Separable syn/anti Bis-Boron Dyes with Stereochemistry-Dependent Packing and Aggregated-State Emission.

We report a new class of bis-boron fluorophores, BOSQUIs, accessible via a sequential multicomponent condensation/boron complexation strategy, and their syn/anti-stereoisomers can be directly observed and separated. These dyes display large Stokes shifts and tunable monomeric and aggregated-state emission governed by π-scaffold variation and axial aryl stereochemistry. The anti-3a further enables wash-free, high-contrast dynamic imaging and quantitative visualization of oleic-acid-induced lipid droplet biogenesis in living cells.