Ultrafast Ion Spectroscopy of Transition Metal Complexes in Gas Phase

This dissertation investigates the ultrafast photophysics and photochemistry of transition metal (TM) complexes in the gas phase using ion-trap mass spectrometry combined with femtosecond and nanosecond laser spectroscopy. TM complexes are widely utilized in photocatalysis, energy conversion, and molecular electronics, where their excited-state dynamics dictate their efficiency and functionality. However, studying these dynamics in solution often introduces complications due to solvent interactions and counterion effects. By isolating the complexes in the gas phase, this work eliminates these external influences, providing direct insights into fundamental photochemical processes such as metal-to-ligand charge transfer (MLCT), intersystem crossing (ISC), and ligand dissociation. The experimental approach is based on an electrospray ionization quadrupole ion trap mass spectrometer (ESI-QIT-MS), where molecular ions are trapped before being selectively excited with tunable ultrafast laser pulses. The resulting fragmentation pathways, photo-induced dissociation (PD) spectra, and kinetic relaxation dynamics are recorded, allowing for precise characterization of excited-state behavior. This method provides a unique way to explore the electronic relaxation and reactivity of TM complexes in an environment free of solvent effects. Key research topics covered in this dissertation include: • Ultrafast dynamics of Ru(II) polypyridyl complexes, including MLCT relaxation and ligand dissociation mechanisms. • Impact of systematic ligand modifications on excited-state lifetimes and photodissociation efficiency. • Bimetallic Au(I)/Ru(II) cyclophanyl complexes, probing cooperative metal-metal interactions in photoredox processes. • Cu(I) complexes, investigating their metal-centered excited states relevant to photocatalysis. • Gas-phase ion spectroscopy of polyoxovanadates, serving as molecular models for heterogeneous vanadium catalysis. • Charge-transfer dynamics in heterobimetallic Ru-Rh complexes, focusing on photoinitiated bond activation. By leveraging gas-phase ultrafast spectroscopy within an ion trap mass spectrometer, this work establishes a novel approach to studying TM photochemistry, providing high-resolution kinetic and spectroscopic data independent of solvation effects. These insights contribute to the fundamental understanding of TM complexes and aid in the rational design of future photocatalysts and optoelectronic materials.