Photosensitizers based on Ir(III) complexes for highly efficient photocatalytic hydrogen generation

Abstract A series of new cationic Ir(III) complexes [Ir(C∧N) 2 (ppba)][PF 6 ] P1 – P5 as photosensitizers (PSs) has been rationally designed and synthesized. According to the study of photocatalytic hydrogen generation from water based on these five Ir(III) PSs, the highest yield of hydrogen generation has been achieved by P5 , in which the strong electron-withdrawing substituent, 2,6-difluoropyridine, is adopted to cyclometalated ligands. Moreover, the hydrogen generation yield of P5 is ca. 11 times than that of P3 , revealing that the hydrogen generation activity of PSs can be effectively improved through the variation of cyclometalated ligands. Based on the discussion of light absorption, charge separation and electron transfer processes, P3 with the broadest absorption and the highest molar absorption coefficient in the visible region displays the best visible light absorption capacity among P1–P5 due to the attribute of electron-donating substituent (benzothiazole). As the introduction of 2,6-difluoropyridine substituent, P5 with the longest excited-state lifetime and the greatest potential difference between E (TEA + /TEA) and E (PS ∗ /PS − ) among P1–P5 possesses the best charge separation and electron transfer capacities. These results illuminate that the introduction of electron-withdrawing substituents into cyclometalated ligands is beneficial for the improvement of hydrogen generation activity in this system. This article reveals that it is important to take into full consideration the relationship between structure and performance for the design of highly efficient PSs.