Bonn 2025 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 5: Ultrafast Dynamics I

MO 5.2: Vortrag

Dienstag, 11. März 2025, 11:15–11:30, HS XVI

Excited-state wavepacket dynamics of the photoredox catalyst Ti^IV(Cp)2(NCS)2 — •Jonas Schmidt, Luis Ignacio Domenianni, and Peter Vöhringer — Clausius-Institut für Physikalische und Theoretische Chemie, Bonn, Deutschland

Recently, we reported the observation of the entry events of Ti(Cp)2(NCS)2 into a photo-catalytic cycle in real-time. Using time-resolved mid-infrared spectroscopy, we identified the intermediate states involved and tracked the reductive quenching reaction of the active catalyst with a sacrificial amine electron donor over broad timescales, spanning from picoseconds to hundreds of microseconds.

Here, we report on the very early dynamics of the electronic relaxation of the locally excited singlet state, S3. To this end, we employed ultra-fast near-UV-pump/white-light-probe spectroscopy with a time resolution of a few tens of femtoseconds. We could observe a prompt, structureless transient absorption ranging from 600 to 900 nm. On timescales below two picoseconds, the absorption exhibits coherent oscillations with a frequency of 140 cm^-1. An analysis of probe-wavelength dependence of their phase and amplitude provides evidence that they are due to vibrational wavepacket dynamics in the energetically lowest singlet excited state, S1, of the complex. TDDFT suggests that the initial S3-to-S1 internal conversion creates a coherent superposition in the Cp-Ti-Cp bending vibration of S1.

We are currently in the process of conducting complementary experiments on the fully methylated complex Ti(Cp)*2(NCS)2 to verify this assignment.

Keywords: ultra-fast spectroscopy; wave-packet dynamics; photo-redox catalysis; transition-metal photochemistry