Abstract
DB‐cyclen [1,7‐bis(phenylmethyl)‐1,4,7,10‐tetraazacyclododecane] was investigated in 50 % CH3OH/H2O (v/v) as a fluorescent sensor for heavy metal ions, and as the CdII complex as a sensor for anions. The PbII complex showed a unique strong emission at 447 nm, possibly a charge‐transfer band involving the 6p←6s2 transition of PbII and the benzyl fluorophore. ZnII uniquely produced a significant emission at 353 nm, suggested to be due to an aggregation induced (AIE) mechanism, possibly involving exciplex formation. The free DB‐cyclen ligand produces a fluorescence band at 354 nm above pH ca. 9, accompanied by the slow formation of an aggregate in suspension as indicated by the presence of light scattering peaks in the absorbance spectra, an AIE effect, due to formation of an intermolecular exciplex in the solid state. The role of M···C π contacts in quenching fluorescence in DB‐cyclen complexes or in AIE effects was investigated in the structures of [Pb(DB‐cyclen)(ClO4)2] (1), [Cu(DB‐cyclen)(ClO4)2] (2), [Ag(DB‐cyclen)(ClO4)] (3), and [Cd(DB‐cyclen)(ClO4)(H2O)]ClO4 (4). In 1 there is an intermolecular π contact between the PbII and a benzyl group from an adjacent complex individual, which is also the case in 3, where very short η2 intermolecular Ag···C π contacts are found. A strong band at 336 nm is shown in the CdII DB‐cyclen complex on titration with Cl– only: Br–, I–, S2O32–, and SCN– produced no AIE/exciplex band in the CdII DB‐cyclen complex: the exciplex forming species may be a Cl– bridged dimer [Cd(DB‐cyclen)Cl]22+.
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