the invention relates to a compound having the general formula i ## str1 ## in which one of the groups r 1 , r 2 , r 3 , r 4 , r 5 , r 6 and r 7 represents an ionophoric moiety and the remaining groups each independently are hydrogen , a lipophilic or hydrophilic group or a reactive group for coupling to a polymer or a biomolecule , or r 2 forms an aromatic ring system together with r 3 and r 5 forms an aromatic ring system together with r 6 . the compound of the invention is useful as a luminescence indicator for alkali ions .