Mainz 2026 – scientific programme

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MO: Fachverband Molekülphysik

MO 4a: Ultrafast Structural Dynamics II

MO 4a.2: Talk

Monday, March 2, 2026, 17:15–17:30, P 110

Liquid-Phase MeV Ultrafast Electron Diffraction Captures the Twisted Intramolecular Charge Transfer Ultrafast Dynamics in DMABN/DMSO — •Simone Stahl¹, Sudhir Kumar¹, Joanne Woodhouse¹, Athira Mini Santhosh¹, Bo Huang², Keke Chen², Longteng Yun², Chuyuan Zhai², Benjamin Fingerhut³, Renkai Li², Jie Yang², and Kasra Amini¹ — ¹Max-Born-Institut, Max-Born-Str. 2A, 12489 Berlin, Germany — ²Center of Basic Molecular Science, Department of Chemistry, Tsinghua University, Beijing 100084, China — ³Department of Chemistry and Centre for NanoScience, Ludwig-Maximilians-Universität München, 81377, München, Germany

4-(N,N-dimethylamino)benzonitrile (DMABN) is a prototypical donor-acceptor molecule exhibiting anomalous dual fluorescence in polar solvents commonly attributed to photoinduced twisted intramolecular charge transfer (TICT) [1,2]. Despite decades of spectroscopic studies, direct structural evidence of TICT formation in solution has been lacking. Here, we report the first liquid-phase MeV ultrafast electron diffraction measurement of DMABN in high polar dimethyl sulfoxide. With ∼100 fs resolution, we directly resolve the delayed onset of large-amplitude dimethylamino torsion revealing a distinct TICT structural signature emerging at ∼550 fs and maturing within ∼900 fs after excitation.

[1] Z. R. Grabowski et al., Chem. Rev. 103 3899 (2003).

[2] M. A. Kochman et al., J. Phys. Chem. A 125 8635 (2021).

Keywords: Coupled electronic-nuclear dynamics; ultrafast electron diffraction; femtochemistry; liquid-phase photochemistry