Among those are anthraquinone-2-sulfonic acid (AQ-2-SO3 H), 2,6- or 1,5-disulfonic acid (AQ-2,6-diSO3 H; AQ-1,5-diSO3 H) and their derivatives and other members of the anthraquinone group substituted by electron-withdrawing moieties such as chlorine atoms, and also benzoquinone and benzanthrone.6,7