5-amino-1,10-phenanthroline:: A prototype of tautomeric heterocyclic aromatic chelating fluorophore as ratiometric fluorescent sensor for ZnII

5-amino-1, 10-phenanthroline (5-AP), as a tautomeric heterocyclic aromatic chelating fluorophore (THACF), can sense Zn2+ selectively by shifting emission from 495 to 564 nm upon Zn2+ addition in ethanol. The ratiometric fluorescent sensing behavior has been correlated to the tautomerization of 5-AP affected by solvents and metal chelation. The strategy using THACF as ratiometric fluorescent sensor for Zn2+ not only simplifies the synthetic procedure but also gives a promising alternative for Zn2+ ratiometric fluorescent sensor design.