Photopolymer formulations for producing holographic media having highly crosslinked matrix polymers

A photopolymer formulation comprising a polyol component, a polyisocyanate component, a writing monomer and a photoinitiator containing a coinitiator and a dye of formula

• F+An−,
• where
• F+ represents a cationic dye selected from the group consisting of acridine, xanthene, thioxanthene, phenazine, phenoxazine, tri(het)arylmethane, diamino(het)arylmethane, triamino(het)arylmethane, monomethinecyanine, dimethinecyanine, trimethinecyanine, hemicyanine, nullmethine, naphtholactam and streptocyanine dyes, and
• An− is sec-C11- to C18-alkanesulphonate, C13- to C25-alkyl sulphate, branched C8- to C25-alkyl sulphate, optionally branched bis-C6- to C25-alkyl sulphosuccinate, sec- or tert-C4- to C25-alkylbenzenesulphonate, sulphonated or sulphated, optionally mono- or polyunsaturated C8- to C25-fatty acid esters of aliphatic C1- to C8-alcohols of glycerol, bis(sulpho-C2- to C6-alkyl) C3- to C12-alkanedicarboxylic esters, or (sulpho-C2- to C6-alkyl) C6- to C18-alkanecarboxylic esters,
• wherein the dye of formula F+An− has a water imbibition of ≦5%, and wherein the anion An− has an AClogP in the range of 1-6.5.