Red-Shifted Circularly Polarised Luminescence from Helically Chiral N,N,O,O-Boron Chelated Dipyrromethenes through Synthetically Facile meso-CF3 Modification

In the search for red-shifted small molecule emitters of circularly polarised light, a helically chiral N,N,O,O-boron chelated dipyrromethene (BODIPY) is described containing a meso-CF3 group, prepared in only two synthetic steps. The incorporation of an electron deficient substituent at the meso-position of a helically chiral BODIPY results in significant (~50 nm) red-shift of both the absorption (615 669 nm) and emission maxima (635 686 nm) in comparison to the parent compound, whilst maintaining a high extinction coefficient (83,000 mol-1 cm-1) and reasonable fluorescence quantum yield (0.30). Enantiomers were resolved by chiral stationary phase HPLC and absolute configuration assigned by the comparison of the experimental and calculated ECD spectra (gabs 3.6 × 10-3). A luminescence dissymmetry factor (glum 2.3 × 10-3) is reported, well supported by calculation (glum(calc) 2 × 10-3), resulting in an overall CPL brightness (BCPL = 29 M-1 cm-1) that is consummate with similar helically chiral monomeric BODIPYs. This work demonstrates the use electron deficient meso-CF3 groups in the development of red-shifted circularly polarised luminescent small organic molecules (CPL-SOMs), whilst maintaining their key chiroptical properties.