First Real-Time Visualization Of Excited-State Aromaticity Driving Molecular Shape Changes

Scientists led by Hikaru Kuramochi at the Institute for Molecular Science/SOKENDAI have successfully visualized, in real time, how excited-state aromaticity emerges within hundreds of femtoseconds and drives a molecule to transition from a bent to a planar structure in a few picoseconds.

Using advanced techniques such as time-resolved impulsive stimulated Raman spectroscopy (TR-ISRS) on a newly synthesized cyclooctatetraene-based “flapping molecule” called TP-FLAP, the team observed the ultrafast structural changes. It confirmed that aromaticity appears before and facilitates the planarization process. This study provides critical insights into nonequilibrium dynamics governed by excited-state aromaticity, offering new avenues for designing photoactive materials like molecular sensors and light-driven switches.

Real-Time Visualization of Excited-State Aromaticity

The research team led by Hikaru Kuramochi successfully visualized excited-state aromaticity in real-time using advanced spectroscopy techniques. By employing femtosecond transient absorption and TR-IR spectroscopy, they could capture the dynamic structural changes of the molecule TP-FLAP with unprecedented temporal resolution.

Upon excitation, TP-FLAP transformed from its bent conformation to a planar structure within picoseconds. This structural change was driven by the emergence of aromaticity in the excited state, which preceded and directed the conformational dynamics. The study demonstrated that aromaticity influences molecular stability and plays a crucial role in driving structural transitions.

The findings underscore the importance of excited-state aromaticity in chemical reactivity and provide new insights into the dynamic behavior of molecules under photochemical conditions. This work opens up possibilities for studying similar systems, offering a deeper understanding of how electronic excitations induce conformational changes.

Broader Impact on Understanding Light-Driven Processes

The research on TP-FLAP investigates how excited-state aromaticity influences its structural dynamics using femtosecond transient absorption and TR-IR spectroscopy. These techniques allow observation of ultrafast electronic transitions and structural changes, respectively. Upon excitation, TP-FLAP transitions from a bent to a planar conformation within picoseconds due to the emergence of aromaticity in the excited state, which stabilizes the molecule.

The study highlights that this transformation is driven by delocalized electrons in the excited state, leading to a more stable, planar structure. This understanding has implications for fields like photosynthesis and photovoltaics, where ultrafast structural dynamics are crucial. The research suggests that excited-state aromaticity not only affects molecular stability but also drives conformational changes, influencing chemical properties and reactions.

The combination of transient absorption and TR-IR spectroscopy provides a comprehensive view by correlating electronic excitation with structural dynamics. This approach advances the understanding of molecular behavior under photochemical conditions and demonstrates the utility of advanced spectroscopic techniques in studying complex dynamic processes. The findings offer insights into how electronic excitations induce conformational changes, potentially applicable to designing materials for solar cells or understanding energy transfer in biological systems.