Hannover 2016 – scientific programme

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MO: Fachverband Molekülphysik

MO 20: Femtosecond Spectroscopy 4

MO 20.1: Talk

Friday, March 4, 2016, 11:00–11:15, f102

The primary photochemical processes of a ferracyclobutadiene in liquid solution studied by ultrafast mid-infrared spectroscopy — •Boris Wezisla, Jörg Lindner, and Peter Vöhringer — University of Bonn

Metallacyclobutadienes belong to a class of molecules, which are of particular interest in modern catalysis, since they have been shown to be key intermediates in alkyne metathesis. These reactions are important tools in the synthesis of complex molecules, drugs, and polymers. Our group recently communicated laser flash photolysis experiments combined with time-resolved Fourier-transform infrared spectroscopy of a pseudo-square-pyramidal ferracyclobutadiene (FeCBD). This study focused on the timescale of nanoseconds to milliseconds, and found a primary cleavage of an equatorial carbonyl ligand, which is subsequently replaced by the solvent molecule within the time resolution.

Here, we expand this study by exploring the primary processes leading to the formation of this solvent species after excitation of metal-to-CO CT states with 355 nm or 266 nm laser pulses. The ensuing photochemical processes are detected in a time- and frequency-resolved manner using femtosecond mid-infrared (fs-MIR) spectroscopy in the carbonyl stretching region (1900−2100 cm⁻¹). The spectro-temporal evolution of the transient signal reveals that the primary events are complete within 300 ps. The primary quantum yield for the formation of a FeCBD featuring a solvent molecule in the equatorial binding site is found to be less then 20%. The results are discussed in terms of TD-DFT and extensive modeling of the time-dependent mid-IR response.