Photo-triggered NO release of nitrosyl complexes bearing first-row transition metals and therapeutic applications

In biological systems, nitric oxide (NO) is a crucial signaling molecule that regulates a wide range of physiological and pathological processes. Given the significance of NO, there has been considerable interest in delivering NO exogenously, particularly through light as a non-invasive therapeutic approach. However, due to the high reactivity and instability of NO under physiological conditions, directly delivering NO to targeted sites remains challenging. In recent decades, photo-responsive transition metal–nitrosyl complexes, especially based on first-row transition metals such as Mn, Fe, and Co, have emerged as efficient NO donors, offering higher delivery efficiency and quantum yields than heavy metal–nitrosyl complexes under light exposure. This review provides a comprehensive overview of current knowledge and recent developments in the field of photolabile first-row transition metal–nitrosyl complexes, focusing on the structural and electronic properties, photoreactivity, photodissociation mechanisms, and potential therapeutic applications. By consolidating the key features of photoactive nitrosyl complexes, the review offers deeper insights and highlights the potential of first-row transition metal–nitrosyl complexes as versatile tools for photo-triggered NO delivery.