This cationic photoinitiator is particularly recommended for use at doses less than 1%, combined with a photosensitiser, e.g. of isopropyl thioxanthone type, for the formulation of inks, pigmented coatings or varnishes applied in thicknesses of greater than 10 microns. It can also be used for the formulation of photopolymers intended for use in applications such as electronics (photoresists, etc.) the graphic arts (printing plates, etc.) composite materials, fibre optics coatings, etc.