Novel assays for ligands and receptors employing novel compounds that are conjugates of squarates dyes and members of a specific binding pair (sbp) are disclosed. The sbp members are selected from the group consisting of ligand and its complementary receptor. The sbp member is covalently or non-covalently bound to the squarate dye, which usually has an absorption maximum greater than 600 nanometers. The novel conjugates are employed in assays for determining the presence or amount of an sbp member analyte in a sample suspected of containing such analyte. Kits comprising such novel conjugates are also disclosed.