Multistate Photochromism in a Ruthenium Complex with Dithienylethene–Acetylide

Abstract

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