Multistate Photochromism in a Ruthenium Complex with
Dithienylethene–Acetylide
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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><sup>+</sup> 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 RuCCH–DTE
⇆ Ru–CC–DTE. <b>2o</b> and its
oxidized species <b>2o</b><sup>+</sup> 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><sup>+</sup>) → 692 nm (<b>2c</b>). The photocyclization/cycloreversion
quantum yields are in the order <b>1</b> (Φ<sub>o→c</sub> = 0.0066, Φ<sub>c→o</sub> = 0.001) < <b>2</b><sup>+</sup> (Φ<sub>o→c</sub> = 0.35, Φ<sub>c→o</sub> = 0.012) < <b>2</b> (Φ<sub>o→c</sub> = 0.58,
Φ<sub>c→o</sub> = 0.019), implying that the photochemical
reactivity exhibits the order <b>1</b> < <b>2</b><sup>+</sup> < <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