Ultrafast vibrational relaxation and structural dynamics of indigo carmine in dimethyl sulfoxide were examined using femtosecond pump-probe infrared and two-dimensional infrared (2D IR) spectroscopies. Using the intramolecularly hydrogen-bonded C=O and delocalized C=C stretching modes as infrared probes, local structural and dynamical variations of this blue dye molecule were observed. Energy relaxation of the vibrationally excited C=O stretching mode was found to occur through covalent bond to the delocalized aromatic vibrational modes on the time scale of a few picoseconds or less. Vibrational quantum beating was observed in magic-angle pump-probe, anisotropy, and 2D IR cross-peak dynamics, showing an oscillation period of ca. 1010 fs, which corresponds to the energy difference between the C=O and C=C transition frequency (33 cm-1). This confirms a resonant vibrational energy transfer happened between the two vibrators. However, a more efficient energy-accepting mode of the excited C=O stretching was believed to be a nearby combination and/or overtone mode that is more tightly connected to the C=O species. On the structural aspect, dynamical-time-dependent 2D IR spectra reveal an insignificant inhomogeneous contribution to time-correlation relaxation for both the C=O and C=C stretching modes, which is in agreement with the generally believed structural rigidity of such conjugated molecules.
CITATION STYLE
He, X., Yu, P., Zhao, J., & Wang, J. (2017). Efficient Vibrational Energy Transfer through Covalent Bond in Indigo Carmine Revealed by Nonlinear IR Spectroscopy. Journal of Physical Chemistry B, 121(40), 9411–9421. https://doi.org/10.1021/acs.jpcb.7b06766
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