The present invention provides di-substituted acetalanthraquinone-based compounds of the Formulae (l)-(IV) that are useful for cellular staining and for light-based detection of biological material, e.g. fluorescence-based detection of biological material. These compounds may be used in hydrolysed or non-hydrolysed form. Also provided is a fluorescent complex that comprises a nucleic acid and an acetalanthraquinone-based compound of the invention; and a method of staining a biological sample comprising cells or other biological material containing nucleic acid, which method comprises contacting the biological sample with an acetalanthraquinone-based compound of the invention. In the Formulae (l)-(IV), A and B are each independently of formula —RaCH2CH(ORb)2; or one of A and B is of formula —RaCH2CH(ORb)2 and the other one is of formula: —NRb2.