To evaluate the solvent effects of water on the photochemical decarbonylation reaction of 1 and 2, we performed 250 fs NAMD simulations beginning from the S 1 -Franck Condon point. Initial conditions were sampled in line with the excellent report by Gonzalez and co-workers this year. We observed an increased quantum yield for the decarbonylation reaction for both systems compared to the gas-phase simulations (58% for 1 and 2). We performed 250 fs NAMD simulations on solvated spheres (20 water molecules) of 1 and 2, starting with initial conditions sampled using MD simulations in CP2K. The NAMD simulations utilized the FSSH surface hopping algorithm and were propagated from the S 1 state. The 𝜎 CC bond lengths in the cyclopropenone ring were measured throughout the trajectories and are represented in Figure . The S 1 /S 0 crossing seams for the solvated systems of 1 and 2 are given by the black dots. The distribution of S 1 /S 0 hopping points for 1 and 2 have a large range of 𝜎 CC bond distances (1.42-3.25 Å). For 1, there were 276 initial conditions submitted from the S 1 after the sampling with MD simulations. Of these 276, 253 crossed to the S 0 by the end of the simulation. Of these 253, there were 19 trajectories where the endpoint was an intermediate structure (one broken 𝜎 CC in the cyclopropenone ring). These intermediate structures were not counted in the final quantum yield. An example intermediate structure is provided in the SI. Of the remaining 234 trajectories, we observed 135 trajectories that underwent decarbonylation (Φ comp = 58%) and 99 that reformed the reactant (42%). For the solvated system of 2, we ran simulations on 481 initial conditions. Of these 481, 20 trajectories (4%) ended at an intermediate structure with a broken 𝜎 CC bond in the cyclopropenone ring. 277 trajectories underwent decarbonylation (Φ comp = 58%), and 173 trajectories (36%) reformed the reactant. We also calculated the ratio of trajectories for 1 and 2 that crossed through the asynchronous (one 𝜎 CC bond of 1.80 Å or longer) and FC-regions (both 𝜎 CC bonds less than 1.80 Å) of the S 1 /S 0 crossing seam. For the solvated system of 1, 237 trajectories (94%) went through a hopping point in the asynchronous region, while 16 (6%) crossed at a hopping point in the FC-region. There were 114 trajectories from the asynchronous hopping region that dissociated (48%) and 88 trajectories that reformed the reactant (37%). From the FCregion of the solvated system of 1, 9 trajectories formed the decarbonylation product (56%), and 4 reformed the reactant (25%). For the solvated system of 2, there were 337 trajectories (70%) that crossed through hopping points in the asynchronous region (one 𝜎 CC bond of 1.80 Å or longer), while 144 trajectories (30%) crossed through hopping points in the FC-region. From the asynchronous region, 198 trajectories (59%) went on to form the products, whereas 116 (34%) reformed the reactant structure. The 20 trajectories with intermediate structures (6%) exclusively went through hopping points in the asynchronous region. From the FC region, there were 78 (54%) trajectories that dissociated and 57 (40%) which reformed the reactant. The hopping point structures from each region of the hopping seam resemble those from the gas phase simulations; the asynchronous hopping points feature a broken 𝜎 CC bond in the cyclopropenone ring, whereas the FC region contains points where both bonds are still intact. The inclusion of an explicit solvent in our NAMD simulations resulted in a 5% and 30% increase in quantum yield for the decarbonylation products of 1 and 2, respectively. This increased yield can be explained by the ratio of trajectories going through the asynchronous and FC regions of the S 1 /S 0 seam. For the solvated NAMD simulations of 1, nearly all trajectories crossed to the S 0 in the asynchronous region (94%), corresponding to a 12% increase compared to the gas-phase simulations. While the decarbonylation yield from the asynchronous region is smaller than for the gas-phase simulations (48% and 64%, respectively), the overwhelming preference for the asynchronous region ultimately leads to a higher quantum yield. From the FC-region of 1, there was a larger number of trajectories (9) that dissociated than those that reformed the reactant (4), which was significantly different than the gas phase. We observed a similar trend along the seam for the solvated system of 2. The number of trajectories hopping in the asynchronous region was increased (70% and 52% for the solvated and gas-phase systems, respectively). While the quantum yield from the asynchronous region was slightly smaller for the solvated system compared to the gas phase (59% and 63%, respectively), the higher ratio of trajectories crossing through this region leads to a higher Φ comp . To understand the solvent effect on the quantum yields for the photochemical decarbonylation pathways of 1 and 2, we evaluated the effects of hydrogen bonding on the initial conditions, the mechanistic pathways, and the nature of the hopping seams.