Addition of 1,3-propane diamine to 2,6-diformyl-4-tert-butyl phenol in ethanol produces a site-selective imination product N,N′-propylenebis(3-formyl-5-tert-butylsalicylaldimine), an acyclic side-off compartmental ligand (H₂L). In the presence of zinc nitrate the ligand goes on hydrolysis in 50 : 50 water–acetonitrile medium and forms a partially hydrolyzed ligand (H₂L′) which slowly metallates to generate a macrocyclic dinuclear zinc(II) complex (1), as characterized by single crystal X-ray analyses. The formation of H₂L′ is believed to occur through the cleavage of an imine bond of the acyclic compartmental ligand (H₂L) in the presence of zinc nitrate which acts as a Lewis acid. The formation of H₂L′ has been monitored by means of ¹H NMR and further confirmed by HRMS spectroscopic studies. The interactions of H₂L with nickel(II) and copper(II) nitrate produce dinuclear complexes 2 and 3 (reported in Inorg. Chem. Commun. 2012, 15, 266–268) respectively, which are formed with unchanged ligand. Various spectroscopic techniques have been used to further characterize the complexes. H₂L hardly exhibits yellowish green fluorescence emission at 523 nm when excited at 437 nm in 1 : 1 water–acetonitrile. Upon addition of Zn²⁺, a new fluorescence emission band at 481 nm appears, the intensity of which slowly enhances. Thus, the ligand H₂L is a ratiometric fluorescence chemodosimeter for the selective detection of Zn²⁺ ions. On addition of Ca^II, Mg^II, Na^I and K^I in the same concentrations as that of Zn²⁺, the emission band at 523 nm is slightly enhanced, whereas the addition of paramagnetic metal cations like Cu^II, Fe^II, Ni^II, Co^II, and Mn^II resulted in quenching of fluorescence. The quenching effect is also observed in the presence of Cd^II, a d¹⁰ metal cation exhibiting similar coordination properties to Zn^II. The Zn^II ion selectivity has also been studied in the presence of other biologically relevant metal ions in 50 : 50 water–acetonitrile.