Synthesis, characterization and metal ion-sensing properties of two Schiff base derivatives.

Abstract Two new Schiff base derivatives {2,2′-diphenyl- N , N ′-bis(2-pyridylmethylene)biphenyl-4,4′-diamine} ( 1 ) and {2,2′-diphenyl- N , N ′-bis(salicylidene)biphenyl-4,4′-diamine} ( 2 ) were synthesized and characterized by means of elemental analysis, 1 H NMR, FT-IR, and standard spectroscopy techniques. The molecular structure of 2 has been determined by X-ray single crystal analysis. The analyses of fluorescence properties of the compounds revealed that 1 and 2 are both poorly fluorescent and display sensitive fluorescence responses to a panel of 24 monovalent, divalent, and trivalent metal ions in CH 3 CN–DMSO (9:1, v/v). Results with imine 1 showed that Fe 3+ , Cu 2+ , Zn 2+ , Cd 2+ , Mn 2+ , Zr 4+ , Hg 2+ , Cr 2+ , Pb 2+ , Sn 2+ , Bi 2+ , Al 3+ , Ce 3+ , La 3+ , Sm 3+ , Gd 3+ , Nd 3+ , Eu 3+ and Dy 3+ yields red shifts in emission and increases in intensity. And the greatest spectral changes for imine 2 include enhancements in emission intensity coupled with red shifts (Zr 4+ , Sn 2+ , Al 3+ and Zn 2+ ) and strong quenching (Fe 3+ ). The fluorescence enhancement mechanism of 1 and 2 for metal ions is based on: (i) C N isomerization; (ii) chelation-enhanced fluorescence (CHEF) effect; and (iii) excited-state intra/intermolecular proton transfer (ESPT).