Synthesis And Properties Of Triarylamine And Phenothiazine-based Radical Cations

Organic radicals usually refer to the open-shell species containing one or more unpaired electrons in their structures.Due to the presence of unpaired electrons in open-shel-based materials,they usual y exhibit unique physical and chemical properties,such as near-infrared absorption,reversible electron redox,nonlinear optical response,magnetic properties,etc.compared with traditional closed-shell-based materials.In recent years,triarylamine radical cations have shown broad application prospects in the fields of catalysis,semiconductors,and magnetic materials on account of their convenient synthesis and excelent redox properties.The stability of the triarylamine radicals have important influence on the properties of triarylamine-based functional materials.As a consequence,exploring the relationship between the structure of triarylamine and the stability of related radicals is of great significance for the synthesis of new stable triarylamine radicals and their advanced structures,such as macocycle and molecular cage containing triarylamine radicals.In addition,supramolecular radical chemistry is a relatively popular research direction in recent years,and it is a frontier subject of the intersection of traditional supramolecular chemistry and radical chemistry,where the structures,properties and functions of the radicals can be further adjusted by supramolecular method.In this paper,starting from the small triarylamine molecule,the effect of substituents on the redox potential and stability of triarylamine radicals was studied.On the basis of this research,a conjugated phenothiazine macrocycle and two metal coordination cages based on phenothiazine units were used as a platform to finally construct stable macrocycle-and coordination cage-based triarylamine radicals.This thesis mainly includes the following four parts:In chapter one,we briefly introduced the research progress in the design,synthesis and application of organic radicals and triarylamine radicals in recent years.Subsequently,some macrocycles and cages composed of triarylamine radical cation species are comprehensively introduced.In this research background,the research topic of this thesis was proposed.In chapter two,three examples of triarylamine molecules containing different numbers of 3,5-di-tert-butyl-4-methoxyphenyl substituents were designed and synthesized.First of al,it was found by cyclic voltammetry that their oxidation potentials were relatively low,and they could be easily oxidized to triarylamine radical cation species by single-electron oxidants.Systematic comparison of the oxidation potential of the three molecules showed that 3,5-di-tert-butyl-4-methoxyphenyl substituent could effectively reduce the oxidation potential of the triarylamine molecule.Subsequently,the series of triarylamine molecules were oxidized with Ag Sb F₆ to generate the corresponding triarylamine radicals,and the generated radical species were characterized by UV-vis spectroscopy,electron paramagnetic resonance spectroscopy and X-ray single crystal diffraction techniques.Next,the stability of these three radical molecules was studied,and it was found that 3,5-di-tert-butyl-4-methoxyphenyl could greatly improve the stability of the triarylamine radical cations.Finally,it was found that these triarylamine radical species were found to be capable of being oxidized by Cu（II）with higher oxidation potentials to demethylated quinoid cationic salts.In chapter three,the first conjugated phenothiazine macrocycle was constructed by stepwise method using 3,5-di-tert-butyl-4-methoxyphenyl as the side chain of phenothiazine.On the one hand,the radical properties of the conjugated macrocycle were studied by theoretical calculation,cyclic voltammetry,UV-vis-NIR titration as well as electron paramagnetic resonance spectroscopy.It was found that the conjugated macrocycle could be oxidized to the radical specie by a single electron oxidant,and the resulting radical macrocycle had excelent stability.On the other hand,the catalytic properties of the conjugated phenothiazine macrocycle have been studied.The conjugated phenothiazine macrocycle can be used to catalyze the oxidative coupling reaction of primary amines due to its good absorption in visible light region.Compared with small molecules and trimers,the conjugated macrocycles have better catalytic effect.In chapter four,firstly,phenothiazine pyridine ligands and alkynyl pyridine ligands with 3,5-di-tert-butyl-4-methoxyphenyl as the side chain were designed and synthesized.Then,two examples of phenothiazine metal coordination cages were successfully obtained by self-assembly of pyridine ligands with Pd（II）.Based on the two metal coordination cages,two challenging radical metal coordination cages were synthesized by simple oxidation reaction.The properties and stability of radical cages were systematically studied by electron paramagnetic resonance spectroscopy and UV-vis spectroscopy.It was found that two cases of metal coordination cages could be completely oxidized to obtain multi-radical metal coordination cages,and the resulting radical metal coordination cages had excelent stability.What is more,due to the excelent stability of the radical cage,the first single crystal of radical metal coordination cage was successfully obtained.