Synthesis, characterization, solid state and aqueous solution fluorescence study for lanthanide-crown ether-terpyridine complexes

The complexes [Eu(12-crown-4)(terpy)(H2O)]3Cl, [Eu(15-crown-5)(terpy)]3Cl, [Tb(12-crown-4) (terpy)(H2O)]3Cl, [Tb(15-crown-5)(terpy)]3Cl, [Gd(12-crown-4)(terpy)(H2O)]3Cl and [Gd(15-crown-5)(terpy)]3Cl (terpy 2,2',6',2''-terpyridine) were synthesized and characterized by CHN elemental analysis, infrared spectroscopy and fluorescence spectroscopy. Emission spectra were obtained on both, solid state and aqueous solutions for europium and terbium complexes. The complexes exhibit good emission, even in aqueous solution, enhancing their potential for biological applications. The reduction of emission intensity, from solid state to aqueous solution, is lower for europium complexes, in comparison to terbium complexes. The [Eu(12-crown-4)(terpy)(H2O)] (.) 3Cl complex exhibits an emission lifetime of 0.64ms while [Eu(15-crown-5)(terpy)] (.) 3Cl exhibits a value of 0.38ms. Furthermore, the 15-crown-5 complex emission intensity is about 3.8 times larger than the emission intensity of the 12-crown-4 complex. This ratio (3.8) is the same as observed for the A(RAD) and A(NRAD) for the aqueous solutions: 1225.5/339.5 = 3.6. The aqueous solution quantum yield is higher for [Eu(12-crown-4)(terpy)(H2O)]3Cl in comparison with [Eu(15-crown-5)(terpy)]3Cl, suggesting that 12-crown-4 exhibits a more suitable ratio than 15-crown-5.