Department of Chemistry, Shandong University, Jinan, China.
Photochem Photobiol Sci. 2011 Jun;10(6):1030-8. doi: 10.1039/c1pp00001b. Epub 2011 Mar 8.
A series of six Bodipy derivatives, namely 4,4-difluoro-8-(4-amidophenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (1), 4,4-difluoro-8-(4-methylphenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (2), 4,4-difluoro-8-(4-nitrylphenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (3), 4,4-difluoro-8-(4-amidophenyl)-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (4), 4,4-difluoro-8-(4-methylphenyl)-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (5), and 4,4-difluoro-8-(4-nitrylphenyl)-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (6) were structurally characterized by single crystal X-ray diffraction analysis. Two methyl substituents attached at C-1 and C-7 positions of boron-dipyrromethene (Bodipy) moiety in compounds 1-3 were revealed to prevent the free rotation of the benzene moiety, resulting in a molecular configuration with an almost orthogonal dihedral angle between the Bodipy and benzene moieties with the dihedral angle in the range of 81.14-88.56°. This is obviously different from that for 4-6 with a free-rotating benzene moiety relative to the Bodipy core due to the lack of two methyl substituents in the latter series of compounds, leading to an enhanced interaction between the Bodipy and benzene moieties for 4-6 in comparison with 1-3. The resulting larger HOMO-LUMO gap for 1-3 than 4-6 results in a blue-shifted absorption band for 1-3 relative to that for 4-6. Comparative studies over their fluorescence properties also disclose the blue-shifted fluorescence emission band and corresponding higher fluorescence quantum yield for 1-3 relative to those of 4-6, revealing the effect of molecular configuration on the spectroscopic properties of Bodipy derivatives. Comparison of the redox behaviors of these two series of Bodipy compounds provides additional support for this point. In addition, the electron-donating/withdrawing property of the para substituent of the benzene moiety was shown to exhibit a slight influence on the electronic absorption and fluorescence emission properties of the Bodipy compounds.
一系列六种 Bodipy 衍生物，即 4,4-二氟-8-(4-氨基苯基)-1,3,5,7-四甲基-4-硼-3a,4a-二氮杂-s-茚（1）、4,4-二氟-8-(4-甲基苯基）-1,3,5,7-四甲基-4-硼-3a,4a-二氮杂-s-茚（2）、4,4-二氟-8-(4-硝基苯基）-1,3,5,7-四甲基-4-硼-3a,4a-二氮杂-s-茚（3）、4,4-二氟-8-(4-氨基苯基）-3,5-二甲基-4-硼-3a,4a-二氮杂-s-茚（4）、4,4-二氟-8-(4-甲基苯基）-3,5-二甲基-4-硼-3a,4a-二氮杂-s-茚（5）和 4,4-二氟-8-(4-硝基苯基）-3,5-二甲基-4-硼-3a,4a-二氮杂-s-茚（6）通过单晶 X 射线衍射分析进行了结构表征。在化合物 1-3 中，硼二吡咯甲烷（Bodipy）部分的 C-1 和 C-7 位置上的两个甲基取代基被揭示可阻止苯环部分的自由旋转，导致 Bodipy 和苯环部分之间的分子构象几乎呈正交二面角，范围在 81.14-88.56°之间。这与化合物 4-6 明显不同，由于后一系列化合物中缺少两个甲基取代基，苯环部分相对于 Bodipy 核自由旋转，导致 4-6 与 1-3 相比，Bodipy 和苯环部分之间的相互作用增强。1-3 的 HOMO-LUMO 能隙大于 4-6，导致 1-3 的吸收带相对于 4-6 发生蓝移。对其荧光性质的比较研究也揭示了 1-3 的荧光发射带蓝移，相应的荧光量子产率高于 4-6，表明分子构象对 Bodipy 衍生物的光谱性质有影响。这两个系列 Bodipy 化合物的氧化还原行为的比较也为这一点提供了额外的支持。此外，苯环部分对位取代基的供电子/吸电子性质对 Bodipy 化合物的电子吸收和荧光发射性质表现出轻微影响。
