The　solid　state　[2　+　2]　photocycloaddition　of　N,N＇-diacyl-1,4-dihydropyrazines　has　been　investigated　using　thiourea　as　a　template　to　preorient　the　reactants　in　the　crystalline　state　in　a　manner　that　is　beneficial　for　the　[2　+　2]　photocycloaddition.　The　structures　of　the　photoadducts,　syn-dimers　and　cage-dimers,　were　determined　using　NMR　and　single-crystal　X-ray　diffraction.　According　to　the　topochemical　principles　used　to　assess　the　feasibility　of　solid　state　photochemical　[2　+　2]　cycloaddition,　topological　analysis　of　cocrystals　consisting　of　the　N,N＇-diacyl-1,4-dihydropyrazines　and　thiourea,　as　well　as　the　syn-dimers,　was　performed　to　investigate　the　influence　of　packing　modes　and　non-covalent　interactions　on　their　solid　state　photo-reactivity.　The　results　showed　that　the　solid　state　[2　+　2]　reactivities　of　both　the　N,N＇-diacyl-1,4-dihydropyrazines　assembled　using　thiourea　and　the　syn-dimers　were　controlled　by　the　topochemical　orientation　of　the　potentially　reactive　double　bonds　and　the　H-bonding　interactions　within　the　adjacent　reactive　molecules.