Abstract: Disclosed is a method for the photoinitiated transformation of a transformable reactive substrate. The method includes an initial step in which a protected ketone photoinitiator species which is present in the substrate is deprotected to form the corresponding ketone photoinitiator species for use in a subsequent photoinitiated reaction in the method. The ketone group of the photoinitiator is protected by an unsubstituted 1, 3 dioxolane group. Also disclosed are a composition which may be used in the method, the use of the protected ketone photoinitiator in a photoinitiated reaction, as well as the protected ketone photoinitiators themselves.