Investigating the light induced dynamics of a phototoxic Ru (II) based photosensitizer TLD1433 in biologically relevant environments This thesis reports on the photophysical properties of a Ruthenium based photosensitizer (PS) TLD1433 which is currently under human clinical trial for the treatment of non muscle invasive bladder cancer with Photodynamic Therapy (PDT) in biologically relevant environments. The excited state landscape which governs the reactivity and therefore the functionality of the PS is thoroughly investigated with time resolved spectroscopic techniques such as transient absorption and emission spectroscopy in conjunction with steady state spectroscopic techniques such as absorption emission and resonance Raman spectroscopy. The findings recorded in this thesis coherently show that the biological environment alters the photophysical properties of the PS. In general the findings emphasizes on the need to correlate the functionality of PSs used in relation to PDT to their photophysics in environments which can serve as model systems rather than in homogeneous solutions.