Characterizing Ultrafast Intersystem Crossing Pathways in Molecular Pt Dimers Using Time-Resolved Wide-Angle X-ray...

Area of Science:

• Photochemistry and Photophysics
• Inorganic Chemistry
• Materials Science

Background:

• Vibronic coupling is a key mechanism influencing charge transfer states and intersystem crossing (ISC) rates in transition metal complexes.
• Previous studies have observed vibronic coupling-driven ISC in platinum(II) dimer complexes, where Pt-Pt stretching vibrations tune excited-state pathways.

Purpose of the Study:

• To investigate the role of vibronic coupling in enhancing intersystem crossing (ISC) rates in platinum(II) dimer complexes.
• To quantify the Pt-Pt bond contraction and coherent vibrational wavepackets (CVWPs) dynamics following MMLCT excitation.
• To elucidate the influence of different bridging ligands on the ISC mechanism via ultrafast TR-WAXS analysis.

Main Methods:

• Time-resolved wide-angle X-ray scattering (TR-WAXS) was employed to probe ultrafast structural dynamics.
• TR-WAXS was used to measure Pt-Pt distance changes and analyze coherent vibrational wavepackets (CVWPs) in Pt dimers.
• Analysis of interference patterns between CVWPs was performed to track excited-state trajectories.

Main Results:

• Both Pt dimer complexes exhibited Pt-Pt bond formation (contraction of ~0.25 Å) and encoded CVWPs upon MMLCT excitation.
• The time-dependent evolution of CVWPs differed between the two complexes, indicating ligand-dependent dynamics.
• Interference patterns in CVWPs provided indirect information about electronic excited-states and the ISC mechanism.

Conclusions:

• The study demonstrates that vibronic coupling plays a crucial role in the ISC mechanism of Pt(II) dimers.
• Ultrafast TR-WAXS is a powerful tool for revealing excited-state dynamics and ligand effects on ISC.
• The interference of CVWPs offers insights into the bridge-dependent nature of ISC in these systems.