123rd General Meeting of the KCS

Type Oral Presentation
Area Oral Presentation for Young Physical Chemists I
Room No. Room 305+306
Time THU 09:50-09:59
Code PHYS1.O-6
Subject Optically active vibrational sum-frequency generation spectroscopy of chiral molecule in isotropic liquid
Authors Taegon Lee, Sanghee Nah, Jun-taek Oh1, Hanju Rhee*
Seoul Center, Korea Basic Science Institute, Korea
1Korea Basic Science Institute, Korea
Abstract Vibrational optical activity (VOA) has proven to be of use in determining absolution configuration of small organic chiral molecule and conformation of biomolecules such as protein and DNA. However, conventional VOA techniques such as vibrational circular dichroism (VCD) and Raman optical activity (ROA) often suffer from the weak signal and huge achiral background problems, which hinder an effective measurement of the chiral signal and thus have limited its wide application. Vibrational sum-frequency generation (VSFG) spectroscopy is a well-known technique that has been used to study vibrational structure and dynamics of molecules on the surface or at the interface, where centrosymmetry is broken. Recently, we developed a femtosecond chiral VSFG technique based on quasi-null achiral background-free measurement. Interestingly, it was shown that an optically active (OA) femtosecond VSFG signal can be generated from chiral molecules in isotropic bulk liquid, not just at the glass/liquid interface. By using a combination of femtosecond (spectrally broad) mid-IR and picosecond (spectrally narrow) visible laser beams, we could obtain the OA VSFG spectra of chiral limonene in the C-H stretching frequency region without any frequency scan. We also found that the stereo-specific vibrational structures of the enantiomers can be distinguished by circular and linear polarization intensity differences (CID and LID) under particular polarization controls. In this talk, the concept and experimental details of chiral SFG spectroscopy will be presented and which hyperpolarizability tensors are involved in our observables will be discussed. We anticipate that this femtosecond OA VSFG technique will be of use in further developing ultrafast time-resolved chiroptical spectroscopy and chiral vibrational microscopy.
E-mail tglee@kbsi.re.kr