Abstract
A terbium complex Tb(PMIP)~3~(PhCN), namely tris(1‐phenyl‐3‐methyl‐4‐isobutyl‐5‐pyrazolone)‐terbium‐(pyrazino[2,3‐f][1,10]phenanthroline‐2,3‐dicarbonitrile), was synthesized as a reagent for anions. Compared with Tb(PMIP)~3~(H~2~O)~2~, the fluorescent quantum yield of Tb(PMIP)~3~(PhCN) was reduced because the triplet energy level of PhCN (20920 cm^–1^)is a little higher than that of ^5^D~4~ of Tb^3+^ (20400 cm^–1^) and lower than that of PMIP (23000 cm^–1^). This resulted in a back‐energy transfer from Tb^3+^ to PhCN. Interestingly, the photoluminescent properties of Tb(PMIP)~3~(PhCN) drastically depend on the nature of the anions added into the solution. When apropos equivalents of fluoride (or acetate) anions were added into the CH~3~CN solution of Tb(PMIP)~3~(PhCN), the replacement of PhCN with fluoride (or acetate) anions took place and the above back‐energy transfer was prohibited, which resulted in a fluorescence enhancement of the terbium complex. After excessive equivalents of fluoride (or acetate) anions were added, the replacement of PMIP with fluoride (or acetate) anions prohibited the ligand PMIP sensitized energy transfer of the terbium complex, resulting in the fluorescence quenching of the system. However, in the aqueous solution, the terbium complex shows a remarkable selectivity of fluoride anions over the other anions. As a reagent, its sensitivity is about 10^–8^ mol·L^–1^ for the fluoride anions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)