This work presents the results of wavelength dependent Time-Resolved Photoelectron Spectroscopy (TR-PES) and Ion Yield (TR-IY) studies of 2-thiouracil, which can potentially lead to a better understanding of the phototherapeutic effects of thiouracil-based drugs used in medical applications, like cancer treatment. The experiments provide more information about the relaxation dynamics of the molecule, especially its intersystem crossing pathways and high yield of long-lived triplet states that determines the effectiveness of drugs. The results provide evidence of UV excitation to the S₂(¹ππ*) state with ultrafast (<100fs) internal conversion to the S₁(¹nπ*) state and highly efficient intersystem crossing to the ³ππ* state, in hundreds of femtoseconds. Finally, relaxation to the ground state takes place in the hundreds of picosecond timescale. A trend is observed where excitation to higher vibrational levels of the S₂(ππ*) states results in overall faster dynamics through conical intersections that are accessed by out-of-plane distortion of the molecular ring.

INDEX WORDS: 2-Thiouracil, Excited states, Time-resolved, Photoelectron spectroscopy, Relaxation dynamics