Visible Light-induced Carbon-hydrogen Functionalization Catalyzed By Organic Polymers

The use of solar energy to develop green and efficient synthetic methods is the key development direction of organic synthesis.Homogeneous photocatalysts have excellent catalytic activity and high selectivity,however,the inherent drawbacks of high price,poor stability,difficult separation from the reaction system,and low recyclability have prompted the construction of inexpensive and highly active heterogeneous catalysts.Porous organic polymers(POPs),with their structural designability,adjustable band gap,high specific surface area,good stability,uniform pore size,easy synthesis,and recyclability,have recently emerged as a powerful platform of heterogeneous photocatalysis and triggered a research boom.Porous organic polymers constructed with small-molecule organic photosensitizers(Eosin Y,Rose Bengal,BODIPY,4CzIPN,phenothiazine,and metal complexes)as their optical cores not only maintain the original catalytic activity,but also endow them with the cycling potential of heterogeneous catalysis.Meanwhile,the increased molecular rigidity after polymerization can effectively avoid photobleaching and increase the stability of photosensitizers.It also endows them with the properties of POPs in optical bandgaps,energy levels and inherent photoelectric performance,such as lightabsorption range,photogenerated charge lifetime,and transient photocurrent responses,which can be conveniently modulated,offering boundless possibilities for the design of new efficient heterogeneous photosensitizers and continuous optimization of their structure to meet the requirements of photocatalysis.In this dissertation,the diversity-oriented construction of 4CzIPN-based conjugated polymetric photocatalysts(CPPs)is successfully established,and the flexible regulation of structure is realized by simply altering the building blocks.The synthesized CPPs can be employed as heterogeneous photocatalysts for visible-lightdriven multi-functionalization of C(sp3)-H bonds to synthesize 87 final products with yields up to 99%.Time-dependent density functional theory(TD-DFT)calculations demonstrate that the photocatalysis performance of CPP3 is superior to the corresponding monomer 4CzIPN due to the enhanced intersystem crossing(ISC)process.Spin-orbit coupling calculations prove that the rate constant of ISC outcompetes that of reverse intersystem crossing(RISC).The rapidly generated and long-lived triplet state T1 is considered to be a more accessible excited state than the singlet state S1 generated from either direct excitation or RISC.Furthermore,the heterogeneous photocatalyst CPP3 is easily recovered from the reaction with excellent retention of photocatalytic activity,which can be reused at least for five times The successful application of this polymerization-enhanced photocatalysis strategy should guide a metal-free approach to the rational design of CPP-type heterogeneous photocatalysts to address the dilemma of homogeneous photocatalysts in sustainability,stability,and recyclability.