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

摘要

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.