Carbon–carbon bonded BODIPY dimers: Structural classification, photophysical mechanisms, and functional applications

Covalently bonded BODIPY dimers have emerged as a versatile class of multichromophoric systems that exhibit rich structural diversity and highly tunable photophysical and photochemical properties. By coupling two BODIPY units through distinct linkage topologies, these dimers provide a unique platform for modulating electronic coupling, excited-state dynamics, and functional performance without relying on heavy atoms. This review presents a comprehensive and critical overview of single-bonded and π-fused BODIPY dimers, systematically classified according to their linkage modes, including α–α, α–β, α–γ, β–β, β–γ, meso-involving, γ–γ, and π-fused architectures. Beyond a structural taxonomy, we emphasize a unified structure–function paradigm, highlighting how linkage topology governs dihedral angle and interchromophoric electronic coupling, thereby dictating key excited-state pathways such as exciton splitting, intramolecular charge transfer (ICT), and spin–orbit charge-transfer intersystem crossing (SOCT-ISC). These mechanistic features directly translate into distinct performance advantages across applications, including photodynamic therapy, near-infrared fluorescence imaging, photoacoustic imaging, photocatalysis, and organic photovoltaics. Representative examples are discussed to illustrate how orthogonal single-bond dimers favor efficient triplet-state formation and reactive oxygen species generation, whereas π-fused dimers exhibit enhanced near-infrared absorption and non-radiative energy dissipation. By integrating molecular structure, photophysical mechanism, and application outcome, this review provides rational design guidelines for next-generation BODIPY dimers tailored to specific photonic and biomedical functions.