This presentation highlights recent advances from our group in photochemical rearrangements involving diradical intermediates. Recently, we developed a di-π-ethane rearrangement of cyano groups via energy-transfer catalysis, enabling the efficient construction of strained three-membered ring scaffolds. Building on this, we extended this newly developed photochemical rearrangement to accommodate various functional groups, including aryl and pyridyl moieties, and successfully achieved their migration and cyclisation. More recently, we have applied this approach to photochemical ring-expansion reactions, offering a novel route from simple ring systems to complex medium-sized rings. Additionally, employing a radical–polar crossover strategy, we have also applied this method to the synthesis of heteroatom-containing bioisosteres.