Norbornadiene (N) is used as an isolated guest in a host (the crystalline phase of robust syndiotactic polystyrene polymer films) and its valence photo-isomerization to quadricyclane (Q) in it has been achieved. The product maintains the positional and orientational order of the reactant with respect to the polymeric crystallographic axes (see Figure). This system could be suitable for making molecular-sized units in optical data storage systems.