a novel compound with anthraquinone structure and having the following foluma : wherein r 1 , r 2 and r 3 each independently is hydrogen , hydroxy , amino or c 1 - 6 alkyl group ; r 4 is hydrogen , c 1 - 18 alkyl carbonyl , c 1 - 6 alkyl group substituted by at least a functional group ; r 5 is hydrogen amino or a group of the following formula wherein r 1 , r 2 , r 3 and r 4 are defined as the above ; and r and r ′ each independently is hydrogen , hydroxyl , amino , c 1 - 6 alkyl group or a group of the following formula wherein r 1 , r 2 , r 3 and r 4 are defined as the above .