Synthesis Of Novel Earth-abundant Zinc Complex Photosensitizers And Their Application In Carbon Dioxide Photoreduction

Fossil fuels generate high concentrations of greenhouse gases during the production capacity process,especially when the concentration of CO₂ in the atmosphere is too high,which will create serious environmental pressures.Therefore,the development of an efficient catalytic system using clean solar energy to drive CO₂reduction into fuel molecules is a challenging and important application issue.Homogeneous molecular catalytic systems include photosensitizers,catalysts and electron donors.Among them,photosensitizers play a vital role in photocatalysis as a light-absorbing center and an electron transfer bridge.However,the current use of photosensitizers is limited to precious metal complexes for instance[Ru（bpy）₃]²⁺.These complexes have limitations such as dependence on precious metals and weak absorption capacity of visible light,this severely limits the development of efficient and sustainable CO₂ photocatalytic systems.In order to solve the above problems,this paper designs and synthesizes efficient,inexpensive and stable zinc metal complex photosensitizers for photocatalytic CO₂ reduction,and build a cheap and sustainable photocatalytic system.In this paper,six zinc-metal complex photosensitizers（Z-1）were designed and synthesized by introducing anthracene-based units to the parent zinc complex（Z-1）,and by controlling the structure of dimethylpyrrole units and anthracene-based units,and by controlling the torsional steric resistance.Among them,Z-2,Z-4 and Z-6 are target complexes,and the solubility of the photosensitizer in the aqueous system is adjusted by introducing and controlling the number of ether chains.The 1,9-bit dimethyl of Z-3 and Z-5 is removed and the torsional resistance decreases.Z-1 does not carry an anthracene group as a control complex.The absorption spectrum researches displayed that these compounds all demonstrate a strongest absorbent band(ε>120000 M^-1cm^-1)at about 490 nm,indicating that they can efficiently capture visible light.Emission spectroscopy subjects have shown that the presentation of anthracene-based units can produce a charge transfer emission peak at 563 nm,and this zinc complex can perform efficient symmetrically broken charge transfer.Systematic studies have shown that Z-2,Z-4 and Z-6 with rigid structures have better excited state properties than other complexes,which is contributive to the efficient conversion of solar energy.The new zinc complex is further coupled with an iron catalyst（C-1）and a non-precious metal catalytic system is constructed for photocatalytic CO₂ reduction.Under visible light excitation,the catalytic system containing Z-6 exhibits the best catalytic performance,which can reduce CO₂ to CO with height efficiency and height selectivity,of which the CO yield reaches 110.5μmol,the TON is as high as 11056,and the quantum yield can reach 29.7%,which is importantly higher-up than the traditional precious metal photosensitizers[Ru（bpy）₃]²⁺and[Ir（ppy）₂（bpy）]⁺.Experimental and theoretical subjects have clarified the structure-property-activity relationship of photosensitizers,and proved that intramolecular charge transfer promotes intermolecular electron transfer,which in turn helps to achieve efficient photocatalysis.This paper improves the photocatalytic CO₂ reduction performance by developing efficient non-precious metal photosensitizers,which provides an important reference for the construction of sustainable and efficient photocatalytic systems.