Synthesis And Properties Of Novel Phenothiazine Derivatives

Phenothiazine is an aromatic heterocyclic compound with a tricyclic backbone consisting of two benzene rings connected by sulfur and nitrogen atoms.It has attracted widespread attention due to its unique structure and properties.Since 1883,structurally diverse phenothiazine derivatives have been successfully constructed and widely used in pharmaceuticals,optoelectronic materials,and photocatalysis.However,phenothiazine derivatives with extended π-conjugated structures are rarely reported.The π-conjugated extended structure can tune the optoelectronic properties of phenothiazine derivatives,thereby endowing them with excellent photocatalytic properties.This dissertation is devoted to the synthesis of a series of π-conjugated extended phenothiazine derivatives.The π-conjugated extended structures were constructed by incorporating multiple fused benzene rings to the core of phenothiazines to tune the photoelectric properties of phenothiazine derivatives.The research in this dissertation investigates the structure-property relationships of these phenothiazine derivatives and explores their applications in photocatalysis.This dissertation consists of the following three parts:Chapter 1: Firstly,the properties of phenothiazine are introduced.Secondly,the synthesis methods of phenothiazine and its derivatives are summarized.Finally,the application of phenothiazine in optoelectronic materials and photocatalysis is briefly reviewed with examples.Chapter 2: A three-step synthetic transformation strategy was designed to construct five phenothiazine derivatives named 2-2 to 2-6 with up to seven linearly fused rings Their photophysical,electrochemical properties and corresponding free radical cations were systematically studied by UV-vis absorption spectroscopy,emission spectroscopy,cyclic voltammetry,electron paramagnetic resonance and other techniques.The structure and properties of π-conjugated extended phenothiazine were deeply understood from the molecular level.It was found that with the extension of theπ-conjugated structure,the absorption spectrum of phenothiazine shifted to red,and the molar extinction coefficient increased.In addition,2-2 to 2-6 maintain strong excitedstate reduction potentials and can undergo reversible one-electron oxidation processes.Combined with experimental data and theoretical calculation results,it is speculated that they will have great development potential in the field of photocatalysis.Chapter 3: Based on the superior photophysical and electrochemical properties ofπ-conjugated extended phenothiazine derivatives,we used them as photocatalysts in oxidative coupling of amines.The remarkable absorption of 2-4,2-5,2-6 in the visible light region and the strong excited state reduction potential make them have good catalytic performance under visible light.Furthermore,a direct and efficient conversion of amines to imines catalyzed by 2-4 under sunlight in an air atmosphere was successfully realized.The mechanism of the catalytic reaction was systematically studied by DMPO spin-trapping experiment,iodination method,ammonia verification experiment and theoretical calculation.