Two molecular probes for the detection of nucleotides are presented. The positively charged [Tb-DOTAm-Phen]3+ responds only to purine nucleotides and selectively detects GTP and ATP over GDP/GMP and ADP/AMP, respectively. The neutral Eu-DOTA-Phen complex, on the other hand, is selective for purines over pyrimidines but does not distinguish between tri-, di- and monophosphate nucleotides. Both probes possess long luminescence lifetimes that readily enable time-gated experiments and complete removal of any autofluorescence background. The decrease of the Stern–Volmer constants with temperature is indicative of a static mechanism of quenching in agreement with the formation of a stacked phenanthridine–purine complex. The selectivity of the probes for purines over pyrimidines is due to a higher binding affinity and quenching ability of the more extended purines for the phenanthridine chromophore. The selectivity of the positively charged terbium complex for the tri- over the di- and mono-phosphate nucleotides is due to weak electrostatic interactions with the negatively charged phosphates of ATP and GTP, as evidenced by the lack of any selectivity for ATP/ADP/AMP or GTP/GDP/GMP by the neutral europium complex. Both the selective terbium complex and its non-responsive europium analog can be used concomitantly in the same solution as neither probe affects the response of the other. Simultaneous use of the two chemosensors enables more accurate ratiometric detection of ATP to ADP or GTP to GDP conversion and continuous monitoring of kinase reactions.