Study On Synthesis And Properties Of Stable Carbon Radicals Of Polycyclic Aromatic Hydrocarbons

As a highly active open-shell molecule,carbon radicals of polycyclic aromatic hydrocarbons have great application potential in the fields of electricity and magnetism because of their unbonded electrons,unique electronic structure and unique physicochemical properties.The carbon center free gene has the trivalent characteristics of the central carbon atom,which can realize structural diversification and complex molecular design,but its stability is poor,and it is easy to find dimerization reaction or oxidation by oxygen in the air to form closed-shell compounds.Based on this,researchers proposed two synthesis strategies of electron spin delocalization and steric hindrance protection to improve the thermodynamic stability and kinetic stability of carbon radicals,so as to prepare carbon radical molecules with good stability.Representative molecules of carbon radicals of polycyclic aromatic hydrocarbons are Open-shell Graphene Fragments（OGFs）.Open-shell graphene fragments（OGFs）include single,double,and multiradical molecules based on molecular graphene fragments.In the early stage of research,the research of OGFs was mainly limited to finacene systems with highly symmetric structures,and with the advancement of synthesis strategies and characterization methods,their systems became more and more complete and rich.For relatively few carbon monoradicals with asymmetric structure,Benzoanthracenyl（BAR）is the simplest asymmetric open-shell graphene fragment,and its research stays at the level of electron spin resonance spectroscopy（ESR）and theoretical research,stable benzanthracene radicals and their derivatives have not been reported,and their physical and chemical properties are also unknown.For diradical polycyclic aromatic hydrocarbons,they show great application potential in organic electronics and spintronics because of their unique properties such as low energy band gap and strong intermolecular spin-spin interaction.Therefore,this paper mainly focuses on carbon monoradicals with asymmetric structure and biradical polycyclic aromatic hydrocarbons withπconjugation.The first work in this paper revolved around benzoanthene radicals.We synthesized the first stable benzoanthracene radical derivative BAR1 by introducing large steric hindrance substituents at multiple sites of BAR radicals.Due to steric hindrance protection at multiple sites,BAR1 radicals have good stability with a half-life of 108 hours.Through EPR spectroscopic testing,about 26 high-resolution lines were obtained,which is more reliable and easy to analyze than the parent BAR with 350 high-resolution lines.In addition,it has the characteristic absorption of single radicals in the near-infrared region（600 nm～800 nm）,and shows two reversible single-electron oxidation and reduction waves on the cyclic voltammetric curve.Through the above analysis of magnetic,optical and electrical properties,the physicochemical properties of free radical BAR1 and its asymmetric structure were highly correlated.We also synthesized its corresponding cation BAR1⁺,whose structure is clearly determined by two-dimensional NMR spectroscopy,which in turn verifies the structure of neutral radicals BAR1.However,due to its asymmetry and steric hindrance effect of multi-site substituents,we were unable to prepare a single crystal of BAR1.The second work of this paper revolves aroundπconjugated-extended biradical polycyclic aromatic hydrocarbons.Based on the previous work of our group,we found that biradical polycyclic aromatic hydrocarbons with good stability can be used to prepare field-effect transistors（OFET）based on their biradicals and exhibit high mobility(0.15 cm² V^-1 s-¹)and good bias stability and storage stability.Therefore,we try to prepare Z-type dibenzooctaphenyl biradicals 8 with better stability byπconjugate extension,increase the conjugation to improve the thermodynamic stability,and introduce triisopropylsilynyl with large steric hindrance（TIPSe）at the site with high electron spin density to improve the kinetic stability,and further study its application on OFET devices.However,due to the poor solubility of its reaction precursor 7 and the possible presence of isomers 71 and 72,the synthesis of 8 was unsuccessful.Based on this,we designed a new optimized synthesis route,that is,the introduction of methyl groups at position 2 of the reaction precursor 1-pyreneboronic acid,which can effectively avoid the formation of isomers 71 and 72.However,due to time reasons,its optimization plan could not be fully completed,and we will improve it in the future.