AIE-active Carbonyl Compounds,and Folded Small Molecules And Polymers:Synthesis,Properties And Applications

Developing efficient solid-state luminescent materials was a great challenge in the past years and a large number of studies had been carried out on it.It's worth mentioning that the aggregation-induced emission(AIE)phenomenon firstly reported in 2001 has made enormous contribution to this filed.So far,researchers have done extensive researches based on AIE materials.AIE materials emit weakly in solution but show strong luminescence in the aggregated state.It is not exaggerated to say that the discovery of AIE is a landmark in the development history of the luminescent materials.The most widely studied AIE materials are the derivatives of siloles and tetraphenylethene(TPE),and the applications of AIE materials have extended to organic light emitting diode(OLEDs),biological imaging,fluorescent probe,and so on.At the same time,many new AIE systems have been developed,including a series of folded TPE derivatives.Based on the mechanism of AIE,we had explored a new AIE system with carbonyl and synthesized folded TPE derivatives with aggregation-enhanced emission(AEE)properties.And then the folded structure was introduced into the polymers to build new AEE polymers.Subsequently,the applications of the folded fluorescent materials in OLEDs and explosive detection were evaluated.The specific works as follows:(1)It is well known that pyrene is a planar ? conjugated molecule,and it is inclined to cause fluorescence quenching due to the strong intermolecular ?-? interaction in the aggregated state,that is to say it's a typical ACQ material.However,we found that some pyrene derivatives exhibit AIE characteristics.To figure out the working mechanism,we designed and synthesized a series of new pyrene derivatives,and studied the effect of substituents on the luminescence behavior of the compounds.Then the structural features and optical properties of these compounds were studied,and theoretical calculation was conducted.We found that there were various interactions between molecules in the crystal packing structure,which was beneficial to the enhancement of solid state luminescence.Theoretical calculations showed that the geometric conformations of S1 and S0 in single molecular state greatly changed,which caused weak emission in solution,but S1 and S0 in solid were almost identical in the solid state.So the restriction of intramolecular motions(RIM)mechanism can explain the AIE phenomenon of these pyrene derivatives.(2)By Friedel Crafts reaction,Suzuki reaction and McMurry reaction,we use biphenyl,fluorene and pyrene,triphenylamine as raw materials to prepare a series of through-space conjugated luminescent materials f-DBP-DBPE,f-DBP-DFLE,DBP-DPy and DBP-DTPA.All products exhibited aggregation-enhanced emission(AEE)characteristics.Whereas f-DBP-DBPE and f-DBP-DFLE had folded configurations,DBP-DPy and DBP-DTPA were linked by a single bond due to the steric hindrance.Due to the presence of intramolecular through-space conjugation,free movement of some parts was blocked.Differing from the traditional AIE materials,their quantum yields had been enhanced to 50% in solution and could approach 100% in solid state.The multilayer non-doped OLED devices based on this folded material exhibited excellent performance,affording high luminance up to 49030 cd m-2 and the maximum external quantum efficiency of up to 2.5%.(3)In this part,we introduced a folded unit with through-space conjugation into the main chain to prepare a series of new AEE polymers.The absorption peak of these polymers were distributed in 328-612 nm.The polymers emitted green,yellow green or red fluorescence.The green and yellow green-emitting polymers exhibited high quantum yields(34%-46%)both in solution and solid states.We compared the detection sensitivity for trinitrophenol(PA)of the polymers in pure THF solution and THF/water mixed solution with 80% water content.The results once again verified the superamplification effect of nanoparticles in the aqueous media.The maximum quenching constant in the mixed solution is 5.52 × 105 M-1,which was much higher than that in pure THF solution of 7.82 ×104 M-1.