The unprecedented one-dimensional (1-D) coordination polymer of crown fused zinc phthalocyanine (P-CfZnPc) with an octahedral crystal structure and with intermolecular packing that has superior multichannel sensor ability for Be2+ ion recognition was prepared and characterized by single-crystal X–ray diffraction analysis (XRD) and a wide range of spectroscopic and voltammetric methods. An exceptional feature of the crystal structure of P-CfZnPc is that each zinc ion in the phthalocyanine (Pc) polymer is coordinated by the four isoindole nitrogen atoms and an outer oxygen atom of the Pc molecule. This structure is the first example of an octahedral arrangement in a 1-D polymeric chain for zinc phthalocyanines (ZnPcs) and zinc porphyrins (ZnPs) reached without the presence of a coordinating solvent, which was confirmed by XRD analysis. Interestingly, this (1-D) coordination polymer preserves its conformation in THF (tetrahydrofuran) solution, thereby effectively preventing aggregation. This result was confirmed by the particle size of the molecule (125 nm) using dynamic light scattering (DLS) and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectra as well as UV–vis spectroscopy. The sensor has long-term stability (more than 3 months in solution), a very low response time (less than 1 s), and nonaggregating ability, facilitating the accurate determination of ultra-trace amounts of Be2+ (lower than 1 ppb), which is extremely important in terms of human health and environmental protection. The sensor can highly selectively and sensitively bind Be2+ among Li+, Na+, K+, Cs+, Mg2+, Ca2+, Ba2+, Al3+, Co2+, Hg2+, Ni2+, Pb2+, and Zn2+ ions via Be2+-induced J aggregation of Pc molecules. Such a binding leads to not only a significant decrease in Pc absorption (677 nm) as well as the creation of new absorption (720 nm) but also fluorescence emission quenching (690 nm). Furthermore, the sensor displayed highly selective voltammetric recognition for Be2+ following J aggregation/disaggregation in the second reduction process. The binding mechanism of the sensor and Be2+ ion was also explained on the basis of TD-DFT calculations.

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We explored the mechanistic aspects of ion pair formation between electrochemically reduced radicals (Fc-cnq-1a • − /Fc-cnq-1b • −) and dianions (Fc-cnq-1a 2− /Fc-cnq-1b 2−) of ferrocenyl naphthoquinones (Fc-cnq-1a and Fc-cnq-1b) and several metal ions by cyclic voltammetry (CV), square wave voltammetry (SWV) and spectroelectrochemistry, for the first time. The experiments demonstrated that Fc-cnq-1a 2− /Fc-cnq-1b 2− were moderately affected with Na + , K + and Cs + by slightly shifting to the anodic side, but were strongly influenced with Li + ion. Fc-cnq-1a • − /Fc-cnq-1b • − were not affected by alkali metal ions, indicating no ion pair formation between the radicals and these ions. Fc-cnq-1a 2− /Fc-cnq-1b 2− was not evolved in the presence of Be 2+ , Mg 2+ and Ca 2+ , but Fc-cnq-1a • − /Fc-cnq-1b • − appeared with their cathodic waves, and participated with intermediates, [(Fc-cnq-1b) 2 • −-Be 2+ and [(Fc-cnq-1a) • −-Cl]. The most pronounced effect on the ion-pair formation of the Fc-cnq-1a • − /Fc-cnq-1b • − was observed in Be 2+ , indicating that Fc-cnq-1a or Fc-cnq-1b can selectively sense ultra-trace amount of Be 2+ (LOD = 3.6 ppb) among the other metal ions with SWV titration, for the first time, based on the strong ion pair formation reaction between the radicals and Be 2+ .

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