The molecule 2,3-diphenyl-2-norbornene (2,3-diphenylbicyclo[2.2.1]hept-2-ene) (1) has been prepared as a model for cis-stilbene (2) in which single-bond but not double-bond torsion (within the π system) is sterically possible on both the ground-state and lowest triplet-state surfaces. A comparison of the crystal structure of (1) with previously published data for a derivative of (2) shows that the non-planar π-system geometries of (1) and (2) are indeed similar. This has allowed definitive conclusions to be drawn concerning the phenomenon of «nonvertical» triplet-energy transfer