Multiconfigurational methods. The multiconfigurational calculations were performed with a state-averaged complete active space self-consistent field (SA-CASSCF) using OpenMolcas 21.02. The methods are described with the format SA(N)-CASSCF(m,n), where N is the number of singlet states the calculation is averaged over. The variables m and n denote the number of electrons and orbitals used in the active space, respectively. For all included molecules, we used a (10,9) active space consisting of two σ and σ* orbitals, two π and π* orbitals, and one lone-pair orbital, including a lone pair on the oxygen atom in the cyclopropenone moiety. The active space is shown in Figure . We used SA(4)-CASSCF(10,9)/ANO-S-VDZP multiconfigurational calculations to optimize the geometries for the ground and excited states and to run minimum energy path (MEP) calculations to track the steepest path along the excited state, starting from the Franck-Condon (FC) point. We used the extended multi-state complete active space perturbation theory (XMS-CASPT2) single-point energy correction to account for dynamic correlation for all multiconfigurational calculations. All optimized structures had their vibrational frequencies computed to confirm that they were stationary points (zero imaginary frequencies).