A ligand of Formula (A):






or a carboxylate salt thereof; wherein Y1, Y2 and Y3 each independently represents —COOH or a picolinate of Formula (i):








wherein each R1 independently represents a chromophore group; L1, L2 and L3 each independently represents a single bond or a linker; and X1, X2 and X3 each independently represents a hydrogen atom, a coupling function or a bio-vectorizing group. Also, a process for manufacturing the ligand and to a process for manufacturing a chelate by complexation by the ligand of a rare-earth cation, preferably a lanthanide cation. Further, a use of the ligand and/or the chelate in biological imaging and/or photoluminescence imaging.