Sakamoto Ryota, Kume Shoko, Sugimoto Manabu, Nishihara Hiroshi
Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
Chemistry. 2009;15(6):1429-39. doi: 10.1002/chem.200801593.
Azobenzene derivatives modified with dithiolato-bipyridine platinum(II) complexes were synthesized, revealing their highly extended photoresponses to the long wavelength region as well as unique photocontrollable tristability. The absorptions of trans-1 and trans-2 with one azobenzene group on the dithiolene and bipyridine ligands, respectively, cover the range from 300 to 700 nm. These absorptions are ascribed, by means of time-dependent (TD)DFT calculations, to transitions from dithiolene(pi) to bipyridine(pi*), namely, interligand charge transfer (CT), pi-pi*, and n-pi* transitions of the azobenzene unit, and pi-pi* transitions of the bipyridine ligand. In addition, only trans-1 shows distinctive electronic bands, assignable to transitions from the dithiolene(pi) to azobenzene(pi*), defined as intraligand CT. Complex 1 shows photoisomerization behavior opposite to that of azobenzene: trans-to-cis and cis-to-trans conversions proceed with 405 and 312 nm irradiation, which correspond to excitation with the intraligand CT, and pi-pi* bands of the azobenzene and bipyridine units, respectively. In contrast, complex 2 shows photoisomerization similar to that of azobenzene: trans-to-cis and cis-to-trans transformations occur with 365 and 405 nm irradiation, respectively. Irradiation at 578 nm, corresponding to excitation of the interligand CT transitions, results in cis-to-trans conversion of both 1 and 2, which is the longest wavelength ever reported to effect the photoisomerization of the azobenzene group. The absorption and photochromism of 4, which has azobenzene groups on both the dithiolato and bipyridine ligands, have characteristics quite similar to those of 1 and 2, which furnishes 4 with photocontrollable tristability in a single molecule using light at 365, 405, and 578 nm. We also clarified that 1 and 2 have high photoisomerization efficiencies, and good thermal stability of the cis forms. Complexes 3 and 5 have almost the identical photoresponse to those of their positional isomers, complexes 2 and 4.
合成了用二硫醇基联吡啶铂（II）配合物修饰的偶氮苯衍生物，揭示了它们对长波长区域具有高度扩展的光响应以及独特的光控三稳态。二硫烯和联吡啶配体上分别带有一个偶氮苯基团的反式-1和反式-2的吸收范围覆盖300至700nm。通过含时密度泛函理论（TD）DFT计算，这些吸收归因于从二硫烯（π）到联吡啶（π*）的跃迁，即配体间电荷转移（CT）、偶氮苯单元的π-π和n-π跃迁以及联吡啶配体的π-π跃迁。此外，只有反式-1显示出独特的电子能带，可归因于从二硫烯（π）到偶氮苯（π）的跃迁，定义为配体内CT。配合物1表现出与偶氮苯相反的光异构化行为：反式到顺式和顺式到反式的转化分别在405和312nm照射下进行，这分别对应于配体内CT激发以及偶氮苯和联吡啶单元的π-π*能带激发。相比之下，配合物2表现出与偶氮苯相似的光异构化：反式到顺式和顺式到反式的转变分别在365和405nm照射下发生。在578nm处的照射，对应于配体间CT跃迁的激发，导致1和2的顺式到反式转化，这是报道的影响偶氮苯基团光异构化的最长波长。二硫醇基和联吡啶配体上都带有偶氮苯基团的4的吸收和光致变色特性与1和2非常相似，这使得4在单个分子中利用365、405和578nm的光具有光控三稳态。我们还阐明了1和2具有高光异构化效率以及顺式形式良好的热稳定性。配合物3和5与其位置异构体配合物2和4具有几乎相同的光响应。
