X-ray Structures, Photophysical Characterization, and Computational Analysis of Geometrically Constrained Copper(I)-Phenanthroline Complexes
文摘
A series of three geometrically constrained C2-symmetric Cu(I) mono-phenanthroline complexes were characterizedby X-ray structural analysis, and their photophysical properties were investigated by absorption and emissionspectroscopy. Visible light excitation yielded metal-to-ligand charge-transfer (MLCT) excited states with luminescencelifetimes up to 155 ns. Ultrafast transient absorption spectroscopy provided further insights into the excited-statedynamics and suggests for all three complexes the formation of a phenanthroline radical anion. In agreement withelectrochemical measurements, the data further indicate that coordinative rearrangements are involved in nonradiativedeactivation of the excited states. According to time-dependent density functional theory calculations (B3LYP/6-31G**), the major MLCT transitions are polarized along the C2 axis of the complex and originate predominantlyfrom the copper dxz orbital. The computational analysis identifies an excited-state manifold with a number of close-lying, potentially emissive triplet states and is in agreement with the multiexponential decay kinetics of the MLCTluminescence. The relationship between structural and photophysical data of the studied Cu(I) mono-phenanthrolinecomplexes agrees well with current models describing the photophysics of the related Cu(I) bis-diimine complexes.