Universite de Haute-Alsace 1 article published in JoVE Chemistry Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization Julien Pinaud1, Emeline Placet1, Patrick Lacroix-Desmazes1, Thi Kim Hoang Trinh2,3, Jean Pierre Malval2,3, Abraham Chemtob2,3, Loïc Pichavant4, Valérie Héroguez4 1ICGM, Université de Montpellier, CNRS, ENSCM, 2Institut de Science des Matériaux de Mulhouse (IS2M UMR 7361 CNRS), Université de Haute-Alsace, 3Université de Strasbourg, 4Laboratoire de Chimie des Polymères Organiques (LCPO UMR 5629 ENSCBP), Université de Bordeaux We describe a protocol to photogenerate N-heterocyclic carbenes (NHCs) by UV irradiation of a 2-isopropylthioxanthone/imidazolium tetraphenylborate salt system. Methods to characterize the photoreleased NHC and elucidate the photochemical mechanism are proposed. The protocols for ring-opening metathesis photopolymerization in solution and miniemulsion illustrate the potential of this 2-component NHC photogenerating system.