Replacement of quinolines with isoquinolines affords target metal ion switching from Zn to Cd in the fluorescent sensor TQLN (N,N,N',N'-tetrakis(2-quinolylmethyl)-2,6-bis(aminomethyl)pyridine).

A quinoline-based heptadentate ligand, N,N,N',N'-tetrakis(2-quinolylmethyl)-2,6-bis(aminomethyl)pyridine (TQLN), exhibits a Zn-specific fluorescence increase at 428 nm, which is assigned to excimer emission (I/I = 38, I/I = 24%, ϕ = 0.069). In contrast, the isoquinoline counterpart 1-isoTQLN exhibits a Cd-specific fluorescence increase at 365 nm attributable to monomer emission (I/I = 83, I/I = 19%, ϕ = 0.