Novel fluorogenic and chromogenic three-dimensional ionophores are provided which selectively bond ions such as potassium, sodium, and lithium, even in neutral aqueous or alcohol media. The novel ionophores comprse an "ion-recognizing system" fused to a "signal-moiety" through one or more heteroatoms having a non-bonded electron pair. The signal-moieties are selected from the group consisting of fused ring heterocyclics, fused aromatics, and substituted aromatics having at least one nitro or azo moiety. The ion-recognizing system is a three-dimensional cryptand. The ionophores are ideal for the selective and direct termination of ions in biological or environmental samples and the like.