Investigation of the structural, optical, and electrochemical properties of a BODIPY system functionalized with carbazole and bromine moieties

In this study, a novel tetrabromo-substituted BODIPY derivative containing a carbazole unit (Br₄-CB) was synthesized, and its structural, photophysical, and electrochemical properties were thoroughly investigated. Single-crystal X-ray diffraction analysis revealed a molecular architecture stabilized by halogen–halogen interactions, featuring extended π-conjugation and pronounced intermolecular π–π stacking. Optical measurements conducted in various solvents showed strong absorption and emission characteristics, high fluorescence quantum yields reaching up to 0.98 in hexane, and significant solvent-dependent Stokes shifts. Br₄-CB exhibited a singlet oxygen quantum yield (Φ_Δ) of 0.50 in DMSO. Furthermore, efficient energy transfer from the carbazole moiety to the BODIPY core was observed in DCM, as confirmed by fluorescence measurements, accompanied by a notably prolonged fluorescence lifetime compared to other solvents (τ = 12.9 ns). Electrochemical analyses and DFT calculations revealed consistent HOMO-LUMO energy levels and a narrow bandgap (E_gap = 1.37–1.40 eV), highlighting the compound's potential as a semiconducting material. Overall, the synergistic effect of the carbazole and bromine functionalities effectively modulates the physicochemical behavior of the BODIPY framework, positioning Br₄-CB as a promising core structure for light-harvesting applications.