The BODIPY scaffold as a core chromophore for extended, oligomeric, and helically chiral π-systems

在本项目中，我们将合成和研究基于BODIPY基序的新型荧光团。该小组之前的工作表明，可以使用简单的氧化反应来构建性能更好的低聚染料。在第一工作包中，使用被α-氨基取代的BODIPY，以便通过氮桥联的BODIPY二聚体通过布赫瓦尔德-哈特威格反应获得被α-氯取代的BODIPY。据说这些化合物在氧化条件下在β-位置上发生环关闭，形成桥联吡咯体系。以这种方式开发的策略将被扩展，以达到类似的低聚体系。不对称的BODIPY单体，一方面带有氯取代基，另一方面带有氨基取代基，在这里使用。线性和循环体系的形成是可以想象的，然后它们应该被氧化成完全共轭的π体系。作为直接氧化的替代，也有可能通过与β-位置上的醛反应来使体系变硬，这样在进一步氧化后，应该可以得到通过环状吡啶体系连接的BODIPY。我们将详细研究这些化合物的光物理和结构性质。第二个工作包涉及基于几个BODIPY亚基的螺旋π-体系的构建和光物理研究。分离成对映体或这种螺旋-手性化合物的对映选择性结构应该能够发射出具有较高GLUM值的圆偏振光(CPL)。该合成思想是基于首先生成带有桥联亚甲基单元的β连接的BODIPY低聚物。随后，氧化应通过剩余的自由β‘-位置进行，该位置生成桥接的五元环并形成CC键。这种特殊的几何排列应该可以提供构型稳定的螺旋分子，其组成最少为四个亚基。一种将硼中心的中心手性转变为螺旋手性的策略应该有助于以有针对性的方式产生P-螺旋或M-螺旋手性物种。此外，还将研究螺旋的去对称化，例如通过附加末端电子给体，是否通过电荷转移或FRET效应增加CPL效率。

In this project, novel fluorophores based on the BODIPY motif will be synthesized and investigated. Previous work by the group has shown that simple oxidation reactions can be used to construct oligomeric dyes with improved properties. Bridging ethano units or benzannulations were used.In a first work package, BODIPYs substituted by α-amino groups are to be used in order to obtain BODIPYs substituted with α-chlorine by means of the Buchwald-Hartwig reaction via nitrogen-bridged BODIPY dimers. These are said to undergo ring closure at the β-position under oxidative conditions to form the bridging pyrrole system. The strategy developed in this way is to be expanded in order to arrive at analogous oligomeric systems. Unsymmetrical BODIPY monomers, which carry a chlorine substituent on the one hand and an amino substituent on the other hand, are to be used here. The formation of linear as well as cyclic systems is conceivable, which should then be oxidized to fully conjugated π systems. As an alternative to direct oxidation, there is also the possibility of stiffening the system by reaction with aldehydes in the β-position, so that after further oxidation BODIPYs linked via annulated pyridine systems should be obtainable. The photophysical and structural properties of these compounds will be studied in detail.The second work package deals with the construction and photophysical investigation of helical π-systems based on several BODIPY subunits. A separation into enantiomers or an enantioselective construction of such helical-chiral compounds should make it possible to emit circularly polarized light (cpL) with comparatively high glum values. The synthetic idea is based on first generating β-linked BODIPY oligomers with a bridging methylene unit. Subsequently, an oxidation should take place via the remaining free β'-position, which generates a bridging five-membered ring with the formation of a C C bond. This special geometric arrangement should provide configurationally stable helical molecules from as little as four subunits. A strategy that transfers central chirality at the boron center into helical chirality should help to generate P- or M-helical chiral species in a targeted manner. In addition, it is to be investigated whether desymmetrization of the helix, e.g. by attaching a terminal electron donor, increases the cpL efficiency via charge transfer or FRET effects.