Abstract Pigment Yellow 101 (PY101) exhibits a rich photochemistry in its S1 state as it undergoes excited state intramolecular proton transfer and trans–cis isomerizations upon photoexcitation. Relaxed scans of its potential energy surface are thus computed along the reaction paths connecting the six most stable conformers using time-dependent density functional theory. The influence of solvation onto the energetics is estimated. PY101 has been chosen, since its photochemistry is not dominated by non-adiabatic effects but can be interpreted like hot ground state chemistry, such that a kinetic rate model may be applicable for its simulation. For the latter an adapted rate model taking the dissipation of the initial excess energy into account has been used, and the obtained results for the excited state processes are in good agreement with available time-resolved experimental data.