Photoinduced Radical Formation from the Complexes [Re(R)(CO)3(4,4'-Me2-bpy)] (R = CH3, CD3, Et, iPr, Bz): A Nanosecond Time-Resolved Emiss
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- 作者：Cornelis J. Kleverlaan ; Derk J. Stufkens ; Ian P. Clark ; Michael W. George ; James J. Turner ; Dé ; bora M. Martino ; Hans van Willigen ; and Antoní ; n Vl
//pubs.acs.org/images/entit
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：October 28, 1998
- 年：1998
- 卷：120
- 期：42
- 页码：10871 - 10879
- 全文大小：128K
- 年卷期：v.120,no.42(October 28, 1998)
- ISSN：1520-5126
文摘
Irradiation of the complexes [Re(R)(CO)3(dmb)] (R = CH3, CD3, Et, iPr, or Bz; dmb = 4,4'-dimethyl-2,2'-bipyridine) into their visible absorption band gives rise to a homolytic cleavage of the Re-R bond withformation of the radicals [Re(CO)3(dmb)]
and R. In the case of R = Et, iPr, or Bz this reaction proceedswith unit efficiency. The nanosecond time-resolved absorption (TA) spectra show that the long-lived (
= 7
s) [Re(CO)3(dmb)] radicals are formed within the 7 ns laser pulse. The CH3 complex photodecomposeswith a quantum yield of only 0.4. The time-resolved UV-vis and IR absorption spectra reveal that this complex,after excitation into a 1MLCT state, may either pass a barrier of 1560 cm-1 to the dissociative 3
* state anddecompose into radicals or decay to the ground state via an excited-state having predominant 3MLCT statecharacter. Qualitative potential energy diagrams are presented for the two types of complexes. In a glass at80 K and in a low-temperature solution (T < 195 K), the methyl complex is photostable, and this allowed usto study its excited-state properties with time-resolved absorption, emission, and IR spectroscopies. Accordingto these spectra the lowest-excited 3MLCT state has a significant admixture of a * character. Finally,nanosecond time-resolved FT-EPR spectra were recorded of the CH3 and CD3 radicals produced by irradiationof [Re(CH3/CD3)(CO)3(dmb)]. The spectra of the CH3 radical exhibit a pronounced low-field emission/high-field absorption pattern due to an ST0 radical pair mechanism (RPM) CIDEP effect. The occurrence of thisST0 RPM confirms that the radicals are formed from an excited state, having spin-triplet character, in agreementwith the proposed mechanism involving a reactive 3* state.
and R. In the case of R = Et, iPr, or Bz this reaction proceedswith unit efficiency. The nanosecond time-resolved absorption (TA) spectra show that the long-lived ( = 7s) [Re(CO)3(dmb)] radicals are formed within the 7 ns laser pulse. The CH3 complex photodecomposeswith a quantum yield of only 0.4. The time-resolved UV-vis and IR absorption spectra reveal that this complex,after excitation into a 1MLCT state, may either pass a barrier of 1560 cm-1 to the dissociative 3* state anddecompose into radicals or decay to the ground state via an excited-state having predominant 3MLCT statecharacter. Qualitative potential energy diagrams are presented for the two types of complexes. In a glass at80 K and in a low-temperature solution (T < 195 K), the methyl complex is photostable, and this allowed usto study its excited-state properties with time-resolved absorption, emission, and IR spectroscopies. Accordingto these spectra the lowest-excited 3MLCT state has a significant admixture of a * character. Finally,nanosecond time-resolved FT-EPR spectra were recorded of the CH3 and CD3 radicals produced by irradiationof [Re(CH3/CD3)(CO)3(dmb)]. The spectra of the CH3 radical exhibit a pronounced low-field emission/high-field absorption pattern due to an ST0 radical pair mechanism (RPM) CIDEP effect. The occurrence of thisST0 RPM confirms that the radicals are formed from an excited state, having spin-triplet character, in agreementwith the proposed mechanism involving a reactive 3* state.© 2004-2018 中国地质图书馆版权所有 京ICP备05064691号 京公网安备11010802017129号 地址：北京市海淀区学院路29号 邮编：100083 电话：办公室：(+86 10)66554848；文献借阅、咨询服务、科技查新：66554700 |