Anthraquinone based near IR emitting compounds and uses thereof

A method of staining a biological sample containing nucleic acid, comprising:

• a) contacting the biological sample with a compound having the structure:
• wherein R2, R3, and R4 are independently OH or NHR9,
• wherein R9 is H or (CH2)nCOR5 and
• R1 is —(CH2)nCOR5,
• wherein R5 is NH(CH2)mNR7R8 or NH(CH2)mN+R7R8R10,
• wherein R7, R8 and R10 are independently H or C1-10 alkyl, m is 2 to 10, and n is 1 to 5 to form a mixture;
• b) incubating the mixture for a sufficient amount of time for the compound to associate with nucleic acid in the sample to form an incubated sample;
• c) exciting the incubated sample by illumination with light of an appropriate wavelength to generate a detectable optical response;
• and
• d) detecting the optical response of the compound.