Substrates in excited state differ significantly from the corresponding ground state so that they are treated as different chemical species with diverse physical properties and chemical reactivity. Therefore, applying photocatalytic systems to activate substrates becomes increasingly popular. Although photosensitizers serve as the core of the photocatalytic reaction, the design of a photosensitizer has not been taken for granted. By modifying ligands of organometallic complexes to optimize properties of photosensitizers, we successfully achieved a series of iridium complexes with long excited triplet-state lifetime, high triplet excited-state energy, strong absorption, and robust stability. The efficacies of the prepared iridium complexes as photosensitizers were evaluated toward various challenging photocycloaddition reactions (e.g., thia-Paternò–Büchi reaction and multicomponent one-pot aza-photocyclization) between heterocyclic compound maleimides and unsaturated moieties that are not efficient to complete with well-established photosensitizers.

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