| Schiff base complexes have been widely attentioned and have played an importantrole in many fields, due to their ligands the facile preparation and structural varieties.Their specific application fields are classified denpending on the nature of metal ionsand structure of ligand. Metals of IIB group have good fluorescence effect due to their dorbitals full-electronic structure. The complexes of these metals are usually in thesynthesis of fluorescent material. Therefore, in this thesis, three ligands are successfullysynthesized with the materils of6-methoxypyridine-2-carbaldehyde and1,3-diaminopropan-2-ol, benzene-1,3-diamine,4-methylbenzene-1,3-diamine,4-nitrobenzene-1,3-diamine. The four ligands are1,3-bis((6-methoxypyridin-2-yl)methyleneamino)propan-2-ol(L1), N,N’-bis((6-methoxypyridin-2-yl)methylene)benzene-1,3-diamine(L2), N,N’-bis((6-methoxypyridin-2-yl)methylene)-4-methyl-benzene-1,3-diamine(L3), N,N’-bis((6-methoxypyridin-2-yl)methylene)-4-nitrobenzene-1,3-diamine(L4). Then, five Schiff base complexes (Zn1, Cd1~Cd3, Hg1) aresysthesized with the ligands and IIB metal salts. On the other hand, an1D polymerchain complex(Cd4) is stepwise systhesized with2-acetylpyridine,1,3-phenylenediamine and Cd(NO3)2. After synthises, the10compounds structure arecharacterized by the way of NMR, IR and elemental analysis, in which L2, Cd2andCd3are obtained crystal structure. The fluorescence emission, lifetime and quantumyield of ligand and complexes are tested and discussed in the condition of solid stateand solution.Complexes’ fluorescence emission bands are narrower than which of ligands withthe monochromaticity increasing at the same time at298K in solid state. The band offlexible complexes (Zn1, Cd1, Hg1) exhibit a hypsochromic shift compared with L1.However, a bathochromic shift appears in rigid ligand (L2) and complexes (Cd2, Cd3).It is the result of ligand structure changed after coordination. The room temperature(298K) emission spectra of10complexes are recorded in different solvents (CH3CN,CH3OH, DMSO). Flexible complexs exhibit bathochromic shift in emission spectra assolvent polarity increases (polarity order: DMSO> CH3CN), characteristic of a largedipole moment upon excitation. Moreover, a blue shift is observed, thus indicating a reduction of the dipole moment upon electronic excitation. The photoluminescenceemission peaks of the Schiff bases apparently produce red shift with the introduction ofthe substituent. The reason is that the electron density of the phenyl ring is increasedwith the δâ†'Ï€ hyper conjugation effect. The fluorescence emission of Cd4is similar towhich of the flexible ligand (complexes). Dueing to the donor ability of CH3OH aspolar protic solvent, the hydrogen bond donor nature of CH3OH seems to stabilise thelarger poler state of the electronic transitions through solute–solvent interactions. Thelifetimes of10compounds belong to the microsecond scale. Furthermore, the lifetime isgreater impacted by the nature of the ligand and metal properties and the influence ofenvironment, and coordinating complexes have a longer fluorescence lifetime.The calculation results of quantum yield show that the complexes have strongerfluorescence emission than ligands. This is because the coordination of metal ionsincreases the rigidity of ligand, leading to a reduction of energy loss from excited stateto ground state, and also benefit to the Ï€ electron flowing. In conclusion, the10compounds can be used as potential of solvent and temperature sensitive fluorescentmaterial. |
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