The coordination chemistry of three new quinoline pendant arm derivatives of [9]aneN(3) (L-1, L-2) and [9]aneN(2)S (L-3) toward Cu-II, Zn-II, Cd-II, Hg-II, and Pb-II has been investigated both in solution and in the solid state. The protonation constants for L-1-L-3 and stability constants with the aforementioned metal ions have been determined potentiometrically in 0.10 M NMe4Cl MeCN/H2O (1:1 v/v) Solution at 298.1 +/- 0.1 K; the measured values show that Cu-II has the highest affinity for all three ligands, followed by Zn-II, Hg-II, Pb-II, and Cd-II. For each metal ion considered, 1:1 complexes with L-1-L-3 have also been isolated in the solid state and [Cu(L-1)](BF4)(2) (1), [Zn(L-1)](BF4)(2) (2), [Cd(L-1)](ClO4)(2) (3), [Hg(L-1)](NO3)(2) (4), [Pb(L-1)](ClO4)(2)center dot MeCN (5), [Zn2Cl2(L-2)(2)](BF4)(2)center dot 1/2MeNO(2)center dot H2O (6), [Cu(L-3)](ClO4)(2) (7), [Zn(L-3) (NO3)]NO3 (8), [Cd(L-3)(NO3)(0.82)Cl-0.18]NO3 (9), and [Hg(L-3)](ClO4)(2)center dot MeCN (10) have also been characterized by X-ray crystallography. The optical response of L-1-L-3 to the presence of the above-mentioned metal ions has been investigated in MeCN/H2O (1:1 v/v) and H2O solutions. All three ligands show a stronger "OFF-ON" CHEF (chelation enhancement of fluorescence) effect in the Zn-II complexes than in the Cd-II complexes in both media. The results have been examined by considering the ratio I-rel(Zn-II)/I-rel(Cd-II), within the emerging idea that the relative strength of the CHEF effect for the small Zn-II ion as compared to larger Cd-II ion might be determined by steric crowding in the corresponding complexes with quinoline-based fluorescent chemosensors.