Ratera Imma, Ruiz-Molina Daniel, Vidal-Gancedo José, Novoa Juan J, Wurst Klaus, Letard Jean-François, Rovira Concepció, Veciana Jaume
Institut de Ciència de Materials de Barcelona (CSIC), Campus Universitari de Bellaterra, 08193-Cerdanyola, Spain.
Chemistry. 2004 Feb 6;10(3):603-16. doi: 10.1002/chem.200305194.
New ferrocenyl Schiff-base polychlorotriphenylmethyl radicals have been synthesized and characterized. The imino group of one such radical undergoes an irreversible trans to cis structural isomerization induced by light. Such photoinduced isomerization has been monitored by UV/Vis and ESR spectroscopy and also monitored by HPLC. ESR frozen solution experiments at low temperature revealed that the cis isomer dimerizes, showing a strong antiferromagnetic interaction. Although numerous photochromic supramolecular systems have been described, such a photoinduced self-assembly process represents the first example of a one-way photoswitchable magnetic system in which a conversion between a doublet and a singlet ground state species is promoted by a photoinduced dimerization process driven by the formation of hydrogen bonds. DFT calculations on the minimized structure and on the rotational barriers have been performed to establish the origin of such behavior. The effect of the substituents and the media polarity on the photoisomerization of this imine chromophore have also been studied. It has been observed that the efficiency of the process is markedly dependent on the presence and characteristics of electron-donor and electron-acceptor substituents of the ferrocenyl Schiff-base polychlorotriphenylmethyl radicals as well as on the polarity of the solvent.
新型二茂铁基席夫碱多氯三苯甲基自由基已被合成并表征。其中一种此类自由基的亚氨基会发生由光诱导的不可逆反式到顺式结构异构化。这种光诱导异构化已通过紫外可见光谱和电子自旋共振光谱进行监测，也通过高效液相色谱进行监测。低温下的电子自旋共振冷冻溶液实验表明，顺式异构体发生二聚化，表现出强烈的反铁磁相互作用。尽管已描述了许多光致变色超分子体系，但这种光诱导自组装过程代表了单向光开关磁系统的首个实例，其中通过氢键形成驱动的光诱导二聚化过程促进了双重态和单重态基态物种之间的转换。已对最小化结构和旋转势垒进行密度泛函理论计算，以确定这种行为的起源。还研究了取代基和介质极性对该亚胺发色团光异构化的影响。已观察到，该过程的效率明显取决于二茂铁基席夫碱多氯三苯甲基自由基的供电子和吸电子取代基的存在及特性以及溶剂的极性。
