Design,synthesis And Properties Of High Efficient Acetenyl Copper Photocatalysts

Photocatalysis has attracted considerable research interest because of its broad prospects in the fields of energy,environment and organic synthesis.To promote the practical application of photocatalytic technology and to reveal and deepen the understanding of the complex photocatalytic process and mechanism,the rational design and development of new and efficient photocatalysts has become one of the inevitable choices at this stage.In general,photocatalyst activity is mainly determined by the product of light absorption efficiency,carrier separation/transfer efficiency and interfacial reaction efficiency.Therefore,the development of photocatalytic system must consider the coordination optimization and tunability of the above three factors simultaneously to achieve a significant improvement of photocatalytic efficiency.Copper-phenylacetylide,an important active intermediate in copper catalyzed Sonogashira,Glaser and alkyny-azide cycloaddition reactions,not only has tunable organic alkyne monomers and one-dimensional Cu（I）-Cu（I）ladder charge transfer channel,but also has become one of the new photocatalysts with great development potential due to the inherent polarization of metal-alkynyl ligands and a variety of charge transfer pathways.However,the band gap of the traditional copper-phenylacetylide photocatalyst is about 2.34 e V,the absorption band edge is only 530 nm correspondingly,and it has obvious aggregation induced emission（AIE）characteristics due to the free rotation of the peripheral phenylacetylene group,resulting in low photocarrier separation efficiency and poor stability,which seriously hindrance the development and practical application of copper-phenylacetylide photocatalyst.To overcome the above defects of copper-phenylacetylide photocatalyst,explore and develop new and efficient alkynyl copper photocatalyst,and deepen the understanding of complex photoexcitation and charge transfer pathways of alkynyl copper,we constructed a series of new and efficient alkynyl copper photocatalyst by selecting different organic alkynyl monomers and Cu²⁺self-assembly.The structure-activity relationship,photogenerated charge transfer and photocatalytic mechanism were systematically studied,the specific work is as follows:1.A series of alkynyl copper photocatalysts（PACu,NACu,FACu and BACu）with orderedπstacking mode were prepared by solvothermal reaction of organic acetylene monomers（2-ethynylnaphthalene（NA）,9-ethynylphenanthrene（FA）,1-ethynylpyrene（BA））with different conjugated aromatic rings instead of phenylacetylene（PA）with Cu²⁺.The effect of conjugation regulation on the photocatalytic activity and stability of alkynyl copper was systematically studied.The results showed that with the increase of conjugation,the absorption spectrum of alkynyl copper photocatalyst was redshifted obviously,and the number of photocarriers,carrier separation and stability were increased significantly.In the performance evaluation,BACu showed that the conversion and selectivity were over 99%in air atmosphere of photocatalytic benzylamine oxidation and Glaser coupling reaction within 2 h and 3 h respectively.This work provides important reference for revealing the effect of aromatic ring conjugation on alkynyl copper photocatalyst,and also brings new enlightenment for the design of new efficient alkynyl copper catalyst.2.Utilizing a multi-channel charge separation strategy,the multi-alkynyl monomer was selected to replace the monomer in phenylacetylide copper（CP-1）and self-assembled with Cu²⁺,alkynyl copper photocatalysts CP-2P（copper p-diethynylbenzene）,CP-2M（copper m-diethylnylbenzene）and CP-3（copper 1,3,5-triethynylbenzene）with three-dimensional（3D）metal-organic polymer network structure were prepared.A large number of experiments combined with density functional thoery（DFT）theoretical calculation showed that CP-2P had the best photocatalytic activity.The 3D metal-organic polymer framework formed by copper-bridged p-diethynylbenzene monomer on the one hand greatly inhibited radiation recombination via multi-channel charge transfer to optimization photocatalytic activity;on the other hand,effectively stabilized monomers by multidirectional coordination,thus endowing CP-2P with ultra-high,universal photocatalytic activity and stability in photocatalytic thioanisole,benzyl alcohol and benzylamine oxidation.Meanwhile,CP-2P can be applied to large-scale photocatalytic organic synthesis driven by solar energy.In this system,¹O₂ is the main photocatalytic active species,which is generated by the spontaneous adsorption and activation of O₂ on the surface of CP-2P.This work demonstrates the feasibility of transforming alkynyl copper from excellent AIE material to high efficiency photocatalyst based on multi-channel charge separation strategy,and provides a novel idea for the development of high efficiency photocatalyst.3.The highly efficient alkynyl copper photocatalyst T₄EPE-Cu with photo-regulated reactive oxygen species generation was constructed by self-assembly of tetrakis（4-ethynylphenyl）ethene and Cu²⁺utilizing the various oxygen activation mechanisms of AIE aggregates and alkynyl copper units.In this system,transient photovoltage combined with DFT theoretical calculation revealed that alkynyl copper was the main site of oxygen adsorption and activation.Under high-energy photoexcitation,the adsorbed O₂ tended to produce·O₂^-because of the potential well effect of alkynyl copper unit.However,under low-energy photoexcitation,adsorbed O₂ tends to produce ¹O₂ via resonance energy transfer with alkynyl copper unit.Thus,the ratio of ¹O₂ products to·O₂^-products in the photocatalytic oxidation ofα-terpinene can be regulated from 1.3（380 nm photoexcitation）to 10.7（600 nm photoexcitation）.In addition,T₄EPE-Cu also showed ultrahigh photocatalytic performance for the Glaser coupling and benzylamine oxidation reaction with both a conversion and selectivity over 99%.This work provides interesting experimental results for the regulation of reactive oxygen species in photocatalysis,and points out the direction for the design of highly efficient and selective photocatalysts.