講演情報
[11p-C213-8]Observation of Conical-Intersection-Mediated Nonadiabatic Ring-Opening Dynamics in Thiophene
〇(D)Zhiyi Zhou1, Satoi Wada2, Yuto Arai1, Kambara Ryuto3, Tetsuya Taketsugu2,4, Taro Sekikawa1 (1.Fac. of Eng., Hokkaido Univ, 2.WPI-ICReDD, Hokkaido Univ, 3.Grad. Sch. of Chem. Sci. Eng., Hokkaido Univ., 4.Fac. of Sci., Hokkaido Univ)
キーワード：
Time-Resolved Photoelectron Spectroscopy、Thiophene、Nonadiabatic Dynamics
Five-membered aromatic heterocycles containing π-conjugated rings are key building blocks in photochemical and optoelectronic systems. Understanding their excited-state reaction dynamics is essential for establishing structure–function relationships governing photoinduced processes. Thiophene represents a prototypical sulfur-containing heterocycle whose excited-state relaxation has been suggested to proceed predominantly via a ring-opening (RO) pathway involving S–C bond cleavage and nonadiabatic transitions mediated by conical intersections (CIs). Despite extensive theoretical investigations, direct experimental observation of the complete RO dynamics remains challenging. Previous ultraviolet (UV)-based time-resolved spectroscopic studies have been limited by the available probe photon energies, restricting observations primarily to low-binding-energy features associated with low-lying excited states and outer-valence molecular orbitals (MOs). This limited spectral window hinders access to deeper MOs that are highly sensitive to bond rearrangement, thereby obscuring direct observation of CI-mediated relaxation dynamics.
In this work, we employ extreme ultraviolet (EUV)-based time-resolved photoelectron spectroscopy (TRPES) to investigate the ultrafast nonadiabatic dynamics of thiophene over an extended photoelectron energy range. The broad spectral coverage enables direct monitoring of electronic redistribution accompanying structural evolution following excitation to the S2 (ππ*) state. The measurements reveal initial photoexcitation, ultrafast internal conversion, subsequent ballistic nuclear wavepacket evolution, passage through CI accompanied with chemical bond broken, and further isomerization. These results provide direct experimental insight into the CI-mediated RO mechanism of thiophene and demonstrate the capability of EUV-TRPES to simultaneously probe coupled electronic and nuclear dynamics in complex photochemical reactions.
In this work, we employ extreme ultraviolet (EUV)-based time-resolved photoelectron spectroscopy (TRPES) to investigate the ultrafast nonadiabatic dynamics of thiophene over an extended photoelectron energy range. The broad spectral coverage enables direct monitoring of electronic redistribution accompanying structural evolution following excitation to the S2 (ππ*) state. The measurements reveal initial photoexcitation, ultrafast internal conversion, subsequent ballistic nuclear wavepacket evolution, passage through CI accompanied with chemical bond broken, and further isomerization. These results provide direct experimental insight into the CI-mediated RO mechanism of thiophene and demonstrate the capability of EUV-TRPES to simultaneously probe coupled electronic and nuclear dynamics in complex photochemical reactions.