Unprecented octahedral crystal structure of one dimensional coordination polymer crown fused zinc-phthalocyanine and its trace amount Be2+ detection by double channel sensor

Abstract

Professor Reginald P. Linstead was the first to use the name of phthalocyanine (Pc) in 1933 for defining the organic compound class consisting of metal-free and metallophthalocyanines and their derivatives. The phthalocyanine, which is large enough to accommodate many metal ions, is a symmetrical macrostructure formed by four iminoisoindoline units containing two imino hydrogen atoms and four nitrogen atoms in the pyrrole rings directly take parts into the complex formation. Phthalocyanines are photochemically and photophysically stable macrocycle and enable the phthalocyanine-based molecules are, and long-lived. With its 18π electronic system, this structure has intense absorption and emission in the visible region. These properties can be sensitively changed by adding groups having specific properties and modifying the number of such groups to the peripheral position of phthalocyanine macrocycle or by interfering with the center metal. As macrocyclic polyethers, the crown ethers were for the first time synthesized by Pedersen in 1967. From 1967, Pedersen formed bridges of cyclic ethers ranging from 4 to 20 oxygen atoms with ethylene and propylene. Besides the oxygen hetero-atom derivatives, different heteroatom derivatives such as azacrown ethers and thiacrown ethers have been synthesized and their complexation properties with metal cations have been investigated. Due to the tunable donor atoms of the crown ethers, many different metal cations can be selectively bound and analyzed. In addition to the ability to bind metal cations, crown ethers for use as phase transfer catalysts and chemical sensors make a special compound in many fields. Beryllium is the most toxic metal known to be used in the industry and in many areas like defense, aerospace, automotive, petrochemical, telecommunications and nuclear reactor industry, which is extremely important for not only human health but also environmental protection. Beryllium is an occupational disease factor and Chronic Beryllium Disease (CBD) occurs in workers who are exposed to certain doses of beryllium. Exposed to high doses of beryllium causes acute lymphocytic pneumonia, which is not yet possible to treat in individuals. In the classification of the agents causing cancers by the International Agency for Research on Cancer (IARC), beryllium has been classified in the 2A group (proven to be causally causative of cancers in experimental animals and humans). When compared to beryllium with other toxic metal cations like Cd and Pb, the amount of exposure allowed in work areas is 100 times less. For these reasons, especially in areas where there is heavy industrialization, beryllium is extremely important in terms of human health and determination of trace amount beryllium is a significant necessity. In this context, unprecented octahedral crystal structure of one dimensional coordination polymer crown fused zinc-phthalocyanine P-CfZnPc with intermolecular packing, double channel and ratiometric sensor, was prepared and used to highly selective and sensitive recognition of Be2+ ion in this study. P-CfZnPc which was formed by self-assembled during the reaction was characterized on the basis of single crystal X-ray diffraction analysis and by a wide spectroscopic methods, including MALDI-TOF mass spectra, NMR, Electronic absorption and IR spectroscopy. An interesting feature of the crystal structure of P-CfZnPc is that each zinc ion in the phthalocyanine polymer to be hexa-coordinated by the four isoindole nitrogen atoms and crown oxygen atoms of an outer phthalocyanine ring, causing the structure to possess the first example of octahedral arrangement without solvent for zinc phthalocyanine (ZnPc). Interestingly, this polymeric structure remains its conformation in THF solution thereby effectively preventing aggregation which was confirmed with particle size of molecule (125 nm) using Dynamic Light Scattering (DLS) and MALDI-TOF mass spectra as well as UV-vis spectroscopy. This double channel and ratiometric sensor having long-term stability, P-CfZnPc, was enabled us to accurately determine ultra-trace amount of Be2+, the most toxic metal known to be used in the industry and in many areas, and 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+, Cu2+, Fe2+, and Zn2+ ions via Be2+-induced J-aggregation of phthalocyanine molecules, leading to not only significant decrease of phthalocyanine absorption (677 nm) as well as creating new absorption (720 nm), but also fluorescence emission quenching (690 nm). With the ratiometric (A720/A677 for P-CfZnPc) absorption responses at two distinct wavelengths, absorption ratio increased as a linear function to the concentration of Be2+ in the range of 0.2 – 73 µM (2.03 – 739 ppb), and the detection limit was determined to be 8.4 x 10-8 M with very low response time less than 1 second. Also, fluorescence emission decreased as a linear function to the concentration of Be2+ in the range of 0.157 – 43 µM (1.617 – 439 ppb), and the detection limit was determined to be 7.7 x 10-7 M for fluorescence titration method less than 1 second.