Time-domain Raman optical activity spectroscopy

Vibrational chiroptical spectroscopy is a valuable tool for investigating the three-dimensional structure of various biomolecules, such as proteins and nucleic acids, in the solution phase. Since the functions of these biomolecules are closely related to their dynamic behavior, the extension of vibrational chiroptical spectroscopy to time-resolved measurements is a promising approach for elucidating the mechanisms responsible for biological functions. However, the implementation of vibrational chiroptical spectroscopy with an ultrashort pulsed laser source—a crucial step toward time-resolved chiroptical spectroscopy—presents significant technical challenges due to its inherently low signal intensity and the difficulty of precise polarization control. Here, we report a sensitive and effective method to measure vibrational Raman optical activity (ROA) spectra using sub-10-fs pulses, which we call time-domain Raman optical activity (TD-ROA) spectroscopy. Specifically, ROA spectra were obtained by measuring a time-dependent change in circular birefringence accompanied by coherent nuclear wavepacket motion. We performed proof-of-principle TD-ROA measurements with (+)- and (−)- β -pinene in the spectral range from 400 to 1200cm −1 , which shows the capability of the method to discriminate enantiomers. Our approach paves the way for tracking chiral nuclear motion that is correlated to the activation of various biomolecular functions.