Nature chemistry: Professor Turro's realization of water decomposition induced by single molecule chromophore catalyst under infrared light

1 Background, homogeneous emulsion or covalent or supramolecular systems usually consist of two parts photosensitizers and catalysts These catalytic systems can transform abundant raw materials into high energy chemicals Such as extracting hydrogen from water / formic acid or formic acid / methane system; extracting CO from CO 2 These processes require the use of pyridine ruthenium (II) complexes, ring iridium (II) complexes or porphyrins to achieve photon capture and charge transfer processes The homogeneous or heterogeneous catalyst can realize the single electron or multi electron reaction process matching the redox potential of its photosensitizer in the excited state Generally speaking, the photocatalysis process is to simulate the photosynthesis process Photoreaction I and photoreaction II use chlorophyll to absorb photons, and then electron hole separation Photon energy oxidizes water to get oxygen under the action of Mn catalyst Then electron shuttle is realized through electron transfer, and finally energy is stored in chemical bond The photocatalysis of multicomponent system has made great progress In particular, the use of cheap metal biomimetic catalyst can achieve tens of thousands of tons At the same time, it is difficult to realize the distributed light capture, catalytic center and / or electronic shuttle What's more, the heterogeneous system of polychromatic system needs the interaction of photosensitizer and catalyst in a specific distance and orientation Although great progress has been made, it is still difficult to control the surface and internal assembly of supramolecular Moreover, the above systems usually have poor light capture ability in the specific infrared or near infrared region, because the photooxidation process needs a large propulsion force to realize the multi electron conversion process Therefore, systems that can absorb infrared or near-infrared light usually have lower excited state energy levels and shorter lifetime Therefore, the time of molecules in high energy state is reduced 2、 Recently, the research team of Professor C Turro of Ohio State University has realized photolysis of water under infrared or near-infrared light by using single molecule chromophore photocatalyst The related research work was published in nature Chemistry (DOI: 10.1038 / s41557-019-0397-4) (photo source: Nat Chem.) 3 Compared with the multi-component catalysis system, the single molecule chromophore photocatalyst without discrete photosensitizer is rare For this reason, the author has synthesized bimetallic Ru single molecule chromophore photocatalyst for research It can be seen from the electronic absorption spectrum that the catalyst has an obvious absorption peak in the visible to near infrared region, and its maximum absorption peak appears at 624 nm It is found that the catalyst has a high ton value As shown in the figure below, irradiating catalyst 1 dissolved in DMF with red light (670 nm), adding charge donor 1-benzyl-1,4-dihydronicotinamide (BNAH) and p-toluenesulfonic acid (TsOH), it can be observed that in the first 3 hours, the value of ton is 84, and the highest value of TOF is 28 H-1; after irradiating for 24 hours, the maximum value of ton is 170 ± 5 In order to further understand the reaction mechanism of the catalyst, the author carried out in-depth study They first synthesized an electron reduced [1] 1-structure and tested its absorption spectrum; then added BNAH, the spectrum would not change; then used the red light of 670 nm to irradiate, found that the absorption spectrum changed, and generated [1] 2 -; when they continued to add TsOH into the reaction liquid, found that hydrogen was generated, and the intermediate [1] 2-changed to 1 This evidence fully shows that the intermediate [1] 2 - is the active center of the reaction (photo source: Nat Chem.) 4 Research conclusion professor Turro's research group has realized the photodegradation of water under the condition of infrared or near infrared light by using the single molecular chromophore photocatalyst, and explored the reaction mechanism, and finally found that the intermediate [1] 2 - is the active center of the reaction.