Prompt and Delayed Electron Ejection from Photoexcited Aqueous Bromo- and Chlorocuprate(I) Complexes

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 1997-05, Vol.101 (20), p.3670-3676
• Main Authors: Stevenson, Kenneth L, Dhawale, Ravi S, Horváth, Attila, Horváth, Ottó
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp963349a

Two different routes for ejection of hydrated electrons by photoexcited CuCl2 - and CuCl3 2- have been observed:  (1) a prompt (i.e. within the 5-ns laser pulse width) ejection directly from the charge-transfer excited states (characterized as CTTS or Rydberg states), and (2) a delayed ejection, with lifetimes of up to 105 ns, from the triplet states of the two complexes. These two processes have rather high quantum yields:  0.30−0.40 for the prompt ejection and 0.25−0.33 for the delayed ejection for the chlorocuprate(I) complexes. The delayed ejection process is the primary decay route for the two triplet species, 3CuCl2 - and 3CuCl3 2-, which are formed by intersystem crossing from the charge-transfer excited states formed by absorption of light by the bis- and triscoordinated complexes in equilibrium in the ground state. Both of the chlorocuprate triplet excited states are weakly luminescent species. The triplet tris species, 3CuCl3 2-, has a strong absorption band at 390 nm (ε ≈ 27 000 M-1 cm-1), and the biscoordinated species, 3CuCl2 -, probably absorbs in the same region as well. Other intermediates such as Cu(0) complexes and Cl2 •- radicals have also been observed as decay products. Prompt and delayed electron ejection has also been observed in CuBr3 2- with quantum yields of 0.25 and 0.18, respectively. A mechanism that incorporates a triplet excited state equilibrium is invoked to account for these observations.