Synthesis,Structures And Properties Of Tellurium-Doped ?-Extended Aromatics

Tellurium is a unique element among chalcogens which often demonstrates metallic properties although it is classified as a non-metallic element.Tellurium is widely used in metallurgy,electronics,organic thin-film transistors,and solar cells.In recent years,tellurium-containing polycyclic aromatic hydrocarbons have received increasing attention as organic functional materials.However,the challenge in the preparation and the resultant lack of structural diversity is the main reason,if not the entire reason,that limits their wide applications.The synthesis of tellurium-containing polycyclic aromatic hydrocarbons often suffers from multistep synthesis,substrates that are not readily available,or low yields.Therefore,it is important to develop a simple and general method for the synthesis of tellurium-containing polycyclic aromatic hydrocarbons.In this dissertation,we have developed a convenient synthesis of tellurium-containing polycyclic aromatics from readily available cyclic diaryliodonium salts and tellurium powder under transition-metal-free conditions.This reaction can be applied to the synthesis of large?-extended ladder-type or bowl-shaped tellurium-containing materials thought multifold reactions.This method features mild conditions,high yields and excellent functional group tolerance.Furthermore,we revealed for the first time that some dibenzotellurophenes demonstrate fascinating room-temperature phosphorescence.This dissertation includes the following four parts:Part ?:We have a brief introduction on the research status of organic tellurium compounds,and the original design of my research.This section mainly focuses on some of the unique properties of tellurium-containing aromatic compounds such as the heavy atom effect,strong intermolecular interactions,and narrow band gaps.Part ?:The easy synthesis of cyclic diaryliodonium salts and good air/moisture stability make them ideal starting materials for the construction of various aromatic heterocycles.We thus decide to explore the synthesis of tellurium-containing aromatics from cyclic diaryliodonium salts.In this section,we prepared various cyclic diaryliodonium salts.First,various substituted2-aminobiphenyl compounds can be synthesized by Suzuki coupling reaction,and2-iodobiphenyls can be obtained through diazotization and Sandmeyer reaction,and then cyclic diaryliodonium salts were obtained from the 2-iodobiphenyls through oxidative cyclization.Thus prepared iodonium salts will be used as starting materials for the synthesis of tellurium-containing polycyclic aromatic hydrocarbons.Part ?:In this chapter,we mainly describe our efforts on the synthesis of tellurium-containing polycyclic aromatic compounds using cyclic diaryliodonium salts as starting materials.First,we have a brief overview of the reported synthesis of tellurium-containing aromatics.Then,after a wide screening of reaction conditions,the optimized reaction conditions were determined:diaryliodonium salts?1.0 eq?,tellurium powder?1.5 eq?,2-methylpyridine?1.0m L?,DMSO?2.0 m L?,N₂,120 ^oC.Various substituted dibenzotellurophenes as well as?-extended ladder-type and bowl-shaped tellurium-containing aromatics have been achieved by this newly developed method.Most of the synthesized compounds show good air/humidity stability and high thermal stability.This synthetic method has the following advantages:?1?The starting materials are stable and readily available;?2?Wide substrate scope;?3?Synthetically challenging tellurium-containing ladder-type semiconductor materials and bowl-shaped sumanene could also been achieved.Furthermore,we proposed a possible mechanism of this reaction based on some control experiments.Part ?:This part mainly studies the optical properties of prepared tellurium-doped polycyclic aromatic hydrocarbons.Pure organic room-temperature phosphorescent materials are of great interests and have received continuing attentions,but at present,the types of such materials are still very limited.Through spectroscopic studies,we found for the first time that some dibenzotellurophenes exhibited room-temperature phosphorescence in the solid state.The emission wavelength of dibenzotellurophenes can be tuned by substituents,and phosphorescence is not sensitive to air.To confirm their phosphorescent character rather than fluorescence,we used time-resolved spectroscopic experiments,combined with single crystal and powder X-diffraction and density function theoretical calculation?DFT?to verify their phosphorescence properties and elaborate the possible mechanism.These compounds show high potentials as organic light-emitting materials.