A New Benzoxazole-Based Fluorescent Macrocyclic Chemosensor for Optical Detection of Zn2+ and Cd2+

Background: Benzoxazole-containing ligands find many applications both in medicinal chemistry, catalysis and fluorescence chemosensing. Benzoxazole-containing macrocycles could be therefore a good strategy to achieve stable and selective fluorescent complexes with suitable metal ions. In this work, the synthesis, binding, and photochemical properties of a new fluorescent ligand (L) are reported. L is a cyclophane macrocycle containing the 1,3-bis(benzo[d]oxazol-2-yl)phenyl (BBzB) fluorophore and an aliphatic tetra-amine chain to form the macrocyclic skeleton. Methods: Spectrophotometric and spectrofluorimetric measurements, 1H NMR analysis, and DFT calculations were performed. Results: L behaves as a PET-mediated chemosensor, being emissive at 390 nm at acidic pH and non-emissive at basic pH. The chemosensor is able to detect Zn2+ and Cd2+ in an aqueous medium (acetonitrile–water, 4:1 v/v) at neutral pH through a CHEF effect upon metal ion coordination. Paramagnetic metal ions (Cu2+) and heavy atoms (Pb2+, Hg2+) resulted in a quenching of fluorescence or very low emission. Conclusions: The new cyclophane macrocycle L was revealed to be a selective PET-regulated chemosensor for Zn2+ and Cd2+ in an aqueous medium, being able to bind up to two and one metal cations, respectively. The molecule showed a shifted emission towards the visible region compared to similar systems, suggesting a co-planar conformation of the aromatic fragment upon metal coordination. All these data are supported by both experimental measurements and theoretical calculations.

The synthesis and metal binding chemistry of carbahemiporphyrazines with an electron withdrawing substituent

Benziphthalocyanine (bzpc) and dicarbahemiporphyrazine (dchp) are phthalocyanine analogs where one and two of the isoindoline units have been replaced with benzene rings. In this report, we present dchp and bzpc analogs 1 and 2 where CF3 groups have been placed on the 5-position of the benzene rings. Compounds 1 and 2 have identical structural features as their unmodified parent macrocycles, but some differences are observed in their metal adducts. Complex 1Ag shows few differences with the analogous dchp complex, but compounds 1Cu and 2Co exhibit reductions in M – C bond lengths arising from the electron withdrawing nature of the CF3 unit.