A quinoline-based hexadentate ligand, (S,S)-N,N,N',N'-tetrakis(6-methoxy-2-quinolylmethyl)-1,2-diphenylethylenediamine ((S,S)-6-MeOTQPh(2)EN), exhibits fluorescence enhancement at 498 nm upon addition of 1 equiv of Zn2+ (I-zn/I-0 = 12, phi(zn) = 0.047) in aqueous DMF solution (DMF/H2O = 2:1). Addition of 1 equiv of Cd2+ affords a much smaller fluorescence increase at the same wavelength (I-cd/I-0 = 2.5, I-cd/I-zn = 21%). The trivalent metal ions such as AI(3+), Cr3+, and Fe3+ also exhibit fluorescence enhancement at 395 nm (I-AI/I-0( )= 22, I-Cr/I-0 = 6 and IFe3+/I-0 = 13). In contrast, meso-6-MeOTQPh(2)EN exhibits a Cd2+-selective fluorescence increase at 405 nm in the presence of 1 equiv of metal ion (I-cd /I-0 = 11. 5 phi(cd) = 0.022), while Zn2+ induces a smaller fluorescent response under the same experimental conditions (I-zn /I-0 = 3.3, I-zn/I-cd = 29%). In this case, the fluorescence intensities of meso-6-MeOTQPh(2)EN in the presence of a large amount of Zn2+ and Cd-2+ become similar. This diastereomer-dependent, fluorescent metal ion specificity is derived the Zn2+-specific intramolecular excimer formation in (S,S)-6-MeOTQPh(2)EN-Zn2+ complex and higher binding affinity of meso-6-MeOTQPh(2)EN with Cd2+ in comparison to Zn2+. The more conformationally restricted diastereomeric pair, namely, cis- and trans-TQDACHs (cisand trans-N,N,N',N'-tetrakis(2-quinolylmethyl)-1,2-diaminocyclohexanes), both exhibit Zn2+-specific fluorescence enhancement because of the high metal binding affinity and intramolecular excimer forming property derived from the rigid DACH backbone.