A tetra-(bipyridylphenyl)porphyrin for luminescence sensing of divalent metal ions

The fluorescence quenching of a tetra-(bipyridylphenyl)porphyrin (la) by va rious metal ions in DMSO solutions is discussed. In all cases quenching res ults via formation of a ground state complex between a bipyridyl moiety of the porphyrin and the metal ion. For Zn(II) tetra(bipyridylphenyl)porphyrin (Ib) luminescence quenching is only observed with Co(II), NL(II) and Cu(II ). In all three detectable quenching is observed at sub-part per million co ncentrations. For luminescent species having multiple, independent, metal i on binding sites (like Ib), detailed examination of the luminescence quench ing clearly shows that association equilibria for binding metal ions at at least two of the available sites must be taken into account. The quenching of Ib with Cu(II) was examined in detail and the rate constant for quenchin g was determined using picosecond time resolved absorption spectrophotometr y. The mechanism of the quenching process is discussed in each case. Metal ion selectivity is obtained for this system as a result of both thermodynam ic and kinetic Limitations to quenching the luminescence of 1b. (C) 1999 El sevier Science S.A. All rights reserved.