B₂N₂-Doped Dibenzo[a,m]Rubicene: Modular Synthesis, Properties, and Coordination-Induced Color Tunability

B2N2-doped dibenzo[a,m]rubicene (B2N2−DBR) and derivatives possessing two B–N units C2h-symmetrically on two edges are synthesized on a multigram scale via a two-step modular synthetic route using commercially available indole, aldehyde, and dichloroborane. Photophysical and electrochemical properties, crystal packing, and the reactivity of B2N2–DBR have been investigated. B2N2–DBR showed a larger optical gap and hence blue-shifted absorption and emission with a larger fluorescence quantum yield (Φ = 0.88) and a much smaller Stokes shift than its all-carbon analogue (DBR, Φ = 0.25). The blue-emissive B2N2–DBR derivatives are stable under ambient conditions against water and air but sensitive to nucleophiles such as fluoride and pyridine. B2N2–DBR reversibly interacts with a fluoride ion to bathochromically shift its emission with retention of a high fluorescence quantum yield, while coordination with pyridine quenches its photoluminescence. The marked changes in luminescence properties and optical gap on interaction with a Lewis base along with good chemical stability suggest the application of B2N2–DBR derivatives in colorimetric chemo- and biosensors.