The present invention relates to substituted-diazenylanilines of the formula I and their nucleotide conjugates, complexes, salts which may be used potentially as fluorescent quenchers in chemical and biological sciences such as cell imaging applications, diagnostics, fluorescent and non-fluorescent tags, pharmaceuticals and other useful applications, and a process of preparing said new compounds. More particularly, the present invention relates to 2,2'-((4-((2,5-disubstituted-4-((4-nitrophenyl)diazenyl)phenyl)diazenyl)-2/3-substituted-phenyl)azanediyl)dialkanol, processes for preparing said compounds and their use as fluorescent quenchers in cell imaging applications, diagnostics, fluorescent and non-fluorescent tags, pharmaceuticals and other useful applications.