Green-Tuning of (Chir)Optical Properties for Axially-Chiral Boramidines

The integration of boron into π-conjugated systems is a reliable approach to enhance photophysical properties. In this context, boramidines have emerged as a promising class of fluorophores. In this work, the design, synthesis, and chiroptical properties of novel axially chiral isoquinoline-derived boramidines are reported. Thanks to metal-catalyzed cross-coupling allied with atroposelective C─H arylation strategies or chiral stationary phase HPLC resolution, enantioenriched boramidines 1 and 2 are afforded (ee 90%–99%). Comparing with more classical boramidines, investigations reveal (i) bathochromic absorption shifts in the UV–vis region (>50 nm) and (ii) emission maxima now in the green and cyan domains, along with fluorescence quantum yields reaching 70% in N₂-saturated environments. Chiroptical measurements demonstrate well-defined electronic circular dichroism (ECD) spectra and circularly polarized luminescence (CPL) signals with |g_lum| values up to 2 × 10⁻³.