Simultaneous observation of multiple ultrafast dynamic processes for a dicarbonyl compound by two-dimensional infrared spectroscopy

Two-dimensional infrared spectroscopy (2D IR) has been used to simultaneously observe multiple ultrafast dynamic processes for a dicarbonyl compound, 3-Carbethoxy-2-piperidone, consisting of two carbonyl (C=O) groups, an ester carbonyl and a cis-amide, in methanol. Waiting time-dependent 2D IR spectra revealed chemical exchange between different configurations of hydrogen-bonded networks around each C=O group, spectral diffusion of C=O modes caused by solvent hydrogen-bond fluctuations, and vibrational energy transfer between the ester C=O and the cis-amide. The processes were faster at higher temperatures, although a relatively weak dependence of energy transfer rate on change in temperature was observed. All these dynamic processes occur in the timescale of picoseconds and cannot be identified by conventional linear absorption spectroscopy. This demonstrative work paves the way for understanding fast chemical reactions in organic solvents at the atomic level.clos