Quantifying Intrinsic Ion-Driven Conformational Changes in Diphenylacetylene Supramolecular Switches with Cryogenic Ion Vibrational Spectroscopy
2013-07-25T00:00:00Z (GMT) by
We report how two flexible diphenylacetylene (DPA) derivatives distort to accommodate both cationic and anionic partners in the binary X<sup>±</sup>·DPA series with X = TMA<sup>+</sup> (tetramethylammonium), Na<sup>+</sup>, Cl<sup>–</sup>, Br<sup>–</sup>, and I<sup>–</sup>. This is accomplished through theoretical analysis of X<sup>±</sup>·DPA·2D<sub>2</sub> vibrational spectra, acquired by predissociation of the weakly bound D<sub>2</sub> adducts formed in a 10 K ion trap. DPA binds the weakly coordinating TMA<sup>+</sup> ion with an arrangement similar to that of the neutral compound, whereas the smaller Na<sup>+</sup> ion breaks all intramolecular H-bonds yielding a structure akin to the transition state for interconversion of the two conformations in neutral DPA. Halides coordinate to the urea NH donors in a bidentate H-bonded configuration analogous to the single intramolecular H-bonded motif identified at high chloride concentrations in solution. Three positions of the “switch” are thus identified in the intrinsic ion accommodation profile that differ by the number of intramolecular H-bonds (0, 1, or 2) at play.