Photochemistry is an effective means by which strained, energy-dense compounds can be accessed while facilitating green chemistry through mild reaction conditions. Gas-evolving reactions produce gases such as oxygen or carbon dioxide (CO 2 ) and are utilized for processes such as the oxygen reduction reaction (ORR) and CO 2 reduction. Photochemical decarbonylation has been utilized to promote cross-coupling and form biaryl compounds , promote synthetic pathways towards strained compounds such as tetrahedrane , and facilitate transition-metalcatalyzed C-C bond cleavage. Small concentrations of CO have been shown to have therapeutic effects, including it being used as an anti-inflammatory agent, and used to treat cancer and bacterial infections. CO delivery can be light-activated with a photoactive CO-releasing molecule (CORM). Light enables spatiotemporal activation of different chemical processes, including energy storage in materials chemistry and pro-drugs in drug delivery . Strained cycloaddends (e.g., cyclooctynes and 1,3-dipoles) can be accessed using light through a class of biorthogonal reactions known as 'photoclick chemistry.' Photoclick reactions involve two phases: 1) light-promoted activation of the desired reactive species and 2) a facile thermal strain-promoted cycloaddition reaction in the biochemical milieu. Strain-promoted cycloadditions can occur without Cu(I) catalysts and benefit from high reaction rates. The first photoclick reaction was reported by Lin and co-workers in 2008 and involved the tetrazole-ene cycloaddition reaction. Upon irradiation, N 2 is photochemically extruded from tetrazole and the remaining 1,3-dipole, nitrile imine can undergo reactions with 2𝜋-cycloaddends. Other photoclick reactions include a wide variety of processes, including photoprotected cyclooctynes, syndones, azirines, Diels Alder reactions, and thiol click reactions. Functionalizing the vinyl positions of 1 with aryl groups redshifts the absorption wavelength to activate decarbonylation (λ = 350 nm). The quantum yield of 4-dibenzocyclooctynol after irradiation with 350 nm light was measured to be 0.33 by Popik and co-workers. The effects of different substituents on both cyclopropenone and cyclooctynol were also reported by Popik and co-workers, who used multi-photon absorption with a near-IR laser to generate reactive intermediates to undergo a SPAAC reaction. Recently, Kunishima and co-workers have used a visible-light responsive photocatalyst to redshift the absorption wavelength required for the decarbonylation of substituted cyclopropenones. While the thermal cycloadditions involved in bio-orthogonal chemistry have been intensely researched by experimentalists and theorists, the photochemical steps of the reactions have received less attention. We suspect this is due to the challenge of experimentally studying molecular excited states and reactive intermediates in the typically ultrafast timescale of photochemical reactions (10 -13 to 10 -8 seconds). Computational approaches provide valuable structural information on a 1-10 picosecond timescale. Fang and co-workers investigated the photochemical decarbonylation of 2 in 2014 using gas phase multiconfigurational calculations (CASSCF and MS-CASPT2) to locate minima and conical intersections on the S 0 and S 1 potential energy surfaces (PESs). Ab initio multiple spawning (AIMS) non-adiabatic molecular dynamic simulations were performed to investigate the photochemical reaction dynamics along the S 1 surface. The authors located one S 1 /S 0 conical intersection, leading to the dissociation mechanism in 72% of trajectories. The authors also located a second S 1 /S 0 conical intersection that reverts to the reactant (cyclopropenone) in 93% of trajectories. Fang reports an S 1 lifetime of 125 fs for 2. We now use NAMD simulations with multiconfigurational quantum chemical calculations to understand the photochemical reaction mechanisms of 1 and 2 in a gaseous and aqueous environment to understand the role of chromophore-solvent interactions. Our analysis is especially focused on the role of the electronic structure of the ground state pseudo-aromaticities and the S 1 pseudo anti-aromaticities of these cyclopropenones. Scheme 2 illustrates resonance structures corresponding to ground-state (S 0 ) and excited state (S 1 ) aromatic electronic structures. Scheme 2. Resonance structures of cyclopropenone's pseudo aromatic electronic structures in the S 0 -and S 1 -state.