Construction Of AIE Supramolecular Polymers And Their Application For Fabricating Light-harvesting Systems

Fluorescent supramolecular polymers(FSP)are important dynamic luminescent materials.The emergence of aggregation-induced emission(AIE)materials has laid the foundation for the application of FSP in practice.In this paper,a series of novel AIE-type FSPs based on different non-covalent interactions were constructed.The self-assembly behaviors of these FSPs were studied and their application in the field of light-harvesting systems was explored.This paper is mainly divided into the following four parts:In the first part,an FSP based on the host-guest interaction was developed.A benzo-21-crown-7(B21C7)functionalized by cyanostyrene derivative host molecule(H)with AIE properties was designed and synthesized.B21C7 could complex with the electron-deficient ditopic dialkylammonium salt guest molecule(G)and finally a novel FSP with blue fluorescence emission could be constructed.This FSP has potential application in the field of supramolecular luminescent materials.In the second part,an artificial light-harvesting system(LHS)based on quadruple hydrogen-bonded supramolecular polymer was developed.A ureidopyrimidinone(UPy)functionalized by tetraphenylethylene derivative(M2)with both supramolecular polymerization ability and AIE behavior was designed and synthesized.Water-soluble supramolecular polymer nanoparticles were formed by self-assembly of M2 under the mini-emulsion by the surfactant cetyltrimethylammonium bromide(CTAB).Using M2 as the energy donor and the hydrophobic fluorescent dye Nile Red(NiR)as the energy acceptor,an artificial LHS with high energy transfer efficiency and antenna effect was successfully constructed in an aqueous solution.Changing the ratio of the donor and acceptor could achieve tunable fluorescence emission from blue to pink,including white light.This highly effective water-soluble artificial LHS provides a reliable platform for mimicking photosynthesis.In the third part,a supramolecular artificial light-harvesting system with two-step sequential energy transfer was developed.Under the mini-emulsion of CTAB,M2 was self-assembled to form water-soluble supramolecular polymeric nanoparticles.4,7-di(2-thienyl)-benzo [2,1,3] thiadiazole(DBT)and2,6-disubstituted naphthalene diimide(NDI)were used as the relay acceptor and the final acceptor,respectively,to realize the secondary continuous energy transfer process.As a result,the excitation energy of M2 could be transferred into the final acceptor NDI through the relay acceptor DBT.The system not only exhibited tunable multi-color fluorescence emission from blue to yellow to red including white light,but also had a very high total antenna effect.The construction of multi-step energy transfer system provides a new perspective for in-depth mimicking the photosynthesis in nature.In the fourth part,a supramolecular artificial light-harvesting system based on a quadruple hydrogen bonded copolymer was developed.A bridged tetraphenylethylene-functionalized UPy derivative M3 with both supramolecular polymerization ability and AIE behavior was designed and synthesized.2,6-disubstituted naphthalimide-functionalized UPy derivative M4 could be copolymerized with M3 by quadruple hydrogen bonds.With the help of CTAB for microemulsion,the supramolecular copolymer could form nanoparticles in water.In the nanoparticles,M3 acted as energy donor and M4 played the role of an energy acceptor,resulting in the formation of an artificial light-harvesting system.By taking advantage of the flexibility of supramolecular self-assembly,the modulation of fluorescence emission from yellow to red could be achieved by changing the ratio of the donor to the acceptor.The energy transfer between M3 and M4 not only improved the fluorescence quantum yield of the system,but also reduced the half-peak width and increased the peak height,thus obtaining a relatively "pure" light source.