Early-time photodynamics of ruthenium-based photocatalysts for light-induced hydrogen generation

Abstract

This thesis aims to provide a fundamental understanding of the early-time photodynamics of a series of Ru/M (M = Pd or Pt) bimetallic photocatalysts for light-induced hydrogen generation. This class of complexes adopts a general structure involving a Ru(II) center coordinated to two peripheral ligands and one bridging ligand, which bonds to a catalytic metal center as schematically shown in Figure 1. Photoexcitation of the complexes leads to intra-molecular electron transfer processes, which are investigated by using ultrafast time-resolved spectroscopic techniques. The excited state photodynamics are systematically studied considering the individual building blocks of the complexes (i.e. peripheral/bridging ligands and the catalytic moiety). The knowledge obtained in this thesis facilitates interpreting the structure-reactivity relationship, allowing the photophysical exploration of other analogous complexes, and guiding the optimization of new photocatalysts with improved photocatalytic efficiency. This thesis is organized in the following way: •Chapter 1 provides a general background of photocatalytic hydrogen generation, coordination complexes, and time-resolved spectroscopy. In particular, the prototype complex [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) is introduced in detail to provide key concepts which are frequently referred to in later chapters. •Chapter 2 discusses the methodological aspects of transient absorption, which is the main technique used in this thesis. •Chapter 3 explores the impact of the bridging ligand on the excited state properties of two analogous Ru/Pd complexes. •Chapter 4 investigates the critical role played by the catalytic moiety in the early-time photodynamics of two analogous Ru/Pd and Ru/Pt complexes. •Chapter 5 studies the influence of the peripheral ligands on the photodynamics for a series of Ru/Pt complexes. •Chapter 6 focuses on the photodynamics of a new Ru/Pt complex whose design is based on the knowledge obtained in previous chapters. •Chapter 7 extends the discussion of Chapter 4 by applying time-resolved X-ray absorption spectroscopy to investigate the catalytic Pt center of a Ru/Pt complex. •Chapter 8 summarizes the main conclusions obtained from the previous chapters, and presents an outlook overview.