Strongly emissive long-lived<sup>3</sup>IL excited state of coumarins in cyclometalated Ir(<scp>iii</scp>) complexes used as triplet photosensitizers and application in triplet–triplet annihilation upconversion
as triplet photosensitizers for triplet–triplet annihilation upconversion and upconversion quantum yields up to 22.8% were observed. Our results are useful for the preparation of visible light-harvesting transition metal complexes, the study of the tripletexcitedstate of organic chromophores, as well as the application of these visible light-harvesting transition metal complexes as efficient triplet