Ultrafast structural dynamics in various π-conjugated molecular systems probed by time-resolved electronic and vibrational spectroscopy

• Main Author: Kim, Dongho
• Other Authors: Asian Spectroscopy Conference 2020
• Format: Conference or Workshop Item
• Language: English
• Published: 2020
• Subjects: Science::Chemistry; Femtosecond Broadband Fluorescence Upconversion Spectroscopy; Femtosecond Infrared Spectroscopy
• Online Access: https://hdl.handle.net/10356/144280
• Institution: Nanyang Technological University

Aromaticity, the special energetic stability derived from cyclic [4n+2]π-conjugation, has been the topic of intense interest in chemistry. Recently, the pioneering work by Colin Baird on aromaticity reversal, postulating that aromatic (antiaromatic) character in the ground state reverses to antiaromatic (aromatic) character in the lowest excited triplet state, has attracted much attention. The completely reversed aromaticity in the excited states provides direct insight into understanding the properties of photoactive materials. However, most studies on excited state aromaticity have been based on the theoretical point of view. Time-resolved optical spectroscopies can provide a new and alternative avenue to experimentally evaluate excited state aromaticity. With monitoring ultrafast changes in the excited states, they can provide valuable information for excited state aromaticity. In this regard, recent breakthroughs in experimentally assessing aromaticity reversal in the excited states with time-resolved optical spectroscopic measurements are introduced. Time-resolved electronic and vibrational absorption spectroscopies capture the change of electronic structure and molecular conformations driven by the change of aromaticity and provide clear evidence for aromaticity reversal in the excited states. These approaches will pave a way for the development of new experimental indices for the evaluation of excited state aromaticity and its applications.