1, 8-Naphthyridine-based D～(10) Complexes: Synthesis, Structures And Photophysical Proprerties

Copper(I) complexes have attracted most attention for their diverse structures and rich photophysical properties. The usual coordination geometries of CuI center are line, planar trigon or tetrahedron with the coordination number from 2 to 4. Depending on the nature of ligand, MLCT, LMCT, LLCT, or MC transition can be the lowest energy electronic excited state. Therefore it is very important for the application of these copper(I) complexes to investigate the relation between molecular structures and the excited state, and the effects of metal-metal and metal-anion/solvent weak interaction on spectroscopic properties. 1,8-naphthyridine and its derivatives, which provided two nitrogen atoms seperated for 2.307 ?, are quite useful bidentate ligands and can act as a (i) monodentate, (ii) bidentate and (iii) dinuclear bridging ligands. In particular, the bridging ligand mode provides a variety of interesting polynuclear structures with a short metal-metal distances. In this dissertation, four novel 1,8-naphthyridine derivatives and nine copper complexes as well as five zinc complexes containing these ligands were synthesized and structurally characterized by X-ray crystal analysis. Some interesting results were obtained from these structural and spectroscopic investigations.1. The single crystal structure of L2 shows that two naphthyridine rings are near co-planar, resulting in the interaction between them through amino bridge. To the best of our knowledge, this is the first naphthyridine-based compound displaying both dual emission and two groups of structured absorptions. The dual fluorescence emissions of L2, which depend on the properties of solvents and excitation energy, are attributed to molecular conformational equilibrium in the ground state, which are different from those in the cases of TICT and EXPT.2. A series of mono-, dinuclear and tetranuclear copper(I) complexes were prepared by reacting [Cu(CH3CN)4]BF4 with phosphine and 1,8-naphthyridine-based ligands via varied molar ratio, some of which exhibit 3MLCT emission and high-emission quantum yield and long lifetime in the fluid solution at room temperature. Especially, tetranuclear copper(I) complexes Cu-8 and Cu-9 with microsecond scale of emission lifetimes are very stable upon atmosphere and irradiation, and their emission quantum yields are nearly forty times of those of dinuclear ones. The results suggest that close CuI···CuI contacts in polynuclear complexes play key roles in enhancing stability and affecting photophysical properties.3. A series of neutral and ionic zinc(II) complexes were obtained from reactions of 1,8-naphthyridine derivatives with Zn(OAc)2, ZnCl2 or Zn(ClO4)2. Depending on the anions, these complexes were self-assembled to form molecular pairs or lines in the solid state via intramolecur or intermolecular hydrogen bonds, which further formed sheets or network through aromaticπ-πstacking interactions.