Reducing the Hydrogen Atom Abstraction Efficiencies of Benzophenone-Based Photosensitive Alkoxyamines

Abstract : The work reported herein details the synthesis, as well as the photophysical and photochemical investigation, of novel benzophenone-based photosensitive alkoxyamines for potential application in nitroxide-mediated photopolymerization. As benzophenone has found widespread application in photosensitive alkoxyamines, serving as an intramolecular photosensitizer, the deleterious effects of competitive excited state hydrogen atom abstraction processes are examined. In order to reduce the efficiency of excited state hydrogen atom abstraction processes, electron donating methoxy and pyrrolidine substituents were incorporated para to benzophenone's carbonyl moiety to modulate the excited state character of the substituted benzophenone motifs. Whilst the incorporation of electron donating substituents reduced the efficiency of excited state hydrogen atom abstraction processes, this did not translate into increased photo-dissociation efficiencies. Greater photo-dissocia tion efficiencies were obtained for benzophenone-based alkoxyamines lacking the electron donating functionalities. The excited state character of the benzophenone moiety is therefore a key parameter governing both the hydrogen atom abstraction and photo-dissociation efficiencies of benzophenone-based photosensitive alkoxyamines.