二杂芳基乙烯光二聚反应与二聚体的晶体结构

通过反-1,2-双(2-苯并唑基)乙烯(BBE)和反-1-(2-苯并咪唑基)-2-(2-苯并唑基)乙烯(BME)的光二聚反应合成了r-1,c-2,t-3,t-4-四(2-苯并唑基)环丁烷(BBC)和r-1,c-2,t-3,t-4-1,3-双(2-苯并咪唑基)-2,4-双(2-苯并唑基)环丁烷(BMC).用元素分析、红外、紫外、核磁共振谱、质谱及X射线衍射表征了二聚体的结构.BBC晶体属三斜晶系,空间群为P1.晶胞参数:a=0.64684(13)nm,b=1.3242(3)nm,c=1.6245(3)nm;α=74.66(3)°,β=78.77(3)°,γ=76.06(3)°,Z=2.BBC晶胞中分子有两种取向,两种取向不同分子的苯并唑平面间存在着π-堆积现象.π-堆积面间的距离在0.330～0.376nm之间,与石墨晶体中分子平面片层间的距离非常接近.BBC和BMC都具有中心对称性,光二聚反应的高度立体选择性以及BBE和BME的光二聚反应不受空气中氧的影响的事实表明它们是经激发单线态历程以面对面的方式进行二聚反应的,本文检测到了BBE和BME在高浓度溶液中的激基缔合物荧光.

Photodimerization of Heteroarylethenes and Crystal Structure of the Photodimers

r-1,c-2,t-3,t-4 Tetra(2-benzoxazolyl)cyclobutane(BBC) and r-1,c-2,t-3,t-4 bis(2-benzimidazolyl)-2,4-bis(2-benzoxazolyl)cyclobutane(BMC) were synthesized with a high stereoselectivity by the photodimerization of trans 1,2-bis(2-benzoxazolyl)ethene and trans-1-(2-benzimidazolyl)-2-(2-benzoxazolyl)ethene respectively. The structures of BBCand BMCwere identified by elemental analysis, IR, UV, ¹H NMR, ¹³C NMR, MSas well as X-ray diffraction method. The crystal of BBCis triclinic, space group: P1. Unit cell parameters: a = 0. 64684 (13) nm, b = 1. 3242(3) nm, c = 1.6245(3) nm; α= 74. 66(3)° , β= 78.77(3)°, γ= 76.06(3)°, V = 1.2896(4) nm³ , Z=2, Dc= 1.351 g·cm^-1 . There are two kinds of molecules with the same stereostructure but different orientations in the crystal cells. The π-stacking between the benzoxazolyl planes of different molecules was found. The distance of the π-stacking planes is 0.330 ～ 0.376 nm, quite similar with that of graphite(0.335 nm). Both of BBCand BMChave head to tail configuration. It was found that the dimerization benefit by increasing the polarity of the solvents and increasing the conjugate system. The photodimerization has a high stereoselectivity and isn't affected by the presence of oxygen, which demonstrated the reaction proceeding through an excited singlet state. The excimer fluoresence of BBCand BMCwas detected.