Seven difunctional acridinediones DAD were prepared and investigated for their abilities to initiate a ring-opening cationic photopolymerization in combination with an iodonium salt (and optionally N-vinylcarbazole) upon UV/visible light (Xe-Hg lamp; >330 nm) or visible light (halogen lamp) exposure. The structural effects in the DADs and the role of the radical cation are outlined. The cationic and radical photopolymerization of an epoxide/acrylate blend in a one-step hybrid cure leads to the formation of an interpenetrated polymer network. The photochemical mechanisms are studied by fluorescence, steady state photolysis, cyclic voltammetry, electron spin resonance spin trapping, and laser flash photolysis techniques. (C) 2013 Elsevier Ltd. All rights reserved.