Time-resolved spectroscopy monitors the electronic state of matter as a function of time. Particularly, an optical pulse shorter than vibrational period (> 10 fs) has a capability of investigating vibrational and electronic dynamics simultaneously. Since the reactant and product should show different electronic properties and vibrational dynamics, analyzing such spectral response enables us to reveal the detailed mechanism of photochemical and photophysical processes.

We reveal the reaction dynamics of photochemical reactions (e.g., proton transfer, charge transfer, and isomerization) and photophysical processes (e.g., internal conversion, intersystem crossing, and photosynthetic energy transfer) using femtosecond multidimensional spectroscopy.

References

[1] J. Phys. Chem. Lett. 2020, 11 (3), 755-761
[2] J. Phys. Chem. Lett. 2021, 12 (27), 6292-6298
[3] J. Phys. Chen. Lett. 2022, 13 (4), 1099-1106

Transition lines of material in condensed phase (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] Chem. Rev. 2022, 122 (3), 4257-4321
[2] J. Phys. Chem. Lett. 2021, 11 (8), 2864-2869
[3] Nat. Commun. 2021, 11 (1), 1-10

Development of time-resolved spectroscopy and multidimensional spectroscopy using single photons.

References

[1] J. Phys. Chem. Lett. 2024, 15, 5407-5412

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.