Selective Synthesis And Luminescent Properties Of Polyene Ketone From α-active Pyrylium Salts

In recent years, organic conjugated polyene compounds have drawn much attention due to their unique electronic structures and photoelectric properties. However, synthesis of conjugated polyene usually requires a multistep or harsh reaction conditions. Meanwhile it is difficult to separate pure compound from products because of the isomerism of double bonds. In this thesis, a series of α-active pyrylium salts are syntheized by HClO4/O2oxidation of cyclopentadiene derivatives. Based on this, a strategy for stereoselective synthesis of (2E,4E,6E,8E)-decatetraene diketone by one-step metal reduction of α-active pyrylium salts is developped. As well the structures, thermal stabilities, optical and electrochemical properties of cyclopentadiene derivatives, α-active pyrylium salts and decatetraene diketone derivatives have been studied. The research contents are as follows:(1) Synthesis and properties of aryl-substituted cyclopentadiene derivatives. Cyclopentadiene derivatives are not noly the raw materials for α-active pyrylium salts, but also a kind of important small molecule-based electroluminescent material. In this section, Seven cyclopentadiene derivatives were synthesized and their structures were characterized by1H NMR,13C NMR, HRMS, MS and X-ray analysis. Their thermal stability, electrochemical and optical properties were investigated. And the results showed that cyclopentadiene derivatives display a typical aggregation-induced emission enhancement (AIEE) property. The relationship bewteen structures and properties was illustrated by X-ray analysis.(2) Synthesis and luminescent properties of aryl-substituted α-active pyrylium salts. Seven α-active pyrylium salts were synthesized by oxidation of cyclopentadiene derivatives with HClO4/O2. Their structures were characterized by1H NMR,13C NMR, HRMS, MS and X-ray analysis. The thermal stability, electrochemical and optical properties of these compounds were investigated. As a result, a tunable fluorescence was achieved by changing aryl groups on pyrylium ring, which indicated their potential application as light-emitting materials.(3) Selective synthesis and properties of decatetraene diketone compounds. Seven decatetraene diketone compounds were synthesized by metal reduction of α-active pyrylium salts and their structures were characterized by1H NMR,13C NMR, HRMS, MS and X-ray analysis. The optimal reaction conditions are as follows:with Mg as metal, CH3CN as solvent, reflux under Ar for4～6h. The relationship between reactivity and structure of pyrylium salts is discussed. As a result, reduction of α-active pyrylium salts afforded only linear (2Z,4Z,6Z,8Z)-decatetraene diketone derivatives, while reduction of α-non-active pyrylium salts generated compounds with diverse structures. TGA and DSC analysis showed these compounds possess a high thermal stability. The origin of weak fluorescence of these compounds was related to a twisted ’S’ configuration found in their crystalline structures.(4) Molecular modification and tunable luminescent properties of decatetraene diketone compounds. Main group elements such as N, S and Si were introduced into the backbone of decatetraene diketone compounds to improve their luminescent performance. Three new decatetraene diketone compounds with terminal groups of thiophene, triphenylamine and trimethylsilys phenyl were synthesized and their structures were characterized by1H NMR,13C NMR and HRMS. Fluorescent spectra and electrochemical tests that the introduction of eletron-donating groups incresed the fluoresent intensity and narrows the energy gap. Especially, the introduction of triphenylamine improved the fluoresent intensity by several hundred times.