ABSTRACT
Two-dimensional spectroscopy is a useful method for studying coupling-induced phenomena such as band splitting and excitation transfer as well as for determining the molecular structure of complex molecules in solution. For a coupled dimer, the existence of cross-peaks is good evidence of coupling between the two constituent chromophores. As an example, by measuring the cross-peak amplitude in the 2D amide I IR spectrum of dipeptide consisting of two peptide bonds, it becomes possible to determine the solution structure of dipeptide, as the vibrational coupling strength between the two amide I local modes has been shown be strongly dependent on the backbone conformation of the dipeptide.1-9 Similarly, for coupled electronic chromophores, not only two singly excited states are energetically separated from each other due to coupling but also the downhill and uphill energy transfers between the two excited states occur in time. The latter effects on the diagonal and cross-peak amplitude when a series of time-resolved 2D spectra are measured.10
