Mainz 2026 – scientific programme

Parts | Days | Selection | Search | Updates | Downloads | Help

MO: Fachverband Molekülphysik

MO 1: Ultrafast Structural Dynamics

MO 1.2: Talk

Monday, March 2, 2026, 12:00–12:15, P 105

Influence of the Bridging Length on the Ultrafast Isomerization Dynamics of Bridged Azobenzenes in a Molecular Beam — •Pascal Pessier^1,2, Maria Hergert¹, Lukas Guhl¹, and Friedrich Temps¹ — ¹Institute of Physical Chemistry, Christian-Albrechts-University Kiel, Olshausenstraße 40, 24098 Kiel, Germany — ²now at Institute of Physics, University of Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, Germany

Bridged azobenzenes have drawn considerable attention in the last decade due to their superior photochemical properties compared to conventional azobenzene (AB). Here, the ultrafast isomerization dynamics of two bridged azobenzenes, -C₂H₂-bridged diazocine (Dz) and -CH₂-bridged diazepine (Dzp), were investigated using time-resolved time-of-flight mass spectrometry, photoelectron imaging and photoionization-photofragmentation spectroscopy aided by quantum chemical calculations.

While Dz was found to isomerize in a concerted fashion (τ₁ < 38 ± 1 fs), Dzp unfolds first and consecutively isomerizes (τ₁ < 38 ± 7 fs, τ₂ = 680 ± 96 fs), linked to the increased ring strain by the shorter bridge. Further, the ultrafast unfolding motion (τ₁) enables additional adiabatic transitions close to the D₀ minimum with an unfolded structure rather than the FC region in the single-color photoelectron spectra. In the freshly prepared ion, this induced unfolding motion is then conserved as a highly excited butterfly vibration, observable as pronounced oscillation of parent ion yield.

Keywords: molecular photoswitches; azobenzene; time-resolved mass spectrometry; photoelectron imaging spectroscopy; photoionization-photofragmentation