Development of multi-functional Spin System by Combination of Photochromic Spin Coupler

用带有2，5-二(芳乙炔)-4-甲基-3-噻吩基侧基的二芳基乙烯证明了分子内磁性相互作用的光开关。在2，5-二(芳乙炔基)-4-甲基-3-噻吩基的两端各放置两个氮氧基。芳乙炔中含有3种芳基：2，5-亚硫基、对亚苯基和间亚苯基。二芳基乙烯光开关单元在二芳基乙烯的一侧具有延伸的π共轭链。光致变色反应活性依赖于芳乙炔基团。含间苯基的二芳基乙烯类化合物具有较好的光致变色反应活性。伴随着光致变色反应，二芳基乙烯的ESR谱发生了光开关，这是由于两个不成对的电子之间的磁相互作用发生了变化。开环异构体比光生闭环异构体表现出更强的交换作用。由于噻吩环2-位杂化轨道由sp2变为sp3，通过光环化改变了两个自由基间通过π共轭链的磁性相互作用。

Photoswitching of the intramolecular magnetic interaction was demonstrated using diarylethenes with 2,5-bis(arylethynyl)-4-methyl-3-thienyl side group. Two nitroxide radicals were placed at each end Of 2,5-bis(arylethynyl)-4-methyl-3-thienyl group. Three kinds of aryl groups, 2,5-thienylene, p-phenylene, and m-phenylene groups, were used in the arylethynyl moiety. The diarylethene photoswitching units have an extended π-conjugated chain on one side of the diarylethene. The photochromic reactivity was dependent on the arylethynyl group. Diarylethenes with m-phenylene group showed an efficient photochromic reactivity. Along with the photochromic reaction the diarylethenes showed photoswitching of ESR spectrum originating from the change in the magnetic interaction between two unpaired electrons. The open-ring isomer showed stronger exchange interaction than the photogenerated closed-ring isomer. The magnetic interaction between two radicals via the π-conjugated chain was altered by photocyclization due to the change of the hybrid orbital at the 2-position of the thiophene ring from sp2 to sp3.