Preparation Of Carbazole Type Photosensitizers And Acylation Enabled By NHC/Photoredox Dual Catalysis

The carbazole-based organic photosensitizer designed and synthesized basing on carbazole can be used as a TADF material to dope organic materials due to its unique donor-πbridge-acceptor(D-π-A)structure.In electroluminescent devices,it also serves as a highly efficient photocatalyst to promote a series of challenging reactions.The currently reported carbazole-based organic optoelectronic functional materials have certain limitations in the application of organic synthetic chemistry.Therefore,it is has great scientific significance and practical value to design and synthesize highly efficient photosensitive dyes and broaden their application in organic synthetic chemistry.First,using 2,4,5,6-tetrakis(9-carbazolyl)-isophthalonitrile(4Cz IPN)as a general design template,by changing the number and position of carbazole groups and cyano groups on the central benzene ring and further changing the structure of the obtained D-A fluorescent molecules,we designed and synthesized 10 kinds of D-π-A type carbazole-cyano molecules with different electronic effects.Meanwhile,it’s structure was confirmed by NMR and high-resolution mass spectrometry.And the photophysical properties of organic molecules were studied by different changes in the positions and numbers of acceptors and donors of small organic molecules of photosensitizers by means of ultraviolet-visible absorption spectra and fluorescence emission spectra.With the rapidly development of NHC-catalyzed free radical chemistry,the synergistic catalysis of NHC-photoredox has shown better performance than that of a single catalytic system..Based on previous reports on free radical reactions catalyzed by nitrogen-heterocyclic carbene and light synergy,we realized that the skeleton structure of nitrogen-heterocyclic carbene has an important impact on the experimental results and catalysts containing thiazole and triazole skeletons are more advantageous.Therefore,by replacing amine compounds with different substituents,we designed and synthesized 12nitrogen heterocyclic carbene catalysts,including five thiazole-type carbene and seven triazole-type carbene.Subsequently,basing on the previous work,we successfully realized the direct C(sp~3)-H acylation reaction of methyl in DMAP by using NHC and photoredox synergistic catalysis.N-alkyl free radicals generated by alkylamines are coupled to obtainα-amino ketones efficiently and greenly.