Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
Molecules. 2023 Mar 23;28(7):2896. doi: 10.3390/molecules28072896.
Development of organic fluorophore is an important theme. Especially, the fluorophores with longer fluorescence peaks are useful to biological probes. One of the methods to change the fluorescence peak is the introduction of substituents. However, opposing characteristics of the substituents lead to different changes in the fluorescence peaks. Furthermore, the introduction of the substituent also affects their electric properties. Thus, if the materials were developed with the substituent effect on the optical and electric properties separately, it will be useful to design the functional materials related to both optical and electric properties. Herein, we investigated the substituent effect of dipyrrolo[1,2-:2',1'-]quinoxalines on fluorescence properties. We synthesized the compounds bearing electron-donating or electron-withdrawing substituents at the benzene ring on dipyrrolo[1,2-:2',1'-]quinoxaline, which would have more direct influence on the optical properties. By introducing each substituent at the 6 position of dipyrrolo[1,2-:2',1'-]quinoxaline, the bathochromic shift was observed in the fluorescence spectra. In the case of fluorine substituent, the change of the fluorescence peak reached was about 19 nm. Using a TDDFT calculation, we explained the reason for such a substituent effect that large on the increment of LUMO energy or decrement of HOMO energy occurred by introducing electron-withdrawing or electron-donating substituents at the 6 position, respectively. The substituent effect on the change of orbital energies is typical although the different characteristics of substituents resulted in the similar tendency about the change of fluorescence peak. Furthermore, with the introduction of phenyl substituents at the 3 and 10 positions, we achieved 40-50 nm longer fluorescence peaks compared with that of the original dipyrrolo[1,2-:2',1'-]quinoxaline.
有机荧光团的发展是一个重要的主题。特别是，荧光峰较长的荧光团对于生物探针很有用。改变荧光峰的一种方法是引入取代基。然而，取代基的相反特性导致荧光峰的不同变化。此外，取代基的引入也会影响其电性质。因此，如果将取代基对光学和电学性质的影响分别应用于材料的开发，这将有助于设计与光学和电学性质相关的功能材料。在这里，我们研究了二吡咯并[1,2-:2',1'-]喹喔啉上取代基对荧光性质的影响。我们合成了在二吡咯并[1,2-:2',1'-]喹喔啉苯环上带有供电子或吸电子取代基的化合物，这些取代基对光学性质有更直接的影响。通过在二吡咯并[1,2-:2',1'-]喹喔啉的 6 位上引入每个取代基，观察到荧光光谱的红移。在氟取代的情况下，荧光峰的变化达到了约 19nm。通过 TDDFT 计算，我们解释了这种取代基效应的原因，即在 6 位上引入吸电子或供电子取代基，分别导致 LUMO 能量的大幅增加或 HOMO 能量的大幅降低。尽管取代基的不同特性导致荧光峰变化的趋势相似，但取代基对轨道能变化的影响是典型的。此外，通过在 3 位和 10 位上引入苯基取代基，与原始二吡咯并[1,2-:2',1'-]喹喔啉相比，我们实现了 40-50nm 更长的荧光峰。
