDs). The peak current and external quantum efficiencies in solution-processed OLEDs are 61.0 cd A^–1 and 18.1%, respectively. Electroluminescence was elaborately modulated by modifying the substituent in aromatic acetylide and the conformations in tetraphosphine so as to achieve cyan, green, green-yellow, yellow, and orange-red emission

Luminescent Vapochromism Due to a Change of the Ligand Field in a One-Dimensional Manganese(II) Coordination Polymer

The reactions of MnBr₂ and ethane-1,2-diylbis­(diphenylphosphine oxide) (dppeO₂) in dichloromethane–methanol solutions gave colorless crystals with the general chemical formulas [MnBr₂(dppeO₂)]_<i>n</i> (<b>1</b>), [MnBr₂(dppeO₂)­(DMF)]_<i>n</i> (<b>1a</b>), [Mn­(dppeO₂)₃]­[MnBr₄] (<b>2</b>), and Mn₂Br₄(dppeO₂)₂ (<b>3</b>) depending on the crystallization conditions. Compounds <b>1</b> and <b>1a</b> display one-dimensional chain structures composed of Mn­(II) ions linked by bridging dppeO₂ to exhibit tetrahedral (<b>1</b>) or trigonal-bipyramidal (<b>1a</b>) coordination geometry, whereas <b>3</b> exhibits a cyclic dinuclear structure with two Mn­(II) centers bridged by double dppeO₂ to adopt tetrahedral geometry. Compound <b>2</b> consists of octahedrally coordinated cation [Mn­(dppeO₂)₃]²⁺ and tetrahedrally arranged anion [MnBr₄]^2–. While <b>1</b> and <b>3</b> in crystalline and powder states are highly luminescent with green emission bands centered at ca. 510 nm, <b>2</b> shows intense orange luminescence peaking at 594 nm. Upon exposure of <b>1</b> to <i>N</i>,<i>N</i>-dimethylformamide vapor, the green emission centered at 510 nm is converted to red luminescence peaking at 630 nm, ascribed to the formation of DMF-coordinated compound <b>1a</b> with a trigonal-bipyramidal ligand field, as demonstrated by X-ray crystallography. Red-emitting <b>1a</b> could be reverted to the original green-emitting <b>1</b> with a tetrahedral ligand field upon heat at 160 °C, and such a reversible conversion could be perfectly repeated for several cycles. A new mechanism of luminescent vapochromism is thus proposed because of the reversible conversion of ligand fields in manganese­(II) complexes

Zn²⁺ Responsive Bimodal Magnetic Resonance Imaging and Fluorescent Imaging Probe Based on a Gadolinium(III) Complex

A Zn²⁺-responsive bimodal magnetic resonance imaging (MRI) and luminescence imaging probe GdL was synthesized. The relaxivity and luminescence properties were examined. In the presence of 0.5 equiv of Zn²⁺, the longitudinal relaxivity is increased from 3.8 mM^–1 s^–1 to 5.9 mM^–1 s^–1 at 23 MHz and 25 °C with 55% enhancement, whereas the fluorescence exhibits a 7-fold increase. The Zn²⁺ responsive imaging probe shows favorable selectivity and tolerance over a variety of biologically relevant anions and metal ions in physiological pH range for both relaxivity and luminescence. In vitro phantom images and confocal fluorescence images in living cells show that the bimodal Zn²⁺ probe can effectively enhance <i>T</i>₁-weighted imaging contrast and luminescence imaging effect through Zn²⁺ coordination with excellent cellmembrane permeability and biocompatibility. Spectral and electrospray ionization mass spectrometry (ESI-MS) studies indicate that two different Zn²⁺-bound species, (GdL)₂Zn and GdLZn, are formed when 0.5 and 1 equiv of Zn²⁺ are bound to GdL complex, respectively. Crystal structural determination and dysprosium-induced ¹⁷O NMR shift (DIS) experiment demonstrate that the increased molecular weight and the improved molecular rigidity upon complexation of Zn²⁺ with GdL is the primary factor for relaxivity enhancement. Significant enhancement of the luminescence is due to a heavy atom effect and much increased molecular rigidity upon Zn²⁺ binding to 8-sulfonamidoquinoline chromophore

Vapochromic and Mechanochromic Phosphorescence Materials Based on a Platinum(II) Complex with 4-Trifluoromethylphenylacetylide

Planar platinum­(II) complex Pt­(Me₃SiCCbpyCCSiMe₃)­(CCC₆H₄CF₃-4)₂ (<b>6</b>) with 5,5′-bis­(trimethylsilylethynyl)-2,2′-bipyridine and 4-trifluoromethylphenylacetylide exhibits remarkable luminescence vapochromic and mechanochromic properties and a thermo-triggered luminescence change. Solid-state <b>6</b> is selectively sensitive to vapors of oxygen-containing volatile compounds such as tetrahydrofuran (THF), dioxane, and tetrahydropyrane (THP) with phosphorescence vapochromic response red shifts from 561 and 608 nm to 698 nm (THF), 689 nm (dioxane), and 715 nm (THP), respectively. Upon being mechanically ground, desolvated <b>6</b>, <b>6</b>·CH₂Cl₂, and <b>6</b>·¹/₂CH₂ClCH₂Cl exhibit significant mechanoluminescence red shifts from 561 and 608 nm to 730 nm, while vapochromic crystalline species <b>6</b>·THF, <b>6</b>·dioxane, or <b>6</b>·THP affords a mechanoluminescence blue shift from 698 nm (THF), 689 nm (dioxane), or 715 nm (THP) to 645 nm, respectively. When the compounds are heated, a thermo-triggered luminescence change occurs, in which bright yellow luminescence at 561 and 608 nm turns to red luminescence at 667 nm with a drastic red shift. The multi-stimulus-responsive luminescence switches have been monitored by the changes in emission spectra and X-ray diffraction patterns. Both X-ray crystallographic and density functional theory studies suggest that the variation in the intermolecular Pt–Pt interaction is the key factor in inducing an intriguing luminescence switch

Gold(I)-Coordination Triggered Multistep and Multiple Photochromic Reactions in Multi-Dithienylethene (DTE) Systems

The preparation, characterization, and photochromic properties of a mononuclear gold­(I) complex (<b>1oo</b>) with two identical DTE-acetylides and a dinuclear gold­(I) complex (<b>2ooo</b>) with both DTE-acetylide and DTE-diphosphine are described. Both gold­(I) complexes exhibit multistep and multiple photocyclization/cycloreversion reactions. Particularly, four-state and four-color photochromic switch is successfully achieved for the dinuclear gold­(I) complex upon irradiation with appropriate wavelengths of light. In contrast, fully ring-closed form is unattained through multiple photocyclization for the two corresponding model organic compounds coupling with the same DTE units as gold­(I) complexes but without gold­(I)-participation. It is demonstrated that coordination of gold­(I) ion to DTE-acetylides exerts indeed a crucial role in achieving stepwise and selective photocyclization and cycloreversion reactions for both gold­(I) complexes, in which the coordinated gold­(I) atom acts as an effective “barrier” to prohibit intramolecular energy transfer between multi-DTE moieties