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>

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

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

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