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±·DPA series with X = TMA+ (tetramethylammonium), Na+, Cl–, Br–, and I–. This is accomplished through theoretical analysis of X±·DPA·2D2 vibrational spectra, acquired by predissociation of the weakly bound D2 adducts formed in a 10 K ion trap. DPA binds the weakly coordinating TMA+ ion with an arrangement similar to that of the neutral compound, whereas the smaller Na+ 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.
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