Fluorescent chiral molecules are capable of spontaneously emitting left or right-circularly polarised light, this is known as circularly polarised luminescence (CPL). From CPL we can garner information about the chirality of the molecule as well as the wavelength and intensity of the emitted light. Chiral lanthanide complexes are commonly used chiral probes for CPL, however they tend to have low fluorescence quantum yields. To achieve efficient CPL, a high quantum yield and a high | g lum | is required, so there is interest in developing small, organic molecules which display CPL and have high quantum yield and | g lum |. BODIPY dyes are small, fluorescent, organic molecules which generally have high quantum yield and strong UV absorption. This makes them ideal candidates for CPL-based sensing. However there are few dyes which are intrinsically chiral, requiring most to be conjugated with a chiral substituent, decreasing the quantum yield. Our synthesis pathway to our target BODIPY 4 involves the creation of a dipyrromethane via a condensation reaction between pyrrole and benzaldehyde. Subsequently the dipyrromethane is brominated, oxidised by DDQ and chelated by BF3.OEt2 to give our brominated intermediate 3. Helically chiral BODIPY 4 was then isolated from a Suzuki cross-coupling reaction. We propose that a possible mechanism for the formation of this unusual N,N,O,C-boron chelated dipyrromethene is due to the replacement of the central boron atom by the boronic acid, followed by a subsequent Suzuki coupling. In order to test the suitability of BODIPY 4 as a CPL probe, we resolved the enantiomers by semi-preparative chiral HPLC, and subsequently recorded the electronic circular dichroism (ECD) spectra. The CPL of this molecule was also measured and a reasonable glum value of 3.7 x 10-3 was recorded.

Synthesis of a novel chiral N,N,O,C-boron chelated dipyrromethene

256th National Meeting (2018)

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