Tryptophan moiety based tetranuclear Ni(II) complex: synthesis, crystal structure and fluorescence sensing

Tryptophan moiety based Schiff base [H2L = N-(2-(hydroxy)-3-ethoxybenzylidene)tryptophan] was used to synthesize a tetra nuclear Ni(II) complex, namely [Ni4(L)4(dmf)(H2O)3].4(dmf).4(H2O) [dmf = dimethylformamide], which has been characterized by X-ray single crystal diffraction, electronic spectra and IR spectral techniques. The luminescent properties of the complex, examined in various organic solvents, highlighted that the metal complex displays a selective response toward nitroaromatic compounds, especially towards picric acid (PA), for which a LOD value of 3.93x10-7 M was calculated. The fluorescence sensing mechanism was investigated by fluorescence lifetime measurement and DFT calculations. The results showed that selective fluorescence sensing may be due to a combined effect of energy and electron transfer as well as electrostatic interaction.