Intramolecular processes of deactivation of 1,3-dimethyl-4-thiouracil (DMTU) from the second excited singlet (S₂) (π, π*) and the lowest excited triplet (T₁) (π, π*) states have been studied using perfluoro-1,3-dimethylcyclohexane (PFDMCH) as a solvent. The spectral and photophysical (PP) properties of DMTU in CCl₄, hexane and water have also been described. For the first time, the fluorescence from S₂ state DMTU has been observed. The picosecond lifetime of DMTU in the S₂ state (τ_S2) in PFDMCH has been proposed to be determined by a very fast intramolecular reversible process of hydrogen abstraction from the ortho methyl group by the thiocarbonyl group. The shortening of τ_S2 in CCl₄ is interpreted to be caused by the intermolecular interactions between DMTU (S₂) and the solvent. Results of the phosphorescence decay as a function of DMTU concentration were analyzed using the Stern–Volmer formalism, which enabled determination of the intrinsic lifetime of the T₁ state ( ) and rate constants of self-quenching (k_sq). The lifetimes, , of DMTU in PFDMCH and CCl₄ are much longer than the values hitherto obtained in more reactive solvents. The PP properties of DMTU both in the S₂ and T₁ states have been shown to be determined by the thiocarbonyl group.