Creation of Chiral Organic Photochromic Dyes Applicable to Ultra-high Density Optical Memory System

二芳基乙烯是热不可逆光致变色化合物的代表性家族之一，当二芳基乙烯光化学环化时，产生两个立体碳原子。当不对称碳原子被引入到己三烯部分的邻居时，由于非对映选择性光致变色性，由环化产生的立体中心的绝对立体化学将变得高度偏向。我们已经合成了在己三烯部分末端具有不对称碳原子的化合物1，其表现出88 - 94%de的高非对映选择性光致变色闭环反应，通过应用烯丙基1，3-应变作为基态构象的立体控制的先导。然而，当连接苯并噻吩环和六氟环戊烯环的碳原子从苯并噻吩的C-3变为C-2时，尽管化合物（2）的比旋光度的变化大至1300度，但环闭合的非对映选择性下降至仅47%。我们设计并合成了化合物3，由于化合物1具有较大的电子排斥作用，而化合物2不具有较大的电子排斥作用，因此化合物3具有较高的非对映选择性。结果表明，3的光化学闭环反应的非对映选择性提高到90%。比旋光度的变化为953度。当手性先导取代基连接到两个苯并噻吩基乙烯上时，非对映选择性（4）高达98%，比旋度的变化为1429度。不幸的是，双萘并噻吩基乙烯5和具有苯并噻吩基和萘并噻吩基环的化合物6在UV照射下不能充分地得到环化化合物。

When diarylethenes, one of the representative thermally irreversible photochromic families, cylclize photochemically, two stereogenic carbon atoms are produced. When an asymmetric carbon atom is introduced to the neighbor of the hexatriene moiety, the absolute stereochemistry of the stereogenic centers generated by cyclization will become highly biased as the result of the diastereoselective photochromism. We have already synthesized compound 1 possessing an asymmetric carbon atom at the end of the hexatriene moiety, which showed such a high diastereoselective photochromic ring-closing reaction of 88 - 94% de, by applying allylic 1,3-strain as the pilot of the stereocontrol of the ground-state conformations. However, when the carbon atom connecting the benzothienyl ring and hexafluorocyclopentene ring was changed from C-3 of benzothiophene to C-2, the diastereoselectivity of the ring closure dropped to only 47%, though the change in specific optical rotation of the compound (2) was as large as 1300 degrees. We designed and synthesized compound 3 which should exhibit higher diastereoselectivity due to the larger electronic repulsion which was present in 1 but absent in 2. As the result, the diastereoselectivity of photochemical ring closure of 3 raised to 90%. The change in specific optical rotation was 953 degrees. These results were published in J. Org. Chem.When the chiral pilot substituent was attached to both of the benzothienylethenes, the diastereoselectivity (4) was as high as 98% and the change in specific optical rotation was 1429 degrees. Unfortunately, bisnaphthothienylethene 5 and the compound 6 with benzothienyl and naphthothienyl rings did not give the cyclized compound sufficiently upon UV irradiation.