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

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

Phosphorescent PtAu₂ Complexes with Differently Positioned Carbazole–Acetylide Ligands for Solution-Processed Organic Light-Emitting Diodes with External Quantum Efficiencies of over 20%

The utilization of phosphorescent metal cluster complexes as new types of emitting materials in organic light-emitting diodes (OLEDs) is becoming an alternative and viable approach for achieving high-efficiency electroluminescence. We report herein the design of cationic PtAu₂ cluster complexes with differently positioned 9-phenylcarbazole–acetylides to serve as phosphorescent emitters in OLEDs. The rigid structures of PtAu₂ complexes cause intense phosphorescence with quantum yields of over 85%, which originates from ³[π­(phenylcarbazole–acetylide) → π*­(dpmp)] ligand-to-ligand and ³[π­(phenylcarbazole–acetylide) → p/s­(PtAu₂)] ligand-to-metal charge-transfer triplet excited states. When 8 wt % PtAu₂ is doped to blended host materials of TCTA and OXD-7 (2:1 weight ratio) as light-emitting layers, solution-processed OLEDs give a current efficiency of 78.2 cd A^–1 and an external quantum efficiency (EQE) of 21.5% at a practical luminance of 1029 cd m^–2 with a slow efficiency roll-off upon increasing luminance. This represents the best device performance and the highest efficiency recorded at practical luminance for solution-processed OLEDs

Structures and Phosphorescence Properties of Triphosphine-Supported Au₂Ag₂ and Au₈Ag₄ Alkynyl Cluster Complexes

The synthesis, structure, and phosphorescence properties of two families of triphosphine-supported Au­(I)–Ag­(I) heteronuclear alkynyl cluster complexes with unprecedented Au₂Ag₂ and Au₈Ag₄ cluster structures are described. The phosphorescence emission over the whole visible light region was systematically tuned through modification of the electronic effects in aromatic acetylide ligands to attain bright phosphorescence with different luminescent colors. Introduction of electron-withdrawing CF₃ to phenylacetylides results in the emission spectral blue-shift, while it shows progressive red-shift upon introducing electron-donating Bu^t, OMe, or NMe₂. As demonstrated from both experimental and theoretical studies, the phosphorescence arises primarily from ³LLCT/³IL and Au₂Ag₂/Au₈Ag₄ cluster-centered ³[d→p] transitions

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

Modulating Stepwise Photochromism in Platinum(II) Complexes with Dual Dithienylethene–Acetylides by a Progressive Red Shift of Ring-Closure Absorption

To modulate stepwise photochromism by shifting ring-closure absorption of the dithienylethene (DTE) moiety, <i>trans</i>-Pt­(PEt₃)₂(CC-DTE)₂ [CC-DTE = L1o (<b>1oo</b>), L2o (<b>2oo</b>), L3o (<b>3oo</b>), and L4o (<b>4oo</b>)] and <i>cis</i>-Pt­(PEt₃)₂(L4o)₂ (<b>5oo</b>) with two identical DTE–acetylides were elaborately designed. With the gradual red shift of ring-closure absorption for L1c (441 nm) → L2c (510 nm) → L3c (556 nm) → L4c (602 nm), stepwise photochromism is increasingly facilitated in <i>trans</i>-Pt­(PEt₃)₂(CC-DTE)₂ following <b>1oo</b> → <b>2oo</b> → <b>3oo</b> → <b>4oo</b>. The conversion percentage of singly ring-closed <b>2co</b>–<b>4co</b> to dually ring-closed <b>2cc</b>–<b>4cc</b> at the photostationary state is progressively increased in the order <b>1cc</b> (0%) → <b>2cc</b> (18%) → <b>3cc</b> (67%) → <b>4cc</b> (100%). Compared with trans-arranged <b>4oo</b>, stepwise photochromism in the corresponding cis-counterpart <b>5oo</b> is less pronounced, ascribed to either direct conversion of <b>5oo</b> to <b>5cc</b> or rapid conversion of <b>5co</b> to <b>5cc</b>. The progressively facile stepwise photocyclization following <b>2oo</b> → <b>3oo</b> → <b>4oo</b> is reasonably interpreted by gradually enhanced transition character involving LUMO+1, which is the only unoccupied frontier orbital responsible for further photocyclization of singly ring-closed <b>2co</b>–<b>4co</b>

Spectroscopic and Phosphorescent Modulation in Triphosphine-Supported PtAg₂ Heterotrinuclear Alkynyl Complexes

A series of highly phosphorescent PtAg₂ heterotrinuclear alkynyl complexes with bis­(diphenylphosphinomethyl)­phenylphosphine (dpmp) were prepared and characterized structurally. The solution phosphorescence with various emitting colors is systematically modulated by modifying substituents as well as π-conjugated systems in aromatic acetylides. The crystals, powders, or films exhibit reversible stimuli-responsive phosphorescence changes upon exposure to vapor of MeCN, pyridine, DMF, etc., resulting from perturbation of d⁸-d¹⁰ metallophilic interaction in the excited states as a consequence of the formation/disruption of Ag–solvent bonds. Both experimental and time-dependent density functional theory (TD-DFT) studies demonstrate that d⁸-d¹⁰ metallophilic interaction exerts a crucial role on phosphorescent characteristics due to the PtAg₂ cluster-based ³[d → p] state. This study affords a paradigm for phosphorescence modulation in d⁸–d¹⁰ heteronuclear complexes

Multistate Photochromism in a Ruthenium Complex with Dithienylethene–Acetylide

The preparation, characterization, and photochromic properties of the ruthenium­(II) vinylidene complex <b>1o</b> and the ruthenium­(II) acetylide complex <b>2o</b> and its oxidized species <b>2o</b>⁺ with one dithienylethene (DTE) unit are described. Complexes <b>1o</b> and <b>2o</b> can be mutually transformed upon the addition of base or acid due to the interconversion RuCCH–DTE ⇆ Ru–CC–DTE. <b>2o</b> and its oxidized species <b>2o</b>⁺ can be interconverted through a reversible redox process. It is found that the ring-closing absorption band of DTE shows a progressive red shift in the order 628 nm (<b>1c</b>) → 641 nm (<b>2c</b>⁺) → 692 nm (<b>2c</b>). The photocyclization/cycloreversion quantum yields are in the order <b>1</b> (Φ_o→c = 0.0066, Φ_c→o = 0.001) < <b>2</b>⁺ (Φ_o→c = 0.35, Φ_c→o = 0.012) < <b>2</b> (Φ_o→c = 0.58, Φ_c→o = 0.019), implying that the photochemical reactivity exhibits the order <b>1</b> < <b>2</b>⁺ < <b>2</b>, coinciding well with the progressively increased electronic density at the reactive carbon atoms. The interconversion among six states is clearly demonstrated by NMR, UV–vis–near-IR, and IR spectral, electrochemical, and computational studies

Synthesis and characterization of emissive mononuclear Cu(I) complexes with 5-<i>tert</i>-butyl-3-(pyrimidine-2-yl)-1<i>H</i>-1,2,4-triazole

<div><p>A new series of mononuclear copper(I) halide complexes possessing 5-<i>tert</i>-butyl-3-(pyrimidine-2-yl)-1<i>H</i>-1,2,4-triazole (bpmtzH) and PPh₃, Cu(bpmtzH)(PPh₃)X (X = I (<b>1</b>); Br (<b>2</b>); Cl (<b>3</b>)), have been synthesized and characterized. As revealed via X-ray crystallography, <b>1–3</b> show a chiral, distorted tetrahedral N₂PX arrangement, in which bpmtzH is a neutral bidentate chelating ligand using the 4-N of the 1,2,4-triazolyl ring and one N donor from the 2-pyrimidyl ring, consistent with the computational results. A comparatively weak low-energy absorption tail is observed between 320 and 450 nm for CH₂Cl₂ solutions of <b>1–3</b> at room temperature, ascribing to charge-transfer transitions with appreciable metal-to-ligand charge transfer (MLCT) character. Complexes <b>1–3</b> in the solid state have good luminescence at ambient temperature, although they are non-emissive in solution. The solid-state emission, most likely originating from both ³MLCT and ³XLCT transitions, can be modulated via alteration of the halide bound to {Cu(bpmtzH)(PPh₃)} motif.</p></div