Solvent‐Free Photosynthesis of Cyclobutanes: Photodimerization of Crystalline Olefins

1 Introduction 2 Photodimerization of Cinnamic Acids: Emergence of Topochemical Postulates 3 Photodimerization of Coumarins, Styrylcoumarins and Benzylidenecyclopentanones 4 Reaction Cavity Concept: Role of Empty Space and Immediate Neighbors 5 Fine Tuning of Topochemical Postulates 6 Impact of Excitation on Molecular Geometry and Intermolecular Arrangement 7 Crystal Engineering 8 Does Dimerization Precede Geometric Isomerization? 9 Single Crystal to Single Crystal Photodimerization of Olefins 10 Concluding Remarks 11 Appendix: More Examples of Solid State Photodimerization of Olefins 12 Acknowledgment Keywords: olefin photodimerization and cyclobutanes in crystals; cinnamic acid photodimerization; reaction cavity concept; topochemical postulates; static concept of preorganization; crystal engineering; dimerization preceding geometric isomerization; single crystal to single crystal (SCSC)