Fluoroionophores that are functionalised with reactive groups and correspond to the formula I—R1—F—R2—G, wherein I is a monovalen residue of an ionophore, wherein F is a divalent residue of a fluorophore, wherein G is a functional group and R1 and R2 are each independently of the other a direct bond or a bridging group. The fluoroionophores may be covalently bound to carrier materials and are used as active components in polymer membranes of optical sensors for the detection of ions. The sensors are distinguished by a long usable life and a high degree of sensitivity.