Binding site-driven sensing properties of a quinazoline derivative with metal cations

A compound, 6-furyl-5,6-dihydrobenzoimidazo[1,2-c]quinazoline (L) was synthesized and characterized. L showed weak fluorescence emission at 416 nm in CH3OH when excited by 383 nm. Upon addition of Al3+, Cr3+ or Fe3+ ions, enhanced fluorescence emission and spectral shift (55 nm) could be observed. Job's plot, fluorescence titration, H-1 NMR and ESI-MS data for binding of L with Al3+, Cr3+ and Fe3+ ions showed 1 : 1 metal to L complexation with the transformation of the quinazoline compound (L) to the Schiff base ligand [2-(1H-benzoimidazol-2-yl)-phenyl]-furan-2-ylmethyleneamine (L-1). Cr3+ can be differentiated from Al3+ and Fe3+ by time-dependent fluorescence spectra, while Al3+ can be distinguished from Fe3+ by the emission at 430 nm when excited by 300 nm in the aqueous medium CH3OH-H2O (1/9, v/v). The detection limits were on the order of 10(-6) M for Al3+, Cr3+ and Fe3+ ions. L is insensitive to Cd(II) ions. The crystal structures of Cd(II) complexes, [CdL2(OAc)(2)] (1) and [CdL2Cl2] (2) indicate the binding site of L with Cd(II) is one imidazole nitrogen atom. UV-vis spectra and fluorescence spectra of L, 1 and 2 in CH3OH showed no significant difference. Also H-1 NMR signals of 1 were almost the same as those of L. These observations indicated that the coordination of L with Cd(II) has little effect on the spectroscopic properties of L. The response mechanism of L to Al3+, Cr3+ and Fe3+ ions was discussed.