Hammershøj et al. describes the synthesis and basic characterization of phenyl bromide functionalized norbornadienes designed to study the photo induced 2+2 cycloadition reaction known to happen in these systems. The report is well written and the experimental details comprehensive. In light of the motivation of the work - the use in time resolved pump-probe measurements quantum yield measurements as well as the thermal reversal reaction at different temperatures might reveal important parameters, such as the quantum yield of reaction and activation energy for the conversion from quadricyclane to norbornadiene, see e.g. Gray et al. Chem. Commun. 2014, 50 (40), 5330 - 5332. I am very curious to see what the time resolved measurements will bring in terms of details of the mechanism and the structures of the transition states. For a recent high level computational study, one could refer to: Ivana Antol, Journal of Computational Chemistry 2013, 34, 1439–1445.