UV-Vis, NMR, and time-resolved spectroscopy analysis of photoisomerization behavior of three- and six-azobenzene-bound tris(bipyridine)cobalt complexes.
UV-Vis, NMR, and time-resolved spectroscopy analysis of photoisomerization behavior of three- and six-azobenzene-bound tris(bipyridine)cobalt complexes.
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DOI：
10.1021/ic0513538
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发表时间：
2005-10
影响因子：
4.6
通讯作者：
Kyoko Yamaguchi;S. Kume;K. Namiki;Masaki Murata;N. Tamai;H. Nishihara
中科院分区：
文献类型：
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作者：
Kyoko Yamaguchi;S. Kume;K. Namiki;Masaki Murata;N. Tamai;H. Nishihara
tris的光异构化性质含六个或三个偶氮苯部分的（联吡啶）钴配合物，即[Co（II）（dmAB）3]（BF 4）2 [dmAB = 4，4 '-双[3“-（4“"-甲苯偶氮）苯基]-2，2 '-联吡啶]、[Co（III）（dmAB）3]（BF 4）3、[Co（II）（mAB）3]（BF 4）2 [mAB = 4-[3”"-（4“”-甲苯偶氮）苯基]-2，2“-联吡啶]和[Co（III）（dmAB）3]（BF 4）3，它们是由偶氮苯聚集在一个分子中的效应和钴（II）或钴（III）离子的效应产生的。在这四种配合物的光稳定状态下，Co（II）配合物中近50%的反式偶氮苯部分转化为顺式异构体，Co（III）配合物中近10%的反式偶氮苯部分异构化为顺式异构体，这意味着在365 nm下照射时处于光稳定状态的顺式异构体比率不受一个中偶氮苯部分的数目控制分子，而是由钴离子的氧化态。飞秒瞬态吸收光谱的配体和配合物表明，在Co（III）配合物中的偶氮苯部分的光激发态强烈失活的偶氮苯部分的钴中心，形成一个偶氮苯自由基阳离子和Co（II）中心的电子转移。用~ 1H NMR研究了[Co（II）（dmAB）_3]（BF_4）_2中6个偶氮苯基团的光化学结构变化之间的协同作用。甲基质子的1H NMR信号的时程变化表明，[Co（II）（dmAB）3]（BF 4）2中的每个偶氮苯部分异构化为顺式异构体，其随机概率为50%，并且偶氮苯部分之间没有相互作用。
The photoisomerization properties of tris(bipyridine)cobalt complexes containing six or three azobenzene moieties, namely, [Co(II)(dmAB)3](BF4)2 [dmAB = 4,4'-bis[3''-(4'''-tolylazo)phenyl]-2,2'-bipyridine], [Co(III)(dmAB)3](BF4)3, [Co(II)(mAB)3](BF4)2 [mAB = 4-[3' '-(4' ''-tolylazo)phenyl]-2,2'-bipyridine], and [Co(III)(dmAB)3](BF4)3, derived from the effect of gathering azobenzenes in one molecule and the effect of the cobalt(II) or cobalt(III) ion were investigated using UV-vis absorption spectroscopy, femtosecond transient spectroscopy, and 1H NMR spectroscopy. In the photostationary state of these four complexes, nearly 50% of the trans-azobenzene moieties of the Co(II) complexes were converted to the cis isomer, and nearly 10% of the trans-azobenzene moieties of the Co(III) complexes isomerized to the cis isomer, implying that the cis isomer ratio in the photostationary state upon irradiation at 365 nm is controlled not by the number of azobenzene moieties in one molecule but rather by the oxidation state of the cobalt ions. The femtosecond transient absorption spectra of the ligands and the complexes suggested that the photoexcited states of the azobenzene moieties in the Co(III) complexes were strongly deactivated by electron transfer from the azobenzene moiety to the cobalt center to form an azobenzene radical cation and a Co(II) center. The cooperation among the photochemical structural changes of six azobenzene moieties in [Co(II)(dmAB)3](BF4)2 was investigated with 1H NMR spectroscopy. The time-course change in the 1H NMR signals of the methyl protons indicated that each azobenzene moiety in [Co(II)(dmAB)3](BF4)2 isomerized to a cis isomer with a random probability of 50% and without interactions among the azobenzene moieties.