Journal Highlight: Refining the interpretation of near-infrared band shapes in a polyynediyl molecular wire

Refining the interpretation of near-infrared band shapes in a polyynediyl molecular wire

Chemistry - A European Journal, 2013, 19, 9780-9784
Matthias Parthey, Josef B. G. Gluyas, Phil A. Schauer, Dmitry S. Yufit, Judith A. K. Howard, Martin Kaupp, Paul J. Low

Abstract: Polyynediyl bridged systems have attracted attention for more than two decades, with early synthetic efforts complemented more recently by experimental and computational investigations of electronic structure. Polyynediyl complexes serve as models of the linear carbon allotrope carbyne and permit investigations of intramolecular electron transfer reactions and mixed-valence characteristics. In this work, the near-IR spectrum of [{Ru(PPh₃)₂Cp}₂(μ-C≡CC≡C)]⁺ [1⁺], which has a high-energy shoulder, has been reexamined to show that the presence of rotamers is also a crucial variable that may influence the appearance of the intervalence charge transfer band and the underlying electronic structure. The NIR band envelope observed for [1]+ features two transition envelopes with distinct electronic character (π–π* and MLCT) arising from a distribution of conformers in solution. The observed NIR absorption profile of [1]+ is in good agreement with the predictions based on a relaxed rotamer scan and well-matched with the results from the three fully optimised structures trans-[1]⁺, perp-[1]⁺ and cis-[1]⁺. An accurate interpretation of the NIR spectrum of [1]⁺ must therefore allow for the different spectroscopic properties of the various rotameric forms.

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