Development of Strong Visible-Light-Absorbing Cyclometalated Iridium(III) Complexes for Robust and Efficient Light-Driven Hydrogen Production.

Abstract

Weak light absorption of common Ir(III) complexes (e. g., using phenylpyridine as the ligand) has hindered their applications in photocatalytic hydrogen generation from water as an efficient photosensitizer. To address this issue, a series of cyclometalated Ir(III) complexes (Ir1-Ir5), featuring different electron-donating substituents to enhance the absorptivity, have been synthesized and studied as photosensitizers (PSs) for light-driven hydrogen production from water. Ir6-Ir7 were prepared as fundamental systems for comparisons. Electron donors, including 9-phenylcarbazole, triphenylamine, 4,4'-dimethoxytriphenylamine, 4,4'-di(N-hexylcarbazole)triphenylamine moieties were introduced on 6-(thiophen-2-yl)phenanthridine-based cyclometalating (C^N) ligands to explore the donor effect on the hydrogen evolution performance of these cationic Ir(III) complexes. Remarkably, Ir4 with 4,4'-dimethoxytriphenylamine achieved the highest turn-over number (TON) of 12 300 and initial turnover frequency (TOFi ) of 394 h-1 , with initial activity (activityi ) of 547 000 μmol g-1 h-1 and initial apparent quantum yield (AQYi ) of 9.59 %, under the illumination of blue light-emitting diodes (LEDs) for 105 hours, which demonstrated a stable three-component photocatalytic system with high efficiency. The TON (based on n(H2 )/n(PSr)) in this study is the highest value reported to date among the similar photocatalytic systems using Ir(III) complexes with Pt nanoparticles as catalyst. The great potential of using triphenylamine-based Ir(III) PSs in boosting photocatalytic performance has also been shown.