A xanthene compound is used for discriminating living from non-living unicellular and multicellular organisms. The xanthene compound is represented by the following formula (I)whereineach X is, independently from each other, one of H, F, Cl, Br, I, CN；Z is one of O, Si, Ge or Sn；R1 is hydrogen, -(C=O)-R4 or -CH2-O-(C=O)-R4, wherein R4 is substituted or unsubstituted alkyl having 1 to 18 carbon atoms, substituted or unsubstituted alkenyl having 2 to 18 carbon atoms, or substituted or unsubstituted aralkyl having at least 7 carbon atoms, or wherein R1 is a residue derived from an amino acid, peptide, nucleotide or oligonucleotide, monosaccaride or polysaccharide；A is -NH2, -OR1 or -NR5(C=O)-R4 wherein R4 independently has the meaning as defined above and R5 is H, substituted or unsubstituted alkyl having 1 to 18 carbon atoms, substituted or unsubstituted alkenyl having 2 to 18 carbon atoms, or substituted or unsubstituted aralkyl having at least 7 carbon atoms；R2 and R3 are, independently from each other, H or -(C=O)-NR6R7, wherein at least one of R2 and R3 is not H, and wherein R6 and R7 are selected from H, substituted or unsubstituted alkyl having 1 to 18 carbon atoms, substituted or unsubstituted alkenyl having 2 to 18 carbon atoms, or substituted or unsubstituted aralkyl having at least 7 carbon atoms.
