Fluorescence Ratiometry of Monomer/Excimer Emissions in a Space-Through PET System

Fluorescence and metal-ion recognition properties of acetylacetone-based ligands

A new acetylacetone-based ligand (Ligand 1) bearing pyrene unit was synthesized and the fluorescence and metal-ion recognition properties were investigated in the presence of a different metal ion in acetonitrile solution. The fluorescence emission of Ligand 1 was strongly quenched by complexation with Cu(2+) while no significant change was observed in the presence of other metal ions. The metal-ion selectivity changed from Cu(2+) to Ni(2+) when glycine moiety (-NH-CH2-CO-) was introduced into Ligand 1 as spacer. This result implies that hydrogen-bonding induced by the glycine moiety affects the binding ability of ligands to metal ions, resulting in change of the metal-ion selectivity.

Ion-Induced FRET On−Off in Fluorescent Calix[4]arene

A novel calix[4]arene bearing one 2,3-naphthocrown-6 and two coumarin amide units at the lower rim in partial-cone conformation was synthesized as a colorimetric and FRET-based fluorometric sensor for F(-) and Cs(+) ions. Intramolecular FRET from the naphthalene emission to the coumarin absorption affords high fluorescence selectivity toward F(-) and Cs(+) ions.

Diastereodifferentiation of Novel Naphthalene Dyads by Fluorescence Quenching and Excimer Formation

Four new bichromophoric naphthalene dyads in form of diastereomeric pairs are synthesized and photophysically characterized. For a closely related group of compounds (NAP-NAP, MNAP-NAP, MNAP-MNAP), systematic variation of the urea linker led to the observation of intramolecular fluorescence quenching for tertiary urea, but not for secondary urea. Chiral information contained in the dyads has an impact on the efficiency of this process. Furthermore, for the case of (R,R)-MNAP-MNAP, excimer formation in the pre-organized dyad was noted, while being absent in the corresponding (R,S) diastereomer. These differences in photophysical behavior are ascribed to the geometry of the linker and to the chiral information contained in the diastereomeric compounds. Other dyads, such as NPX-NPX, included naproxen as the chromophore. For these compounds strong excimer emission is obtained, however, only very small diastereodifferentiation is observed for the two investigated stereoisomers.