Abstract: The present invention relates to novel, halogenated psoralen compounds that are useful for inactivating vital contaminants in blood-derived products, particularly blood-derived products that contain platelets or red blood cells. The psoralen compounds of the present invention have the following formula: The side chain S which is a attached to the carbon at position 8 of the psoralen moiety contains a quartemary ammonium group which comprises a central nitrogen atom, a linking group L, and an aromatic ring structure. The linking group L joins the central nitrogen atom of the quartenary ammonium group to the psoralen moiety. The linking group L comprises a carbon chain having 2 to 12 carbon atoms and an oxygen atom which links the carbon chain to the psoralen moiety. The psoralen compounds of the present invention also comprise one or more halogens attached to the psoralen moiety. Preferably the halogens are attached to the carbon atom at position 3 or 5 of the psoralen moiety.