Design and synthesis of novel fluorescence sensing perylene diimides based on photoinduced electron transfer

Two novel tetraester- and PAMAM-branched perylene diimides were synthesized and configured as ``fluorophore-spacer-receptor{''} systems based on photoinduced electron transfer. Due to their long alkylester and alkylamine terminal groups the examined compounds were well soluble in organic solvents. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (1:1, v/v) solution. The ability of the synthesized perylene diimides to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Zn(2+), Co(2+), Cu(2+), Fe(3+), Pb(2+), He(2+), Ag(+) and Ni(2+)) and protons. The dyes under study displayed ``off-on{''} switching in its fluorescence as a function of pH, which is attributed to disallowing photoinduced electron transfer from the receptor moiety to the fluorophore. PAMAM-branched dye displayed a good pH sensor activity (FE = 6.4), however the pH sensing ability of tetraester was substantially higher (FE = 184). In the presence of Cu(2+) and Pb(2+) ions tetraester quenched its fluorescence intensity (FQ = 22 and 12 respectively), while PAMAM-branched dye enhanced its fluorescence intensity with pronounced selectivity to Cu(2+) and Fe(3+) (FE = 3.2 and 4.9, respectively). The results obtained indicate the potential of the novel compounds as fluorescent detectors for metal ions with pronounced selectivity towards Cu(2+), Pb(2+) and Fe(3+) ions and highly efficient ``off-on{''} pH switches, especially a tetraester-branched perylene diimide. (C) 2011 Elsevier Ltd. All rights reserved.