The transition from fossil fuels to renewable energy sources requires technologies that are capable of both producing and storing energy. Attractive candidates that combine these two features are molecular photoswitches used for molecular solar thermal (MOST) energy storage. One of the most promising MOST systems is the norbornadiene/quadricyclane (NBD/QC) couple. We present the first density functional theory benchmark study of a NBD/QC derivative in vacuum with respect to novel gas-phase experiments. It was found that the M06-2X/def2-TZVP and M06-2X/6-311+G(d) level of theories produced the most accurate results with respect to the maximum absorption wavelength and the energy density.