The present invention discloses the compounds of general Formula-A [C20H20CuN4O(R)2 wherein, R= NO3 or Cl] and its method of preparation. The compound of  general Formula-A is used for selective detection of homocysteine in aqueous medium at physiological pH (7-7.5) even in the presence of other competing species such  as alanine, methionine, threonine, proline, leucine, isoleucine, lysine, phenylalanine, hydroxyproline, asparagine, arginine, serine, valine, cysteine, glutathione  (reduced), glycine, histidine, and glutamine. The compounds of general Formula-A exhibit high selectivity towards homocysteine without any interference from other  challenging biomolecules. Using the compounds of general Formula-A, specific detection of homocysteine under UV light in aqueous solution is also possible by the  naked eyes.