Photophysics and photochemistry of a d5 Ruthenium complex

Transition metal complexes (TMCs) with charge transfer states play a crucial role in photophysical and photochemical processes, particularly in energy conversion applications. This thesis investigates the photophysics and photochemistry of the d⁵ ruthenium complex ([Ru(III)(phtmeimb)2]+), focusing on its excited-state dynamics and charge transfer properties. The photophysical study involves steady-state absorption and emission spectroscopy, as well as temperature-dependent measurements, to characterize the electronic transitions and relaxation pathways the complex. The impact of oxidation state on photophysical properties is examined using cyclic voltammetry and UV-Vis spectroelectrochemistry. Time-resolved transient absorption and emission spectroscopy are the core of this thesis. These techniques were employed to explore the excited-state evolution. This study reveals the key role of internal conversion on the excited-state relaxation of ([Ru(III)(phtmeimb)2]+). Temperature-dependent emission studies reveal a nearly barrier-less character of the excited state depopulation. At the temperatures close to glass transition of solvent, we identified the presence of a weak thermally activated contribution to the non-radiative pathways, which is most probably related to restrictions imposed by solidification of the solvent on intra-molecular degrees of freedom related to the efficiency of internal conversion. By transient absorption, we observed a clear dependence of the excited state energy relaxation dynamics on the nature of the initially populated excited state. We also propose a weak influence of solvation dynamics in highly polar solvent on evolution of the excited state despite of a distinct charge transfer character of the employed excitations.In the photochemical investigation, intermolecular charge transfer is studied by introducing an electron donor N,N-dimethylaniline (DMA). The charge separation (CS) and charge recombination (CR) dynamics were analyzed across a wide range of DMA concentrations to reveal a strong dependence of CS and CR on DMA concentration, with indication of long-live signal at high concentrations. By a comparative analysis of CS and CR dynamics in ([Ru(III)(phtmeimb)2]+) with the previously studied ([Fe(III)(phtmeimb)2]+) we conclude that CS happens in the normal region whereas CR in inverted region of Marcus parabola.These results provide an understanding of d⁵ LMCT complex excited-state behavior and their potential for light-driven catalysis and energy conversion applications.