Studies On The Synthesis,Crystal Structure And Properties Of A Salamo-type Small Molecule Chemosensor

With the development of sensors for recognizing biologically and environmentally heavy and transition metal?HTM? ions, great efforts have been devoted to the design and synthesis of HTM selective fluorescent sensors due to the high sensitivity and easy operability of fluorescent technique. Salen-type?including Salamo-type? compounds and their analogues are most versatile chelating ligands in inorganic and organometallic chemistry. Some of the metallosalen complexes have been of considerable interest due to their ubiquitous use in a variety of catalytic chemical transformations nonlinear optical materials, biological systems, building blocks for supramolecular structures and magnetic materials, and so forth, but as fluorescent sensors, it has been rarely reported. Herein we report three Salamo-type compounds which can be used as sensors for recognition of metal ions and the recognition mechanism of the sensors.Firstly, we have designed and synthesized a novel single-armed Salamo-type bisoximes?H₃L¹? which can be used as a sensor for relay recognition of Zn²⁺ and Cu²⁺. H₃L¹ displays highly selective and ratiometric recognition of Zn²⁺ through the enhancement of the fluorescence intensity, the resulted complex L1-Zn²⁺ behaves Cu²⁺ selectivity with fluorescence quenching via Zn²⁺ replacement. The detection limit of H₃L¹ to Zn²⁺ and L1-Zn²⁺ to Cu²⁺ are evaluated to be 5.13 × 10-7 M and 2.05 × 10-7 M, respectively. We analyzed the recognition mechanism and the fluorescence response mechanism of the complexes L1-Zn²⁺ and L1-Cu²⁺ to H+ and OH- ions through the structures of H₃L¹, L1-Zn²⁺ and L1-Cu²⁺, which have been determined by X-ray crystallographic analyses. H₃L¹ can act in three ways when the ions(?1? Zn²⁺, Cu²⁺,?2? Zn²⁺, H+ and OH-,?3? Cu²⁺, H+ and OH-) were added to the H₃L¹ solution in succession. Furthermore, the sensor will be improved to the ?real word‘ for ions recognition.Secondly, there are two positions having been substituted by chlorine atoms in the 3,5-dichlorosalicylaldehyde part of the structure of the sensor H₃L¹, resulting in the fluorescence quantum yield decreased. In addition, the reductions relate to the number and the location of chlorine atoms. In order to improve the fluorescence emission properties of the sensors, we synthesis a new sensor H₃L² which using 5-chlorosalicylaldehyde instead of 3,5-dichlorosalicylaldehyde part that decreased the number of chlorine atoms. H₃L² can also act as a sensor for relay recognition of Zn²⁺ and C u²⁺ with high selectivity and sensitivity. The complexes L2-Zn²⁺ and L2-Cu²⁺ behave successive sensing of H+ and OH-. The detection limit of H₃L² to Zn²⁺ and L2-Zn²⁺ to Cu²⁺ are evaluated to be 1.13 × 10-9 M and 2.05 × 10-7 M, respectively, with obvious improvement and improvement. It is more important that we improve the testing environment of sensor from organic solution to vivo system, which may provide the possibility for its application in environmental and life medicine.Finally, because of the substituents of both H₃L¹ and H₃L² are chlorine atoms, which are electrophilic groups and lead to the fluorescence emission decreased. In order to further improve the luminescence properties of the sensor, we introduce a new sensor based on the-OH group, which can enhance the fluorescence intensity of the H₄L³. H₄L³ can act as a fluorescent sensor for ratiometric recognition of Zn²⁺ with high selectivity and sensitivity in vivo. Furthermore, an obvious color change to pale pink between H₄L³ and Pb²⁺ can be visually observed by the naked eye in visible light. Crystallographic data of the HL3-Cu²⁺ reveals that the whole molecule forms a self assembled 2D supramolecular plane structure by hydrogen bonding interactions of C18-H18B···O1 and C15–H15A···Cg10. Perhaps as a Pb²⁺ fluorescent sensor, its performance is not so ideal and the recognition mechanism is also not very clear, however, a lot of inspiration will be provided for our further research on the ions recognition of Salamo-type sensors.