Studies On The Applications Of Novel Derivatives Of 1, 8-naphthyridine And Imidazole In Fluorescent Chemosensor And Functional Complexes

Four novel ligands were designed and synthesized with derivatives of 1,8-naphthyridine, imidazole and polypyridine based on the design principle of fluorescent chemosensor. Some interesting results were obtained by applying them in detection of metal ions and preparation of functional complexes.1. A novel flexible ligand bis(7-methyl-1,8-naphthyridine-2-ylamino)methane (L1) was firstly synthesized and its three intriguing structural Zn²⁺ complexes, [Zn2(L1)2(OH)](ClO4)3 (L1Zn1), [Zn4(L1)2(OAc)6(OH)2]·CH2Cl2 (L1Zn2·CH2Cl2) and [Zn5(L1)2(OAc)10]n·4nH2O (L1Zn3·4H2O), were also prepared and determined by X-ray crystallography. Studies of the spectroscopic properties of these compounds showed that they were potential blue light emitting materials. The investigated fluorescence properties of L1 associated with various metal ions showed that the fluorescence enhancement of L1 with Cd²⁺ was more sensitive than with other interfering cations.2. A new conjugation molecule L2, based on 2,4,5-triphenylimidazole and 6-phenyl-2,2'-bipyridine (HC^N^N), was synthesized in two steps. The molecule can recognize Fe³⁺ in mixed solvents (THF/H2O, 1/1, v/v) by the appearance of new emission bands at 416 and 442 nm which can be attributed to the emission of the newly formed L2-Fe³⁺ complex. The binding constant of the complex was calculated to be (6.6±0.4)×103 M-1. Competition experiments showed that L2 had good selectivity to Fe³⁺. It was proved that Fe³⁺ interacted with the triphenylimidazole unit by spectral experiments and theory calculation which demonstrated that the triphenylimidazole unit was the electron donor and the HC^N^N unit was the electron acceptor.3. A novel conjugation molecule, L3, based on 2,4,5-triphenylimidazole and 2,2':6',2''-terpyridine (N^N^N) was synthesized with a similar method to that of L2. It had a strong fluorescence in an aqueous solution of THF (50%) (λem = 480 nm,φf = 0.45). Investigated results indicated that only Fe²⁺ can change the solution color from light green to purple with a new absorption band at 575 nm. The results showed that L3 had potential application in detection of Fe²⁺.4. Complexes L2Pt and L3Pt were prepared by reacting Pt²⁺ with L2 and L3. The investigation of their spectroscopic properties and spectral responses to acid indicated that they could be potential luminescent sensors for acid. Spectra of L2Pt and L3Pt were sensitive to solvents. Compared with the ligands, strong ICT were observed in L2Pt and L3Pt which can be suppressed by the interaction of acid with the triphenylimidazole uint of L2Pt and L3Pt. In addition, MLCT was observed when the acid interacted with L3Pt.5. A new ligand, L4 with a flexible (-CH2-)6 spacer was prepared by EDC condensation based on derivatives of 2,4,5-triphenylimidazole. It had a strong fluorescence in DMF (λem = 442 nm,φf = 0.70). Investigated results revealed that only Hg²⁺ can significantly quench its fluorescence. L4 was therefore a potential Hg²⁺ fluorescent chemosensor.