Seven fluorine-substituted 1H-pyrrolo [2, 3-b] pyridine derivatives were synthesized based on a lead ligand, 3-[[4-(4-iodophenyl) piperazin-1-yl]-methyl]-1H-pyrrolo [2, 3-b] pyridine (L- 750,667) and evaluated as potential dopamine D4 receptor imaging agents by positron emission tomography (PET). Binding affinities of these ligands for the dopamine D2, D3, and D4 receptor subtypes were measured in vitro. Most ligands showed high and selective ...