Fabrication And Characterization Of Soft Luminescent Materials From Lanthanide Polyoxometalates And Polycations

Owing to the remarkable optical properties,molecularly defined lanthanide polyoxometalates(Ln-POMs)have been widely used in the preparation of functional materials as an ideal luminescent building block.However,the application of Eu-POMs in luminescent field is restricted due to the poor processability in solid state and the intensive quenching effect by solvent molecules,especially in aqueous solution.Co-assembling Eu-POMs into an ordered molecular aggregate matrix driven by various non-covalent interactions,can obtain soft materials with effectively improved processability and photophysical properties.In this dissertation,Eu-POM was used as a luminescent building block to co-assemble with polycations for constructing luminescent soft materials based on ion self-assembly.This strategy could achieve significant improvement in the luminescence performance of rare earth ions.Moreover,the sensitivity of building blocks to the external environment could be used to prepare stimulus-responsive rare earth luminescent materials.This dissertation includes the following two parts1.Branched polyethyleneimine(PEI),which can be protonated in water to carry positive charges,was used here to construct a luminescence enhanced nano-spherical soft material with an Eu-containing polyoxometalate(EuW10)in water through the ionic self-assembly(ISA)strategy.The protonated amine groups could effectively shield water molecules around EuW10 and result in significantly enhanced luminescence intensity,longer luminescence lifetime and higher quantum efficiency compared with EuW10 aqueous solution.Meanwhile,the sensitive coordination structure of EuW10 to environment made it possible to obtain materials used to detect copper ions.Moreover,based on the tunability of the protonation degree of PEI,the morphology and luminescence intensity of the aggregates were also pH-responsive This research represented a new designing strategy for constructing luminescence materials with responsiveness,and exhibited application potentials of them in detection by luminescence analysis2.A long-chain alkyl imidazole surfactant,C18mimBr(OB),was used to prepare a surfactant-encapsulated Eu-containing POM complex(SEP)through the electrostatic interaction.SEP could self-assemble in a polymerizable imidazole ionic liquid driven by solvophobic interaction and hydrogen bonding to obtain soft aggregate materials with a certain viscoelasticity.The aggregates were composed of micro-ribbons with layer structure.Then,in situ photopolymerization produced a red light-emitting polymer film with the ordered layer structure maintained.Due to the effective binding of C18mimBr to EuW10,the non-radiative transition deactivation was greatly reduced.Meanwhile,the photophysical properties exhibited by this soft material were better than those for others containing EuW10,which were also resulted from the isolation of EuW10 from each other and the confined microenvironment in molecular aggregates.It is worth noting that the ionic liquids as a solvent not only avoids the luminescence quenching effect compared with conventional solvent such as water,but also improves the stability and then increases the application range of this type of luminescent material.