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X-ray structures,photophysical characterization,and computational analysis of geometrically constrained copper(I)--phenanthroline complexes
Authors:Cody John  Dennisson Jeanette  Gilmore Joshua  VanDerveer Donald G  Henary Maged M  Gabrielli Alan  Sherrill C David  Zhang Yiyun  Pan Chia-Pin  Burda Clemens  Fahrni Christoph J
Institution:School of Chemistry and Biochemistry, Georgia Institute of Technology, 770 State Street, Atlanta, Georgia 30332, USA.
Abstract:A series of three geometrically constrained C(2)-symmetric Cu(I) mono-phenanthroline complexes were characterized by X-ray structural analysis, and their photophysical properties were investigated by absorption and emission spectroscopy. Visible light excitation yielded metal-to-ligand charge-transfer (MLCT) excited states with luminescence lifetimes up to 155 ns. Ultrafast transient absorption spectroscopy provided further insights into the excited-state dynamics and suggests for all three complexes the formation of a phenanthroline radical anion. In agreement with electrochemical measurements, the data further indicate that coordinative rearrangements are involved in nonradiative deactivation of the excited states. According to time-dependent density functional theory calculations (B3LYP/6-31G), the major MLCT transitions are polarized along the C(2) axis of the complex and originate predominantly from the copper d(xz) 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 MLCT luminescence. The relationship between structural and photophysical data of the studied Cu(I) mono-phenanthroline complexes agrees well with current models describing the photophysics of the related Cu(I) bis-diimine complexes.
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