Ultrafast N-H Vibrational Dynamics of Cyclic Doubly Hydrogen-Bonded Homo- and Heterodimers

Abstract

Hydrogen-bonded interfaces are essential structural elements in biology. Furthermore they can mediate electron transport by coupling the electron to proton transfer within the interface. The specific hydrogen-bonding configuration and strength have a large impact on the proton transfer, which exchanges the hydrogen bonded donor and acceptor species (i.e. NH---O → N---HO. Modulations of the hydrogen-bonding environment, such as the hydrogen-bond stretch and twist modes, affect the proton transfer dynamics. Here we present transient grating and echo peak shift measurements of the NH stretch vibrations of four doubly hydrogen-bonded cyclic dimers in their electronic ground state. The equilibrium vibrational dynamics exhibit strong coherent modulations that we attribute to coupling of the high-frequency NH vibration to the low frequency inter-dimer stretch and twist modes and not to interference between multiple Fermi-resonances that dominate the substructure of the linear spectra.