Synthesis, structures and spectroscopic properties of new 1,2-bis[2-(4-methyl-7-acetylamino-1,8-naphthyridine)]ethylene ligand and its binuclear copper(I) complexes

• Published in: Inorganica Chimica Acta 2011-12, Vol.379 (1), p.7-15
• Main Authors: Li, Zhan-Xian, Li, Cong, Mu, Wei-Hua, Xiong, Shao-Xiang, Fu, Wen-Fu
• Format: Article
• Language: English
• Subjects: 1,8-Naphthyridine derivatives; Binuclear copper(I); Crystal structures; Spectroscopic properties; Vinyl
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2011.09.014

2-Bis[2-(4-methyl-7-acetylamino-1,8-naphthyridine)]ethylene and its binuclear copper(I) complexes with triphenylphosphine or bis(diphenylphosphino)methane are prepared and structurally characterized through single crystal X-ray diffraction, their spectroscopic properties including combined transient absorption and emission spectra are investigated. [Display omitted] ► 2-Bis[2-(4-methyl-7-acetylamino-1,8-naphthyridine)]ethylene is synthesized. ► Its binuclear copper(I) complexes with phosphine ligand are obtained. ► The complexes are structurally characterized through single crystal X-ray diffraction. ► Transient absorption and emission spectra of the compounds are also investigated. The synthesis, characterization, spectroscopic properties of a new ligand 1,2-bis[2-(4-methyl-7-acetylamino-1,8-naphthyridine)]ethylene ( L) and its two binuclear Cu(I) complexes containing triphenylphosphine (PPh 3) or bis(diphenylphosphino)methane (dppm), [Cu 2(L)(PPh 3) 4](BF 4) 2·2CH 2Cl 2 ( 1·2CH 2Cl 2) and [Cu 2(L)(dppm) 2](BF 4) 2·4H 2O ( 2·4H 2O) are reported. The structural investigation of these compounds based on X-ray crystal analysis shows that the copper(I) centers adopt different coordination geometries, O(N)CuP 2 + and NCuP 2 + for complexes 1 and 2, respectively. Upon irradiation of a degassed organic solution of L at 365 nm, photoinduced isomerization reaction and an intramolecular proton transfer of ligand L were detailed studied by absorption spectral changes. A spectroscopic investigation involving time-dependent density functional theory calculations allows assignment of the excited states that relate to emission and transient absorption spectra. The observed lower-energy absorption bands appearing in the region of 413 and 418 nm for 1 and 2 in dichloromethane are assigned to ligand-to-ligand charge transfer (LLCT, phosphine → napy) transition in nature. Compared with well-structured solid-state emission originating from ππ ∗ transition of ligand L, complexes 1 and 2 exhibit intense room-temperature solid-state emissions with λ max at 586 and 620 nm, respectively. The energy and the shape of the emission bands are clearly different from that of the ligand, indicating the emissions come from different excited states.