Recent Advances on the Development of Early Transition Metal Complexes for Photo‐Assisted Cytotoxicity Applications

Abstract For targeted therapy, the strategic use of an inactive precursor or “prodrug” could be an attractive strategy. Photo‐assisted chemotherapy offers a smart opportunity for developing new inorganic prodrugs for selective and temporal regulation on the chemotherapeutic activity of the prodrugs with light. The 3d transition metal complexes with versatile coordination number and geometry, redox, thermodynamic and kinetic properties, the presence of low‐energy metal‐centered electronic transitions, and the ability to exhibit light‐assisted chemical reactions have emerged as strategic tools for photo‐chemotherapeutic applications. Transition metal complexes are typically characterized by metal‐centered, ligand to metal, metal to ligand or intra‐ligand electronic transitions, and photo‐activated electronic states of the transition metal complexes potentially exhibit a wide range of chemical reactions viz. intramolecular oxido‐reduction reactions, intramolecular rearrangements, ligand exchange reactions or energy transfer those cascades into the generation of ROS (⋅OH, O 2 − ⋅, O 2 2− , 1 O 2 ), small molecules like H 2 , N 2 , CO or NO, and alkyl or aryl radicals. Applications of photo‐activable transition metal complexes for generating cytotoxic ions or radicals in the presence of light have emerged as an attractive strategy for photo‐activated chemotherapy (PACT). Here in, we reviewed the photophysical and photochemical aspects of the early transition metal complexes exhibiting photo‐ activated chemotherapy.