A new phosphorescent iridium(III) complex [Ir(Bpq)2(bpy)](+)PF6(-) based on cyclometalated ligands (Bpq) containing a dimesitylboryl group was synthesized and characterized by photophysical and electrochemical studies. The excited-state properties of Bpq and [Ir(Bpq)2(bpy)](+)PF6(-) were investigated using molecular orbital calculations. Importantly, both Bpq and [Ir(Bpq)2(bpy)](+)PF6(-) could be used as highly selective chemosensors for a fluoride anion (F(-)) detected by the naked eye, owing to the interaction of the dimesitylboryl group (BMes2) with F(-). For the Bpq ligand, a red shift of the emission spectrum was observed upon the addition of F(-), which could be attributed to an excited-state switch from a pi-pi* transition to a charge-transfer transition upon complexation with F(-). The addition of F(-) to a solution of [Ir(Bpq)2(bpy)](+)PF6(-) induced a change in the solution color from yellow to orange-red and phosphorescent quenching, indicating that [Ir(Bpq)2(bpy)](+)PF6(-) could act as an excellent ON-OFF-type phosphorescent chemosensor for F(-).