Developments of novel interface-selective nonlinear spectroscopies and elucidations of molecular mechanisms of interfacial phenomena

Woongmo Sung

Emergences of novel experimental techniques often open new doors for finding new phenomena as well as unknown mechanisms, especially for microscopic elucidations. In our group, by developing new techniques based on the even-order nonlinear optics, we investigate the structures and dynamics of molecules at interfaces. Our studies are opening up a new field of interfacial science.

Research outline

The static and dynamic properties of molecules at interfaces have attracted much attention in a wide range of scientific fields. It is known that interfaces have unique properties that differ substantially from those in bulk materials. However, microscopic mechanisms of such interfacial phenomena are hardly understood even today. Even very simple questions, such as how are the structure and orientation of water molecules at the air/water interface, have not been answered until 10 years ago. Even-order nonlinear spectroscopic methods are the most powerful techniques for the investigation of molecular properties at interfaces. These methods are based on an even-order nonlinear susceptibility χ⁽²ⁿ⁾ (n=1,2,…), which allows us to probe molecules specifically at interfaces where inversion symmetry is necessarily broken. In our group, by developing new techniques based on the even-order nonlinear optics, we investigate the structures and dynamics of molecules at interfaces. These novel techniques allow us to find various kinds of new physical insights associated with interfacial science, opening up a new way to study interfacial science. Recently, we are focusing on three major themes: (1) Ultrafast hydrogen bond dynamics of water at aqueous interfaces. (2) Photochemical reaction dynamics at interfaces. and (3) Structure-function relation at complex interfaces.

Projects

Development of novel interface-selective nonlinear spectroscopies

Interface properties studied by the use of various probe molecules

Hydrogen bonds at model biological interfaces

Hydrogen bond dynamics at the air/water interface

Photochemical reaction dynamics at interfaces

Structure-Function relation of buried solid/liquid interfaces

Further extension of our technique to electrode interfaces and its applications

Members

Subhadip, Yishuai Pan (Visiting scientist), Nihonyanagi, Woongmo, Feng Wei (OB, visiting scientist), Kinoshita; 2024/8/22.

Woongmo Sung (Group leader)

Subhadip Roy

Erika Kinoshita

Selected publications

1. W. SUNG, S. NIHONYANAGI, and T. TAHARA
   Inhomogeneity and Vibrational Coupling of Free OH Stretch at the Air/Water Interface
   J. Am. Chem. Soc. 148, 18074-18079 (2026).
2. W. SUNG, S. NIHONYANAGI, and T. TAHARA
   Development of a Setup for Interferometric Two-dimensional Heterodyne-detected Vibrational Sum-frequency Generation (2D HD-VSFG) Measurements to Study Liquid Interfaces with Sub-100 fs Time Resolution
   J. Chem. Phys. 163, 16204/1-16204/12 (2025).
3. F. WEI, S. NIHONYANAGI, and T. TAHARA
   Elucidation of the pH-dependent electric double layer structure at the positively charged alumina/water interface using heterodyne-detected vibrational sum-frequency generation
   J. Am. Chem. Soc. 147, 22402-22411 (2025).
4. E. KINOSHITA, W. SUNG, S. NIHONYANAGI, H. OKUYAMA, and T. TAHARA
   Frequency-dependent vibrational relaxation time of OH stretch at the air/isotopically diluted water interface
   J. Phys. Chem. Lett. 16, 1088-1094 (2025).
5. S. ROY, M. AHMED, S. NIHONYANAGI, and T. TAHARA
   Time-resolved heterodyne-detected electronic sum frequency generation (TR-HD-ESFG) spectroscopy: A new approach to explore interfacial dynamics
   J. Chem. Phys. 161, 174202/1-174202/9 (2024).
6. W. SUNG, K. INOUE, S. NIHONYANAGI, and T. TAHARA
   Unified Picture of Vibrational Relaxation of OH Stretch at the Air/Water Interface Obtained by Time-Resolved, Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy
   Nat. Commun. 15,  1258 (2024).
7. F. WEI, S. URASHIMA, S. NIHONYANAGI and T. TAHARA
   Elucidation of pH-Dependent Electric Double Layer Structure at the Silica/Water Interface Using Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy
   J. Am. Chem. Soc. 145, 8833-8846 (2023).
8. R. KUSAKA, S. NIHONYANAGI, and T. TAHARA
   The photochemical reaction of phenol becomes ultrafast at the air–water interface
   Nat. Chem. 13, 306 (2021). Front Cover 
9. K. INOUE, M. AHMED, S. NIHONYANAGI, and T. TAHARA
   Reorientation-induced relaxation of free OH at the air/water interface revealed by ultrafast heterodyne-detected nonlinear spectroscopy 
   Nat. Commun. 11, 5344 (2020).
10. S. NIHONYANAGI, S. YAMAGUCHI and T. TAHARA
    Direct evidence for orientational flip-flop of water molecules at charged interfaces: a heterodyne-detected vibrational sum frequency generation study
    J. Chem. Phys. 130, 20, 204704 (2009).