Department of Chemistry and Molecular Biology, University of Gothenburg, Kemivägen 10, 41296 Gothenburg, Sweden.
J Org Chem. 2022 Mar 4;87(5):2569-2579. doi: 10.1021/acs.joc.1c02525. Epub 2022 Feb 21.
In the field of fluorescent dyes, difluoroboron-dipyrromethenes (BODIPY) have a highly respected position. To predict their photophysical properties prior to synthesis and therefore to successfully design molecules specifically for one's needs, a solid structure-function understanding based on experimental observations is vital. This work delivers a photophysical evaluation of BODIPY and aza-BODIPY derivatives equipped with different electron-withdrawing/-donating substituents. Using combinatorial chemistry, pyrroles substituted with electron-donating/-withdrawing substituents were condensed together in two different manners, thus providing two sets of molecules. The only difference between the two sets is the bridging unit providing a so far lacking comparison between BODIPYs and aza-BODIPYs structural homologues. Replacing the -methine bridge with an aza-N bridge results in a red-shifted transition and considerably different, temperature-activated, excited-state relaxation pathways. The effect of electron-donating units on the absorption but not emission for BODIPYs was suppressed compared to aza-BODIPYs. This result could be evident in a substitution pattern-dependent Stokes shift. The outlook of this study is a deeper understanding of the structure-optics relationship of the (aza)-BODIPY-dye class, leading to an improvement in the design of tailor-made molecules for future applications.
在荧光染料领域，二氟硼二吡咯（BODIPY）具有很高的地位。为了在合成前预测其光物理性质，从而成功地设计出专门满足特定需求的分子，基于实验观察的坚实的结构-功能理解至关重要。这项工作对带有不同吸电子/给电子取代基的 BODIPY 和氮杂 BODIPY 衍生物进行了光物理评估。使用组合化学，用吸电子/给电子取代基取代的吡咯以两种不同的方式缩合在一起，从而提供了两组分子。这两组分子之间的唯一区别是桥接单元，这为 BODIPY 和氮杂 BODIPY 结构类似物之间提供了迄今为止缺乏的比较。用氮杂-N 桥取代 -亚甲基桥会导致跃迁红移，并产生截然不同的、温度激活的、激发态弛豫途径。与氮杂 BODIPY 相比，供电子单元对 BODIPY 的吸收而不是发射的影响被抑制。与取代模式相关的斯托克斯位移的差异可以证明这一结果。本研究的展望是更深入地了解（氮杂）-BODIPY 染料类的结构-光学关系，从而改进未来应用中定制分子的设计。
