Study on excited states of hexamethoxybenzene-NO+ charge-transfer complex: incorporation of excited radical cation

Study on excited states of hexamethoxybenzene-NO+ charge-transfer complex: incorporation of... A charge-transfer (CT) complex of NOBF4 and hexamethoxybenzene (HMB), which gives out HMB•+ as a “fluorescent radical cation probe,” upon one-electron oxidation, has been designed to explore the excited state dynamics of contact radical ion pairs by laser-induced fluorescence and femtosecond transient absorption spectroscopic techniques. The acetonitrile solution of the CT complex showed weak fluorescence with a similar spectrum to that observed for free excited HMB radical cation (HMB•+*), suggesting the formation of HMB•+* upon the one-photonic excitation of the CT complex. The laser-power dependence of the fluorescence intensity supported the one-photonic excitation event. We have also observed a short-lived transient species but no long-lived species by femtosecond laser flash photolysis of the CT complex. The lifetime (6.5 ps) was in good accordance with its fluorescence quantum yield (2.5 × 10−5) and was able to assign the transient species to the fluorescent state, an excited radical ion pair [HMB •+*/NO•]. All the events were completed within the inner sphere and the short lifetime of the transient species could be attributed to rapid back-electron transfer. It is concluded that the excited radical cation character in the excited state of the CT complex originates from the radical ion character in the CT complex in the ground state and that a relatively long lifetime of HMB•+* facilitates its observation even in the contact ion pair. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Research on Chemical Intermediates Springer Journals

Study on excited states of hexamethoxybenzene-NO+ charge-transfer complex: incorporation of excited radical cation

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Publisher
Springer Netherlands
Copyright
Copyright © 2012 by Springer Science+Business Media B.V.
Subject
Chemistry; Catalysis; Physical Chemistry; Inorganic Chemistry
ISSN
0922-6168
eISSN
1568-5675
D.O.I.
10.1007/s11164-012-0660-4
Publisher site
See Article on Publisher Site

Abstract

A charge-transfer (CT) complex of NOBF4 and hexamethoxybenzene (HMB), which gives out HMB•+ as a “fluorescent radical cation probe,” upon one-electron oxidation, has been designed to explore the excited state dynamics of contact radical ion pairs by laser-induced fluorescence and femtosecond transient absorption spectroscopic techniques. The acetonitrile solution of the CT complex showed weak fluorescence with a similar spectrum to that observed for free excited HMB radical cation (HMB•+*), suggesting the formation of HMB•+* upon the one-photonic excitation of the CT complex. The laser-power dependence of the fluorescence intensity supported the one-photonic excitation event. We have also observed a short-lived transient species but no long-lived species by femtosecond laser flash photolysis of the CT complex. The lifetime (6.5 ps) was in good accordance with its fluorescence quantum yield (2.5 × 10−5) and was able to assign the transient species to the fluorescent state, an excited radical ion pair [HMB •+*/NO•]. All the events were completed within the inner sphere and the short lifetime of the transient species could be attributed to rapid back-electron transfer. It is concluded that the excited radical cation character in the excited state of the CT complex originates from the radical ion character in the CT complex in the ground state and that a relatively long lifetime of HMB•+* facilitates its observation even in the contact ion pair.

Journal

Research on Chemical IntermediatesSpringer Journals

Published: Jul 5, 2012

References

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