Heterovibrational Interactions, Cooperative Hydrogen Bonding, and Vibrational Energy Relaxation Pathways in a Rotaxane

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• 作者：Pavol Bodis ; Rutger Timmer ; Sergey Yeremenko ; Wybren Jan Buma ; Jeffrey S. Hannam ; David A. Leigh ; Sander Woutersen
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：May 10, 2007
• 年：2007
• 卷：111
• 期：18
• 页码：6798 - 6804
• 全文大小：832K
• 年卷期：v.111,no.18(May 10, 2007)
• ISSN：1932-7455

文摘

Femtosecond two-color vibrational pump-probe spectroscopy is used to investigate the interaction betweenthe NH- and CO-stretch vibrations in a rotaxane composed of a benzylic amide macrocycle mechanicallylocked onto a succinamide-based thread. From the transient absorption spectrum, we obtain the crossanharmonicities and cross-peak anisotropies arising from the NH(macrocycle)/CO(macrocycle) and NH(macrocycle)/CO(thread) interactions. The cross-peak anisotropies are used to determine angles between NHand CO bonds in the macrocycle and the thread, providing structural information with picosecond temporalresolution. The CO and NH groups that form the macrocycle-thread hydrogen bonds are found to interactmuch more strongly than the CO and NH groups in other molecular systems containing the same NH···OChydrogen-bond motif. We attribute this enhancement of the NH/CO anharmonic interaction to a cooperativeeffect, by which the two ring-thread hydrogen bonds sharing a hydrogen-bond acceptor mutually amplifyeach other. The relaxation dynamics of the NH/CO cross peaks has also been investigated. Surprisingly, theNH/CO cross peak observed upon exciting the NH-stretch mode decays much more slowly than thecorresponding diagonal NH-stretch peak. This can be explained by the presence of an intermediate state thatbecomes populated in the NH-stretch vibrational relaxation and that is coupled to the CO-stretch mode. Ourresults demonstrate that NH/CO heterovibrational 2D-IR spectroscopy is well suited to observe the elementaryhydrogen-bond making and breaking steps involved in the motion of rotaxane-based molecular devices.