Covalent porphyrin-ruthenium(II) polypyridine dyads: From structure to photochemical properties and applications

Covalent porphyrin-ruthenium(II) polypyridine dyads represent a versatile class of molecular systems capable of using light energy to drive chemical reactions. Each component of their structure (the porphyrin unit, the covalent linker, and the ruthenium(II) polypyridine complex) plays a critical role in determining the overall performance of the dyad. The choice of the covalent linker, whether rigid (acetylene, phenyl), semi-rigid (amide), or flexible (carbon chains), strongly influences the efficiency and directionality of photoinduced processes, including energy and electron transfers, singlet oxygen generation, and excited-state population. Metalation of the porphyrin unit (Zn, Mn, Fe, Ni) further modulates the photophysical and redox properties, enabling applications of these dyads in photodynamic therapy (PDT), nonlinear optical devices, dye-sensitized solar cells (DSSCs), and dye-sensitized photoelectrosynthetic cells (DSPECs). This review provides an overview of covalent porphyrin-ruthenium(II) polypyridine dyads, summarizing reported structures, photophysical behaviors, and electron/energy transfer mechanisms, while highlighting the role of each structural component and exploring potential biological and technological applications of these systems.