Efficient Aggregation-Induced Emission Based On Polymer Hosts Materials For Construction Of Artificial Light-Harvesting Systems

Luminescence is an exotic phenomenon,which have played important roles in various fields spanning from illumination,fluorescent signage and fluorescence analysis,etc.With the rapid development of modern materials science,the eye-catching achievement in the scope of photoluminescent materials has assisted us to attain deeper understanding from fundamental mechanisms to real-world applications.Traditional luminophores have suffered from the notorious aggregation-caused quenching(ACQ)effect due to unwanted?-?interactions,which severely limits their widespread applications in a number of research areas.As a ground-breaking solution,Tang and co-workers reported aggregation-induced emission(AIE)phenomenon,and developed a large array of luminogens with AIE feature,referred as AIEgens,which have proved to be effective in ion detection,bioimaging,photodynamic/photothermal therapy,artificial light-harvesting systems,etc.At present,it is still a challenging and cutting-edge research topic in terms of developing efficient AIE materials and implementing their applications.Therefore,this paper is devoted to exploring efficient AIE systems by marrying supramolecular chemistry and polymer chemistry with the aid of synergetic effects involving hydrophobic interactions and host-guest interactions endowed by polymer host materials.We designed and synthesized linear copolymer hosts bearing a number of pillar[5]arene units dangling side chains,referred as polymer hosts,which could be utilized to fabricated supramolecular polymer networks and supramolecular polymer nanoparticles with a series of tetraphenylethylene(TPE)-based tetratopic guests.We presented a strategy to construct AIE systems with high quantum yields with the concurrent aid of the confinement of macrocycles and the steric hindrance of bulky polymers,which was named as double confinement strategy.This paper can be summed up as the following three parts:(1)Firstly,we came up with our double confinement strategy in order to improve fluorescent quantum yields by using typical AIEgens—TPE derivatives as model compounds.We designed and synthesized vinyl-based monomers involving a pillar[5]arene unit(MMAP[5]A),and then prepared a class of amphiphilic copolymer hosts material with pillar[5]arene units dangling side chains,i.e.,poly(methyl methacrylate-co-methacrylamide-co-mono methacrylate pillar[5]arene),denoted as poly(MMA-co-MAAm-co-MMAP[5]A),by RAFT polymerization using methyl methacrylate(MMA),methacrylamide(MAAm)and MMAP[5]A as monomers.Supramolecular polymer networks with dramatically enhanced fluorescence intensity were fabricated by employing polymer hosts and TPE derivatives terminated by guest moieties including alkyl-cyano-group,triazole-alkyl-cyano-group and alkyl-bromine-group.Several parameters that impact fluorescence intensity of supramolecular polymer networks were investigated in detail,such as,the structures of polymer hosts,binding affinity of host-guest interactions,density of pillar[5]arene unit at side chains,and different solvent types.An efficient supramolecular polymer networks with quantum yields of 98.22%were attained by optimizing conditions,indicating the strategy works effectively.Finally,we investigated the assembly-disassembly of supramolecular polymer networks under the stimuli of temperature and competitive agents based on the reversible host-guest interactions.These researches should not only enrich the types of efficient supramolecular AIE systems,but also illustrated restriction of rotation(RIR)-ruled mechanism.(2)The supramolecular polymer networks fabricated by polymer host and TPE derivatives can further form luminescent supramolecular polymer nanoparticles by host-guest interactions and hydrophobic interactions.Generally speaking,it is a challenging task to construct photoluminescent supramolecular polymer nanoparticles in THF/H₂O mixture solution due to the ACQ effect of chromophores.We prepared supramolecular polymer nanoparticles by using poly(MMA-co-MAAm-co-MMAP[5]A)and TPE derivatives and then investigated their fluorescence enhancement in THF/H₂O mixed solvent.The fluorescence intensity of supramolecular polymer nanoparticles were increased with the increasing water fraction,indicating the AIE feature of such materials.Meanwhile,the hydrodynamic diameters(D_h)of nanoparticles were decreased to ca.200 nm upon addition of water in mixed solvent due to the hydrophobic effect of polymer hosts.We claimed that the the larger water fraction led to more condensed structure and resulted in enhanced fluorescent intensity due to RIR working mechanism.Furthermore,the density of pillar[5]arene unit that impact the fluorescence intensity was investigated in detail.The polymer host with loose pillar[5]arene unit could form larger supramolecular nanoparticles which was responsible for enhanced fluorescence performance.Finally,artificial light-harvesting systems based on spherical supramolecular nanoparticles are constructed by incorporating 9,10-distyrylanthracene(DSA)derivatives terminated with triazole-alkyl-cyano group into supramolecular nanoparticles.By adjusting the molar ratio of donor and acceptor,supramolecular polymer nanoparticles were constructed with tunable colors,from cold to warm tones.Instructed by double refinement strategy,we fabricated supramolecular polymer nanoparticles from supramolecular polymer networks by selecting solvent types.Such fluorescent nanoparticles show potential application in bioimaging and data storage.(3)It is worthwhile to fabricate single luminogen systems with enhanced fluorescence emission and adjustable emission wavelength in the scope of photoluminescent materials,however,the emission wavelength of almost all AIEgens could not be adjusted.We designed and synthesized a series of cyanovinylene-based(CV)derivatives functionalized with guest moieties,which exhibited bathochromic emission when compared with their isolated states due to the formation of dimers in aggregated states.Random copolymers bearing pillar[5]arene units dangling side chains were synthesized by RAFT polymerization,i.e.,poly(oligo(ethylene glycol)methyl ether methacrylate-co-methyl methacrylate-co-mono methacrylate pillar[5]arene),denoted as,poly(OEGMA₃₀₀-co-MMA-co-MMAP[5]A).Supramolecular polymer nanoparticles were prepared using poly(OEGMA₃₀₀-co-MMA-co-MMAP[5]A)and CV guest molecules with enhanced fluorescence intensity and tunable fluorescence wavelength due to the restriction of intramolecular motions and the prevented dimer formation for CV derivatives.These experimental results indicating that the packing modes of CV derivatives in solution could be regulated by polymer hosts bearing pillar[5]arene units to further improve optical properties.Artificial light-harvesting systems were well established by interweaving Nile Red and CV derivatives with polymer hosts with the emission colors changed from green to orange.In this section,we expand the scope of chromophores from TPE to CV,and further demonstrated that high efficiency and universality of AIEgens regulated by polymer hosts with the aid of double confinement strategy.