Symmetry-breaking charge transfer in BODIPY-, porphyrin-, and phthalocyanine-derived symmetric dimers

Symmetry-breaking charge transfer (SB-CT) has become a fundamental excited-state process through which symmetric molecular assemblies create polarized charge-separated states without permanent donor-acceptor asymmetry. By leveraging electronic degeneracy, vibronic coupling, and environmental stabilization, symmetry-breaking charge separation (SB-CS) enables directional charge separation with minimal energy loss, offering a strong alternative to traditional donor-acceptor systems. In this review, we offer a thorough and comparative analysis of SB-CT across three main π-conjugated chromophore groups: BODIPYs, porphyrins, and phthalocyanines. We begin by establishing the foundational concepts of SB-CT and its connection to twisted intramolecular charge-transfer states, exciton-charge-transfer mixing, and mixed-valence systems. Key molecular structures within each dye family are then examined, highlighting how electronic coupling, molecular symmetry, solvent effects, and supramolecular organization influence charge-separation efficiency and recombination pathways. A unified framework is created to identify both universal SB-CT design principles and chromophore-specific behaviors. Lastly, we explore the implications of SB-CT for artificial photosynthesis, molecular photovoltaics, and photocatalysis, and outline key challenges and future directions for integrating SB-CT into catalytic and solid-state platforms. By linking fundamental photophysics with molecular design, this review positions symmetry-breaking charge transfer as a central guiding principle for next-generation molecular energy conversion systems.