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

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.

Panchromatic Sensitization with ZnII Porphyrin-Based Photosensitizers for Light-Driven Hydrogen Production.

Three molecular photosensitizers (PSs) with carboxylic acid anchors for attachment to platinized titanium dioxide nanoparticles were studied for light-driven hydrogen production from a fully aqueous medium with ascorbic acid (AA) as the sacrificial electron donor. Two zinc(II) porphyrin (ZnP)-based PSs were used to examine the effect of panchromatic sensitization on the photocatalytic H2 generation. A dyad molecular design was used to construct a difluoro boron-dipyrromethene (bodipy)-conjugated ZnP PS (ZnP-dyad), whereas the other one featured an electron-donating diarylamino moiety (YD2-o-C8). To probe the use of the ZnP scaffold in this particular energy conversion process, an organic PS without the ZnP moiety (Bodipy-dye) was also synthesized for comparison. Ultrafast transient absorption spectroscopy was adopted to map out the energy transfer processes occurring in the dyad and to establish the bodipy-based antenna effect. In particular, the systems with YD2-o-C8 and ZnP-dyad achieved a remarkable initial activity for the production of H2 with an initial turnover frequency (TOFi ) higher than 300 h-1 under white light irradiation. The use of ZnP PSs in dye-sensitized photocatalysis for the H2 evolution reaction in this study indicated the importance of the panchromatic sensitization capability for the development of light absorbing PSs.

Starburst Triarylamine Donor-Based Metal-Free Photosensitizers for Photocatalytic Hydrogen Production from Water.

Three metal-free molecular photosensitizers (S1-S3) featuring a starburst triarylamine donor moiety have been synthesized. They show attractive photocatalytic performance in visible light-driven H2 production from water in their platinized TiO2 composites. A remarkable H2 turnover number (TON) of 10 200 (48 h) was achieved in an S1-anchored system.