Photochemistry of monochloro complexes of copper(II) in methanol probed by ultrafast transient absorption spectroscopy |
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Authors: | Mereshchenko Andrey S Pal Suman K Karabaeva Kanykey E El-Khoury Patrick Z Tarnovsky Alexander N |
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Institution: | Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA. |
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Abstract: | Ultrafast transient absorption spectra in the deep to near UV range (212-384 nm) were measured for the Cu(II)(MeOH)(5)Cl](+) complexes in methanol following 255-nm excitation of the complex into the ligand-to-metal charge-transfer excited state. The electronically excited complex undergoes sub-200 fs radiationless decay, predominantly via back electron transfer, to the hot electronic ground state followed by fast vibrational relaxation on a 0.4-4 ps time scale. A minor photochemical channel is Cu-Cl bond dissociation, leading to the reduction of copper(II) to copper(I) and the formation of MeOH·Cl charge-transfer complexes. The depletion of ground-state Cu(II)(MeOH)(5)Cl](+) perturbs the equilibrium between several forms of copper(II) complexes present in solution. Complete re-equilibration between Cu(II)(MeOH)(5)Cl](+) and Cu(II)(MeOH)(4)Cl(2)] is established on a 10-500 ps time scale, slower than methanol diffusion, suggesting that the involved ligand exchange mechanism is dissociative. |
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