Transition lines of material in condensed phases (e.g., solid, liquid, and solution) are structureless due to the complexity of the system itself or its environment. Thus, it is difficult to fully understand the condensed-phase phenomena by linear spectroscopy. Nonlinear spectroscopy has a capability of spreading congested spectral responses on multidimensional space, so that the spectral response of interest (e.g., reaction dynamics) can be selectively examined. Here, the femtosecond laser is an appropriate light source for demonstrating multidimensional spectroscopy since it provides high peak power, high time resolution, and wide spectral window.

We develop the new multidimensional spectroscopy techniques both experimentally and theoretically to study reaction mechanisms that have not been clarified.

References

[1] J. Chem. Phys. 2025, 163, 164307
[2] Chem. Rev. 2022, 122 (3), 4257-4321

Time-resolved spectroscopic techniques, such as transient absorption and time-resolved fluorescence spectroscopy, have long been established and remain essential tools for probing ultrafast dynamics in molecular systems. Conventional time-resolved spectroscopy is typically described within a semiclassical framework of light–matter interaction; however, certain properties of matter cannot be fully understood within this approach alone. Fully quantum-mechanical light–matter interactions enable unprecedented nonlinear spectroscopic methods by exploiting uniquely quantum properties of light sources, including entanglement and photon statistics, which are inaccessible to classical light. 

References

[1] Sci. Adv. 2025, 11, eadw9759
[2] J. Phys. Chem. Lett. 2024, 15 (20), 5407-5412

Molecules in condensed phases exhibit strong intermolecular interactions, making it difficult to extract detailed structural and dynamical information using conventional linear spectroscopy. Although time-resolved spectroscopy has been developed to probe photoinduced dynamics, the resulting kinetic information alone does not fully capture the underlying quantum dynamics. Our research focuses on elucidating quantum dynamical processes, such as proton transfer and photosynthetic energy transfer, where quantum effects play a crucial role, by employing coherent vibrational spectroscopy beyond conventional time-resolved spectroscopic approaches. 

References

[1] J. Phys. Chen. Lett. 2026, 17 (19), 5424-5431
[2] J. Phys. Chen. Lett. 2022, 13 (4), 1099-1106

Light can change the electronic state of a material by interacting with its transition dipole moment. Weak light-matter interaction results in electronic transition, while strong light-matter interaction modulates the electronic wave function itself. Based on that, it is possible to control chemical reactions optically by employing the weak or strong light-matter interaction.

We control chemical reactions within weak and strong light-matter interaction regimes based on the reaction dynamics revealed by femtosecond experiment. In weak coupling regime, highly reactive states are populated by shaping optical pulses. In strong coupling regime, molecular electronic wave functions are modulated using molecular cavity to control the chemical reactivity.