RESEARCH

Using pump–probe spectroscopy, time-resolved Raman spectroscopy, and coherent multidimensional spectroscopy, we aim to track changes in molecular electronic states and structures during chemical reactions in real time with ultimate temporal resolution. Through these measurements, we seek to uncover the essential conditions that govern chemical reactions and functional processes in complex molecular systems. In particular, we exploit coherent molecular vibrations induced by ultrashort laser pulses as sensitive probes of molecular dynamics, with the goal of establishing new pictures of photochemical and photophysical processes that go beyond conventional understanding. Our current research focuses on the primary photochemical processes of photoresponsive proteins , as well as exciton dynamics in materials for photoelectric energy conversion.

At room temperature and in solution, molecular environments and structures undergo continuous thermal fluctuations, which can strongly influence the properties and reactivity of individual molecules. Revealing the intrinsic reactivity of individual molecules as shaped by such fluctuating states, and uncovering the origin of this molecular heterogeneity, is essential for understanding the reaction mechanisms of complex molecular systems, including proteins. Conventional spectroscopic methods, however, provide only an ensemble-averaged picture obtained from many molecules. We are developing innovative methodologies that combine ultrafast spectroscopy with single-molecule spectroscopy, with the aim of directly observing reaction dynamics that reflect the individuality of each molecule, as well as how these dynamics evolve and fluctuate over time.

The local environment surrounding a molecule, including its properties and dynamics, is closely related to fluctuations in the molecule’s energy. In amorphous solids, the local environment of each molecule varies in space and time, but such heterogeneity is averaged out in ensemble measurements. By contrast, single-molecule observations reveal distinct molecular behavior in response to subtle differences in local environments.　

By tracking such behavior with nanometer-scale precision, we are developing approaches to image and characterize the nanoscale structure of materials beyond the diffraction limit. Ultimately, we aim to establish methodologies and concepts that connect single-molecule behavior with the macroscopic properties of materials and molecular assemblies.