Observing Rotaxane Shuttling with Two-Dimensional Femtosecond Vibrational Spectroscopy

Femtosecond two-dimensional infrared spectroscopy has been used to investigate the coupling between the NH stretch vibrational modes of NH groups in the macrocycle and thread of a benzylic amide rotaxane as a potential time-resolved indicator of rotaxane shuttling. The peptide was used to test the two-dimensional infrared setup. We were able to observe the coupling between the asymmetric and the symmetric stretch of the free amine group in two different conformers proving the system was capable of measuring the interaction between coupled NH stretch modes. Broadband pump-probe experiments have been conducted to probe the dynamics of the rotaxane in the NH stretch region. Two-dimensional infrared spectra were made of the rotaxane. A possible cross-peak was found between the NH stretch modes. A definitive crosspeak has yet to be observed. The performance of a specialised electrochemical IR sample cell was tested and was found to be suitable for the conducting of 2D IR while performing electro chemistry on the sample.