Studies On Stable Open Shell Singlet Nitroxide/ Hydrazyl Diradical

Singlet diradicals not only provide deep insights into the nature of chemical bonds,but also exhibit interesting physical properties(optical,electronic,magnetic,etc.).So the thesis deals with the studies on stable open shell singlet nitroxide/hydrazyl diradical.It consists of three chapters:In the first chapter,the meaning,types,physical and chemical properties of open shell singlet diradical are briefly reviewed.In the second chapter,several phenylene and pyridylene-bridged binitroxides were prepared and their structures were characterized by X-ray crystallographic analysis.The properties of these binitroxides were investigated by electron paramagnetic resonance(EPR),variable temperature NMR,UV-vis absorption spectra and thermogravimetric analysis(TGA)as well as theory calculations.The results show that these binitroxides possess singlet diradicaloids ground state,which have smaller conjugated systems than the previously reported singlet diradicaloids.The crystals of these compounds can be stored under ambient air and light conditions for months.For the first time,our result demonstrates that singlet diradicaloids can sublime at high temperature with no significant decomposition.In the third chapter,the synthesis and characterization of a new hydrazyl diradicaloid are reported.Structural,spectroscopic,and computational data suggest that the hydrazyl diradical owns the open shell singlet ground state with thermodynamics reversible excited state triplet at high temperature.The singlet diradicaloid has a low oxidation process at Eox1=-0.23 V vs Fc/Fc+,indicating a weak reducibility.The singlet hydrazyl diradicaloid possess remarkable stability in solid state as well as in solution.Moreover,singlet hydrazyl diradicaloid is found to display superior thermal stability,which the thermal decomposition begins at about 175? under inert atmosphere.