Ultrafast Twisting Dynamics of Thioflavin-T: Spectroscopy of the Twisted Intramolecular Charge-Transfer State

Understanding the excited-state properties of thioflavin-T (ThT) has been of immense importance, because of its efficient amyloid-sensing ability related to neurodegenerative disorders. The excited-state dynamics of ThT is studied by using sub-picoand nanosecond time-resolved transient absorption techniques as well as density functional theory (DFT)/time-dependent DFT calculations. Barrierless twisting around the central C-C bond between two aromatic moieties is the dominant process that contributes to the ultrafast dynamics of the S-1 state. The spectroscopic properties of the intramolecular charge-transfer state are characterized for the first time. The energetics of the S-0 and S-1 states has also been correlated with the experimentally observed spectroscopic parameters and structural dynamics. A longer-lived transient state populated with a very low yield has been characterized as the triplet state.