Construction Of Molecular Assemblies Based On Host-guest Interaction And Its Application In Light-haversting Systems

Photosynthesis is an important life activity for plants and animals in nature.It can efficiently convert light energy into chemical energy.The study of photosynthesis plays a guiding role in promoting agricultural production and environmental protection.The light-harvesting system is an important part of the photosynthesis system,which is composed of a large number of antenna molecules through ordered assembly.Photosynthesis begins from the absorption of photons by dye molecules in the light-harvesting system.These dye molecules,as energy donors,transmit the excitation energy to the energy receptor in the reaction center efficiently through energy transfer to induce a series of redox reactions.Therefore,it is of great significance to develop a highly efficient artificial light-harvesting system.In order to further explore the construction of artificial light-harvesting system,three new molecular assemblies are constructed through host-guest interaction based on the idea of supramolecular assembly,and a series of artificial light-harvesting systems with high energy transfer efficiency are obtained.The specific results are as follows:1.A double-headed amphiphilic salicylaldehyde azine derivative(BSA)was designed and synthesized,which showed weak light emission in aqueous solution and self-assembled to form a spherical aggregate structure with a size of ? 30 nm.After the addition of ?-cyclodextrin(?-CD),it can form a pseudorotaxane structure through the host-guest interaction.The encapsulation of ?-CD limits the free rotation of the N-N bond and excited-state intramolecular proton transfer(ESIPT)via intramolecular hydrogen bonds,BSA-?-CD exhibits aggregation-induced emission in aqueous solution,and the luminescence is significantly enhanced.At the same time,it can be assembled to form a spherical aggregate structure with a size of ? 20 nm in aqueous solution.Using the two molecular assembly systems described above as energy donors and sulforhodamine(SR101)as energy acceptors,two types of aqueous light-harvesting systems were constructed.Under the ratio of donor and acceptor at 166: 1,the energy transfer efficiency of the two light-harvesting systems is 18.2% and 41.7%,and the antenna effects are 9.8 and 84.5.The addition of ?-CD can significantly improve the energy transfer efficiency in light-harvesting system.2.An anthracene-alkyl pyridinium-type amphiphilic compound(AP)was designed and synthesized,which can form spherical nanoparticles in aqueous solution.The pyridinium moiety or the pyridinium and anthracene moieties in the AP structure can enter into the cavity of cucurbit[7]uril(CB [7])and cucurbit[8]uril(CB [8])through host-guest interaction respectively,which can self-assembly to form spherical aggregates and nanotube structures in aqueous solution.The Zeta potential test showed that the molecular assemblies of AP,AP@CB [7] and AP@CB [8] were all positively charged with potentials of +27,+67,and +18 m V,respectively.Using three positively charged molecular assemblies AP,AP@CB [7] and AP@CB [8] as energy donors,a negatively charged fluorescent dye Eosin(EY)as energy receptors,three aqueous light-harvesting systems have been constructed.When the ratio of donor to acceptor is 100: 1,the energy transfer efficiency and antenna effect of the three systems are 17.8% and 10.3,19.2% and 17.6,and 22.3% and 15.1,respectively.The light-harvesting system constructed by using three molecular assemblies with different assembly morphologies and the electrostatic force between the energy and the receptor reflects a certain difference in energy transfer efficiency.This provides an idea to further explore the light-harvesting system based on supramolecular assemblies.3.Using the "Click" reaction,an amphiphilic hydroxyflavone derivative(HFD)with a hydrophilic side chain modification was designed and synthesized.HFD is very soluble in water and shows a significant single fluorescent emission attributed to its anionic form.We found that cyclodextrin(CDs)can interact with HFD through host-guest interaction,the fluorenscent intensity of HFD can be controlled by CDs with different cavity sizes.The cavity of ?-CD is small,it is difficult to encapsulate HFD molecules,and it has no effect on the fluorescence.In contrast,with the increase of the cavity,?-CD and ?-CD can form 1: 1 and 1: 2 complexes with HFD,respectively,and the fluorescence intensity also increases and decreases,respectively.The main reason of fluorescence enhancement with ?-CD is that the self-quenching caused by the aggregation of HFD molecules is reduced after the host-guest encapsulation,and the decrease of fluorescence with ?-CD can be attributed to the enhanced ?-? stacking after encapsulating two HFD in a ?-CD.In addition,we also studied the self-assembly properties of HFD before and after addition of CDs.HFD and HFD-?-CD can self-assemble to form ? 100 nm spherical aggregates in aqueous solution,HFD-?-CD can self-assembles to form crosslinked nanoparticles,and HFD-?-CD can self-assembles to form ? 200 nm spherical aggregates,respectively.Using the above four molecular assembly systems as energy donors and the dye molecule Cy5 as energy acceptors,four light-harvesting systems have been constructed.When the ratio of donor and acceptor at 58: 1,the energy transfer efficiency and antenna effect of the four systems are 34% and 14.6,35% and 15.1,54.5% and 16.6,36% and 12.8,respectively.