rogen atoms is excluded, the case wherein R7 and A1 are methoxy groups or A2 and R6 are methoxy groups is excluded, when n is 1; at least R1, R2, R4 and R9 are groups other than hydrogen atom, or at least R3, R5, R8 and R10 are groups other than hydrogen atom, the case wherein R3 and R10 or R4 and R9 are an aryl group which may optionally be substituted is excluded; and when n is 2, the formula (I