Multistate Photochromism in a Ruthenium Complex with Dithienylethene–Acetylide

Abstract

The preparation, characterization, and photochromic properties of the ruthenium(II) vinylidene complex 1o and the ruthenium(II) acetylide complex 2o and its oxidized species 2o+ with one dithienylethene (DTE) unit are described. Complexes 1o and 2o can be mutually transformed upon the addition of base or acid due to the interconversion Ru═C═CH–DTE ⇆ Ru–C≡C–DTE. 2o and its oxidized species 2o+ 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 (1c) → 641 nm (2c+) → 692 nm (2c). The photocyclization/cycloreversion quantum yields are in the order 1 (Φo→c = 0.0066, Φc→o = 0.001) < 2+ (Φo→c = 0.35, Φc→o = 0.012) < 2 (Φo→c = 0.58, Φc→o = 0.019), implying that the photochemical reactivity exhibits the order 1 < 2+ < 2, 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.