A particularly preferred embodiment of the present invention relates to compounds of the formula Z , wherein A is a group of the formula 1_, wherein one of the CH moieties at positions a and b of formula 1_ may be replaced bv a nitroqen atom, or A is a group of the rormula 3_; B is a group of the formula 1_ or 8_; R 1, R2, 3 1 2 3 R , q, Y , Y and Y are as defined for formula I; and n is 1 or 2; w