2,2'-Disilylazobenzenes featuring double intramolecular nitrogen∙∙∙silicon coordination: a photoisomerizable fluorophore.
2,2'-Disilylazobenzenes featuring double intramolecular nitrogen∙∙∙silicon coordination: a photoisomerizable fluorophore.
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DOI：
10.1039/c5dt02038g
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发表时间：
2015-09
影响因子：
4
通讯作者：
N. Kano;M. Yamamura;T. Kawashima
中科院分区：
文献类型：
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作者：
N. Kano;M. Yamamura;T. Kawashima
(E)-4合成了4 '-二甲基-2，2'-二甲硅基偶氮苯。用X射线晶体学分析和（29）Si NMR谱证实了双（氟二甲基硅烷基）和双（三氟硅烷基）衍生物中的双分子内N-N-双-Si配位。在吸收带中，由于π，π* 跃迁，发现硅基的引入引起红移。与大多数根本不发荧光的偶氮苯相反，具有N-三氟甲硅烷基-Si配位的（E）-2，2 '-双（三氟甲硅烷基）偶氮苯衍生物在室温下发黄绿色荧光。甲基和三氟甲硅烷基基团降低了n和π* 轨道，如DFT计算所揭示的。结果表明，最低单重态激发能态是允许的π，π* 跃迁，而不是一般偶氮苯的禁戒的n，π* 跃迁.的最低单重激发态和适度刚性构象的偶氮部分，由双N-N-双-Si配位提供的允许的过渡字符，占的荧光发射。然而，N-二甲硅烷基-Si配位足够弱以在光激发时裂解，因此（E）-2，2 '-二甲硅烷基偶氮苯经历光异构化为（Z）-异构体。首次实现了偶氮苯部分的光致异构化和荧光发射性质。在（E）-2，2 '-二甲硅烷基偶氮苯光异构化为相应的（Z）-异构体后，它们不发荧光。光致异构化时荧光强度的这种变化对于荧光性质的调节是有用的。因此，该化合物可以被认为是一种独特的光致异构荧光团，可以使用单个光源调节荧光强度。
(E)-4,4'-Dimethyl-2,2'-disilylazobenzenes were synthesized. Double intramolecular N∙∙∙Si coordination in the bis(fluorodimethylsilyl) and bis(trifluorosilyl) derivatives was confirmed using X-ray crystallographic analysis and (29)Si NMR spectroscopy. In the absorption bands, due to the π,π* transitions, introduction of silyl groups was found to cause a bathochromic shift. In contrast to most azobenzenes, which do not fluoresce at all, the (E)-2,2'-bis(trifluorosilyl)azobenzene derivative with the N∙∙∙Si coordination fluoresced a yellow-green colour at room temperature. Methyl and trifluorosilyl groups lowered the n and π* orbitals, as revealed by DFT calculations. As a result, the lowest singlet excitation energy state is found to be the allowed π,π* transition, different from the forbidden n,π* transition in general azobenzenes, as revealed by TD-DFT calculations. The allowed transition character of the lowest singlet excited state and moderately rigid conformation of the azo moiety, provided by the double N∙∙∙Si coordination, account for the fluorescence emission. Nevertheless, the N∙∙∙Si coordination is weak enough to be cleaved upon photoexcitation, and thus the (E)-2,2'-disilylazobenzenes undergo photoisomerization to the (Z)-isomers. Both the photoisomerization and fluorescence emission properties of the azobenzene moiety have been achieved for the first time. After photoisomerization of the (E)-2,2'-disilylazobenzenes to the corresponding (Z)-isomer, they do not fluoresce. This change in the fluorescence intensity upon photoisomerization is useful for the regulation of fluorescence properties. Therefore, this compound can be recognized as a unique photoisomerizable fluorophore to regulate the fluorescence intensity using a single light source.