2,7-Bifluorenylidene-Linked Conjugated Porous Polymers: Molecular Design,Preparation And Photocatalysis

Organic conjugated porous polymers feature precisely designable molecular structures,tunable porous structures and surface areas,as well as rich electrical properties,showing potential applications in the fields of environmental protection,industrial catalysis,energy storage and conversion,etc.Among them,different from conjugated small molecules or polymers,conjugated porous polymers possess extended?-conjugated backbones,and enable exerting unique effects on some directions,such as photocatalytic mass transformation,which is relatively difficult to be realized by those traditional organic semiconductors.Regard to these,hereby,we started from the design and synthesis of new conjugated porous polymers,and exploring their photocatalytic activities toward dye degradation,and establishing the relationship between structures and properties.The main research contents are described as below:1.Design and preparation of 2,7-bifluorenylidene-linked conjugated porous polymers:A series of conjugated porous polymers based on the2,7-linked 9,9'-bifluorenylidene,were prepared by using2,2',7,7'-tetrabromo-9,9'-bifluorenylidene as the key monomer for a self-polymerization under transition metal-catalyzed Yamamoto polymerization,self-polymerization,or a copolymerization with2,2'-?9,9-Dimethyl-9H-fluorene-2,7-diyl?bis[4,4,5,5-tetramethyl-1,3,2-diox aborolane],1,4-benzenediboronicacid,2,2'-[1,1'-biphenyl]-4,4'-diylbis[4,4,5,5-tetramethyl-1,3,2-dioxaborolane]or 1,3,5-tris?4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl?benzene upon Suzuki-Miyaura cross-coupling reaction.Their chemical structures were characterized by ¹³C CP/MAS NMR and FT-IR spectra.Combination with TGA analysis,their high thermal stability can be observed.Meanwhile,their high polymerization degrees can be verified.2.Characterization of morphologies and physical properties of these target porous polymers:The morphologies of different polymers and the same polymer with different polymerization time were characterized by SEM and TEM.It can be found that the polymerization time had a certain influence on the morphologies of these target polymers,for example,from core-shell to tubular structures,which is high valuable for the evaluation of the possible mechanism of a certain morphology of porous polymer.At the same time,the obtained polymers were found to have typical amorphous states,hierarchical porous structures.Also,the solid UV-vis DRS and electrochemical CV tests indicated that the as-prepared polymers had strong light-harvesting abilities with the relatively narrow band gaps between 1.82 eV².27 eV.Their rich electronic structures and hierarchical porous structures could be purposefully tuned through the building blocks.3.Photocatalytic activities of the target porous polymers toward dye degradation:By using methylene blue?MB?,rhodamine B?RhB?and methyl orange?MO?as three different model pollutants for degradation,we found that the porous polymers could efficiently catalyze dye degradation under visible light or even natural sunlight with high reusability.Meanwhile,these porous polymers also exhibited highly selective degradation activities toward different dyes.These results are among the best value for the porous polymer-based photocatalysts.The photodegradation mechanism involving oxygen and electron,was also elucidated for the first time for such kind of materials,related to the presence of specific 9,9'-bifluorenylidene units in their?-conjugated skeletons.