Metal induced enhancement of fluorescence and modulation of two-photon absorption cross-section with a donor-acceptor-acceptor-donor receptor

A metal ion sensing fluorophore L that exhibits a large two-photon absorption cross-section has been synthesized in good yields. The influences of different metal ion inputs, on the one- and two-photon spectroscopic properties of L, have been investigated. The ligand itself does not show any fluorescence although in presence of a metal ion like Zn(II), Cd(II), Mg(II) or Ca(II), a similar to 25 time enhancement of fluorescence is observed. The ligand with symmetrical donor-acceptor-acceptor-donor characteristics exhibits a large two-photon absorption cross-section measured by femtosecond open-aperture Z-scan technique at 880 nm. However, presence of any of the above metal ions lowers its two-photon absorption cross-section (delta) to different extents at 880 nm. Theoretical calculation carried out in DFT formalism on the ligand and its Zn(II) complex corroborate experimental results. (C) 2007 Elsevier B.V. All rights reserved.