Photophysical and density functional studies on a nitrobenzoxadiazole-based system, 4-(2-diphenylphosphinoethylamino)-7-nitro-2,1,3-benzoxadiazole (1), have been carried out in acetonitrile medium to determine the nature of interaction between 1 and different biologically and environmentally relevant metal ions. Quantum mechanical calculations have been carried out to find out the molecular origin of fluorophore-metal interactions. Higher fluorescence enhancement values of the system in presence of Fe(III) and Cr(III) has been attributed to the stabilization interactions between the P-atom of the receptor with M(III) as well as the pi-overlapping of the aromatic rings (through the formation of eta(6) complexes). (C) 2012 Elsevier B.V. All rights reserved.