A one-pot strategy to β-β methylene-bridged BODIPY oligomers with pronounced exciton coupling

BODIPY (boron dipyrromethenes) dyes serve as versatile platforms for optoelectronic and biomedical applications, owing to their outstanding photophysical properties and structural adaptability. Constructing BODIPY oligomers presents a powerful strategy to modulate their optical and electrochemical behavior through strong exciton coupling among chromophores. However, conventional synthetic routes, particularly for sp 3 -carbon-bridged oligomers, are often multistep and typically yield only dimers. Herein, we report a facile one-pot synthesis of β-β methylene?bridged BODIPY oligomers. Installation of methyl groups at the α and γ-positions blocks competing sites and increases the core electron density, facilitating an electrophilic substitution with protonated paraformaldehyde. The methylene bridge and steric demand of the α-methyl groups enforce a large transition dipole moment angle, resulting in pronounced absorption-band splitting with a major feature of J-type exciton coupling. This mechanism is systematically elucidated using spectroscopy, single-crystal X-ray analysis, and TD-DFT (time-dependent density functional theory) calculations. The well-defined methylene-bridged oligomers established herein provide an ideal model system for studying exciton coupling and advance the design of functional dye architectures.