Department of Chemistry, University of Science and Technology Beijing, Beijing 100083, China.
J Org Chem. 2011 May 20;76(10):3774-81. doi: 10.1021/jo200050a. Epub 2011 Apr 15.
A series of four novel 8-hydroxyquinoline-substituted boron-dipyrromethene derivatives, namely 4,4-difluoro-8-(5-(8-hydroxyquinoline))-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (1), 4,4-difluoro-8-(5-(8-hydroxyquinoline))-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (2), 4,4-difluoro-8-(5-azastyryl-(8-hydroxyquinoline))-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (3), and 4,4-difluoro-8-(5-azastyryl-(8-hydroxyquinoline))-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (4), have been synthesized and characterized by a series of spectroscopic methods. The molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction analyses. The two methyl substituents attached at C-1 and C-7 positions of boron-dipyrromethene (Bodipy) in compound 2 was revealed to prevent the free rotation of the 8-hydroxyquinoline (8-HQ) moiety, resulting in an almost vertical 8-HQ-Bodipy configuration of this compound. This is obviously different from those for 1 with the dihedral angle between 8-hydroxyquinoline and Bodipy moieties of 65.44 and 66.79° due to the lack of methyl substituents in the latter compound. The intense fluorescence from the Bodipy subunit of these compounds was revealed to gradually get diminished along with either decreasing or increasing the pH value under acidic and basic conditions, respectively, in particular for 1, 2, and 4 because of the photoinduced intramolecular electron transfer from excited Bodipy moiety to 8-HQ unit and just an opposite process. This renders these compounds the first OFF-ON-OFF type of pH-dependent fluorescent sensors. Nevertheless, both the intrinsic fluorescence of these compounds and their fluorescent quenching properties along with the change in the pH value have been found to depend on the steric configuration as well as the linking group between 8-hydroxyquinoline and Bodipy moieties, revealing the effect of molecular structure on their fluorescence properties.
一系列四个新型 8-羟基喹啉取代硼二吡咯甲烷衍生物，即 4,4-二氟-8-(5-(8-羟基喹啉))-3,5-二甲基-4-硼-3a,4a-二氮杂-s-茚并[1,2-b]吡咯（1），4,4-二氟-8-(5-(8-羟基喹啉))-1,3,5,7-四甲基-4-硼-3a,4a-二氮杂-s-茚并[1,2-b]吡咯（2），4,4-二氟-8-(5-(5-氮杂二苯并噻吩基-8-羟基喹啉))-3,5-二甲基-4-硼-3a,4a-二氮杂-s-茚并[1,2-b]吡咯（3）和 4,4-二氟-8-(5-(5-氮杂二苯并噻吩基-8-羟基喹啉))-1,3,5,7-四甲基-4-硼-3a,4a-二氮杂-s-茚并[1,2-b]吡咯（4）已经通过一系列光谱方法合成并表征。通过单晶 X 射线衍射分析确定了 1 和 2 的分子结构。化合物 2 中硼二吡咯（Bodipy）上 C-1 和 C-7 位置的两个甲基取代基被揭示可阻止 8-羟基喹啉（8-HQ）部分的自由旋转，导致该化合物的 8-HQ-Bodipy 构象几乎垂直。这与后者化合物的 8-羟基喹啉和 Bodipy 部分之间的二面角为 65.44 和 66.79°明显不同，因为后者化合物中没有甲基取代基。这些化合物的 Bodipy 亚基的强烈荧光被揭示随着酸性和碱性条件下 pH 值的降低或升高而逐渐减弱，特别是对于 1、2 和 4，因为从激发的 Bodipy 部分到 8-HQ 单元的光诱导分子内电子转移以及正好相反的过程。这使这些化合物成为第一类 pH 依赖性荧光传感器的 OFF-ON-OFF 型。然而，这些化合物的固有荧光及其荧光猝灭特性以及 pH 值的变化都发现依赖于立体构型以及 8-羟基喹啉和 Bodipy 部分之间的连接基团，揭示了分子结构对其荧光性质的影响。
