Jaska Cory A, Piers Warren E, McDonald Robert, Parvez Masood
Department of Chemistry, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, Canada.
J Org Chem. 2007 Jul 6;72(14):5234-43. doi: 10.1021/jo0706574. Epub 2007 Jun 12.
A series of planar and twisted heteroaromatic quaterphenyl analogues containing BN ring linkages has been synthesized using primarily difunctional Lewis acidic diborabiphenyl moieties as molecular cores. Crystal structure analyses indicated the presence of large twist angles between adjacent aromatic rings in 1 and 3, which were also observed to possess nonfluorescent behavior due to a lack of molecular rigidity and insufficient B=N character in the excited state. In contrast, the incorporation of one or two bridging ethylene groups between the adjacent rings (installed via an ethynyl cycloisomerization) was found to afford planar phenanthrene or pyrene moieties, which resulted in weak fluorescence behavior (Phi F = 0.02-0.16) for the n-Bu and Ph derivatives 5-12. Emission colors ranged from green (lambda em = 521 nm) to red (lambda em = 630 nm) and depended primarily on the conformation (2,2'- vs 4,4'-), the extent of chromophore conjugation (phenanthrene vs pyrene), and the type of exocyclic substituent present (n-Bu vs Ph). Communication between the two phenanthrene or pyrene moieties was observed in some cases, which was characterized by bathochromically shifted emission bands relative to that of monomeric phenanthrene or pyrene species. Unique excited-state dimer (excimer) fluorescence was observed for the 2,2'-isomer 8, which was characterized by broad, low-energy emission bands bathochromically shifted from that of the corresponding monomer.
一系列含有硼氮环连接的平面和扭曲的杂芳族四苯基类似物已被合成，主要使用双官能团的路易斯酸性二硼联苯部分作为分子核心。晶体结构分析表明，化合物1和3中相邻芳环之间存在较大的扭转角，由于缺乏分子刚性以及激发态下硼氮键特性不足，它们也表现出非荧光行为。相比之下，在相邻环之间引入一个或两个桥连乙烯基（通过乙炔环异构化引入）可得到平面菲或芘部分，这导致正丁基和苯基衍生物5 - 12呈现弱荧光行为（荧光量子产率(\varPhi_F) = 0.02 - 0.16）。发射颜色范围从绿色（(\lambda_{em}) = 521 nm）到红色（(\lambda_{em}) = 630 nm），主要取决于构象（2,2'- 对4,4'-）、发色团共轭程度（菲对芘）以及外环取代基的类型（正丁基对苯基）。在某些情况下观察到两个菲或芘部分之间存在相互作用，其特征是相对于单体菲或芘物种，发射带出现红移。对于2,2'-异构体8观察到独特的激发态二聚体（激基缔合物）荧光，其特征是宽的、低能量发射带相对于相应单体发生红移。
