There is provided a compound of formula (I), wherein R<1>, R<2>, R<3>, R<4>, R<5>, R<6>, R<7>, R<8>, R<9>, X, Y<1>, Y<2>, Y<3>, Z, M, A-B and C-D have meanings given in the description, which are useful in the treatment of medical conditions for which a photodynamic compound is indicated. Compositions, apparatus and methods of treatment of a medical condition for which a photodynamic compound is indicated are also disclosed.