Photopolymer comprising a new class of photo initator

A photopolymer comprising a photopolymerizable component and a photo initiator system, wherein the photo initiator system comprises a compound according to formula (I)

• in which
• R1 to R6 are independently of each other hydrogen, halogen, alkyl, cyano, carboxyl, alkanoyl, aroyl, alkoxy, aryl, alkoxycarbonyl, aminocarbonyl, which can be further substituted mono- or dialkylamino;
• A is together with X1 and X2 and the atoms connecting them independently of each other a five- or six-membered aromatic or quasiaromatic or partially hydrogenated heterocyclic ring which may each contain 1 to 4 heteroatoms and/or be benzo- or naphtho-fused and/or be substituted by nonionic moieties, in which case the chain attaches to the ring in position 2 or 4 relative to X1,
• X1 is nitrogen, or
• X1—R7 is O or S;
• X2 is O, S, N—R10, C(R11)2 or CR12R13;
• R7 and R10 are independently of each other alkyl, alkenyl, cycloalkyl or aralkyl;
• R11 is hydrogen or alkyl,
• R12 and R13 are independently of each other C1- to C4-alkyl, C3- to C6-alkenyl, C4- to C7-cycloalkyl or C7- to C10-aralkyl or conjointly form a CH2—CH2—CH2—CH2— or CH2—CH2—CH2—CH2—CH2— bridge,
• Q is a monovalent anion;
• R8 and R9 are independently of each other substituents with a Hammett substituent constant σm>0.3
• and B is a connecting group containing 1 or 2 carbon atoms.