Construction And Photocatalytic Oxidation Property Of The Photofunctional Mofs With 4,4’,4’’-triphenyltriene Carboxylic Acid

Photofunctional MOFs in photocatalytic oxidation reaction have become a research spotlight in green chemistry owing to its clean,recyclable and mild reaction conditions on the one hand;On the other hand,light absorption and excited-state redox potential can be efficiently regulated through the structural modulation of MOFs.In photocatalytic oxidation reactions,rapid electron transfer to form reactive oxygen species is the key to the reaction,however,the low visible light utilization,poor electrical conductivity and energy band position mismatch of MOFs limit the development of photocatalytic oxidation.The aim of this paper was to improve the conjugation of ligands by the introduction of vinyl double bonds,which promoted the absorption of visible light and the electron transfer rate.Two Zn-MOFs with excellent photocatalytic performance were constructed with Zn ions and rigid auxiliary ligands for efficient photocatalytic oxidation reactions by selecting vinyl double bond-modified 4,4’,4’’-triphenyltriene carboxylic acid（H₃TACPA）as a ligand.The main research contents and results were summarized as follows:（1）A three-dimensional metal-organic framework Zn-TACPA was constructed by photoactive H₃TACPA ligands,rigid conjugated auxiliary ligands 4,4’-vinylenedipyridine and zinc ions.Structural analysis showed that the threefold interpenetrated Zn-TACPA had1.4×1.1 nm² elliptical pore channels with dense distribution of unsaturated zinc sites and triphenylamine photo-oxidation sites in the pores.The unsaturated zinc sites in Zn-TACPA acted as Lewis acid catalytic coupled photooxidation and efficiently catalyzed the photooxidative cross-dehydrogenation coupling（CDC）/aromatization tandem reaction of glycine esters and styrene with 91%reaction yield.The results showed that the introduction of the double bond provided stronger light absorption and accelerated the electron transfer rate through conjugatedπ-πinteractions with the backbone,enabling efficient dual-path oxygen activation.And the reaction mechanism was further demonstrated by theoretical calculations,electron paramagnetic resonance and mass spectrometry.（2）Based on the excellent photoactivity of H₃TACPA ligand,a three-dimensional metal-organic framework Zn-TAAZ was constructed with 4,4’-azodipyridine and zinc ions.Structural analysis showed that Zn-TAAZ had a suitable rectangular pore channel of 1.33×1.35 nm² and its domain-limited pore structure matched quinuclidine.Photoredox site coupled HAT co-catalyst quinuclidine in Zn-TAAZ can catalyze the coupling reaction of benzyl alcohol and diethylamine with high efficiency and 93%reaction yield.It was shown that the suitable pore structure and excited-state redox potential of Zn-TAAZ facilitated the efficient electron transfer and achieved the multi-component synergistic catalysis of photo-oxidation,hydrogen atom transfer（HAT）and reactive oxygen species.Repeatability and stability experiments showed that Zn-TAAZ had high stability and recyclability.