Probing metal cations with two new Schiff base bischromophoric pyrene based chemosensors: Synthesis, photophysics and interactions patterns

Abstract Two new pyrene chemosensors (bipyrenyl ligands L 1 and L 2 ) have been synthesized, fully characterized and their sensing ability towards metal cations (Cu 2+ , Ag + , Pb 2+ , Zn 2+ , Cd 2+ and Hg 2+ ) has been investigated by absorption and fluorescence (steady-state and time-resolved) techniques in solution. The absorption spectra of the two free ligands displays a single band (attributed to the monomer absorption) whereas the emission spectra show two bands, which were attributed to the emission of the monomer and dimer. For L 1 , time-resolved fluorescence measurements indicate the presence of a single component that becomes double exponential when the metal ion (in the investigated case, Pb 2+ ) is added. From both steady-state and time-resolved data it is concluded that this dimer likely involves the interaction of two pyrene units, but the absence of a rising component in the fluorescence decays discards the possibility of the presence of a dynamic excimer. Upon addition of a metal ion, this band changes in shape mirroring the fact that a new complex, involving the metal ion and the ligand, is formed. From the overall spectroscopic and photophysical data rationalized by Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) it was concluded that both L 1 and L 2 ligands are able to discriminate Ag + and Pb 2+ from all the other metal ions, with L 2 displaying a higher sensing ability (as seen from HCA/PCA analysis) towards Pb 2+ . This global approach, joining spectral and photophysical data with multivariate analysis, has shown to constitute a powerful tool for revealing important patterns in this type of system.